Room-temperature plasticity in Ag_2Te induced by Ag ions hopping

Domain: neuroscience
Published: 2026-02-05
Editorial outcome: minor_revision

Abstract
The discovery of silver chalcogenides ductile semiconductors with high room-temperature plasticity holds significant promise for the development of bendable thermoelectric and electronic devices. However, the atomic-scale origins of their plasticity, ranging from dislocation slip to sublattice amorphization, remain diverse and material-specific. Here, we report a distinct deformation mechanism in Ag2Te through stress-driven and ionic-hop-mediated domain rotation. By in-situ scanning/transmission electron microscopy (S/TEM), we directly observe the hopping of Ag ions to adjacent vacancies stabilizes the deformed Te-sublattice and facilitates a coordinated ~92.2° lattice rotation that accommodates substantial plastic strain. This mechanism, which preserves long-range crystallinity, contrasts with both traditional dislocation-mediated plasticity and stress-induced amorphization pathways. Combined with its excellent thermoelectric performance (ZT value of ~0.67) at room temperature, Ag2Te emerges as a promising flexible electronic material.

Introduction
Flexiblesemiconductorshavereceivedalotofattentionduetotheir potentialinthedevelopmentofbendable,stretchableandwearable electronic devices, such as thermoelectric generators and flexible transistors1–9. Notably, several inorganic semiconductors, primarily chalcogenides, have been discovered to exhibit significant room- temperature plasticity1,10–24. This unique property enables the direct integration of robust electronic components into flexible systems, bypassingtheneedforcomplexfilm-on-substratearchitectures25–31. Despite these promising prospects, the atomic mechanisms responsible for large plastic deformation in these inherently brittle materialsarediverseandnotfullyunified.Earlystudiesoftenattributed plasticityto dislocation motion and stacking faults17,32–45. More recentworkonsilverchalcogenideshasrevealedalternativepathways; forinstance,plasticityinAg2Shasbeenlinkedtometallic-likebonding andwavyslipplanes12,whileresearchonAg2Te1-xSxsolidsolutionshas uncoveredamechanisminvolvingstress-inducedsublatticeamorphi- zationstabilizedbymobileAgions19,46.InAg2Tenanowires,plasticityis attributedtothesynergisticeffectsofdislocationemission,slipband formation,deformationtwinning,andAgnanobridges47.Thisdisparity indicates that a one-size-fits-all model is insufficient, and material- specificmechanismsawaitdiscovery.

Ag2Teisasemiconductorwithbothionicandcovalentbonding characteristics48–54 that exhibits remarkable room-temperature plasticity17,55 and is concurrently recognized as a promising near- room-temperature thermoelectric material17,50,55–58. The plasticity enhancement strategies for Ag2Te have continuously developed to tackle the inherent brittleness bottleneck of inorganic semi- conductors,progressingfromnano-structuring(e.g.,nanowires)47to micro-engineering (e.g., domain boundaries)55 and down to atomic- scale mechanisms (e.g., sublattice amorphization)46. These mechan- ismsnotonlysignificantlyimproveductility(achievingstrainsupto 75.7%innanowiresandtensileductilityof10,150%inbulkmaterials) butalsooptimizethermoelectricperformancethroughphononscat- tering(withZTvaluesenhancedto0.6–2.2).Intriguingly,whilehigh-S materialsaregenerallyductile59,Ag2Testandsoutasoneoftheductile high-Te materials, suggesting a potentially unique deformation mechanism.Here,wecombinemacroscopictestswithin-situelectron microscopytorevealtheoriginofplasticityinAg2Te.Wediscovera previously unrecognized mechanism—ionic-hop-mediated domain rotation—thatisdistinctfrombothconventionaldislocationslipand the recently reported sublattice amorphization. In this process, the crystalline Te-sublattice undergoes a coordinated large rotation, enabledbythediscretestress-inducedhoppingofAgions.Thiswork not only resolves the deformation mechanism in Ag2Te but also establishes a strategy for achieving plasticity in functional semi- conductorsbyharnessing ion migration to drive crystalline reconfi- guration, thereby bridging the understanding of its exceptional mechanicalandelectronicproperties.

Results
Room-temperatureplasticityinAg2Te
Althoughtherearemanystructuralvariants,theα-Ag2Tesampleused in our experiments is determined to have the monoclinic structure (a=8.1616Å,b=4.4665Å,c=8.9733Å,β=124.153°)asindexedbythe powderX-raydiffraction(XRD)pattern(SupplementaryFig.1).Using theMTSuniversaltestmachine(SupplementaryFig.2a),thetensile ductilityofbulkAg2Teatroomtemperaturehasbeenobserved.The sizeofbeamsbeingtestedis8×4×3mm3(Fig.1a).Figure1bshowsthe typical room-temperature stress/strain curve of Ag2Te, under the applied tensile stress. Although variations (surface roughness and other factors) during the preparation of Ag2Te beams caused dis- crepancies in the measured results (Supplementary Fig. 2b), the majorityofmeasuredresultsareclosetothosepresentedinFig.1b.All the samples show a large tensile deformationatroom temperature withtheaveragetensilestrainof~12.13%.Furthermore,opticalphotos of the Ag2Te beam before and after tensile testing (Supplementary Fig. 2c) show a nearly uniform elongation due to the ductile deformation.

WetheninvestigatedthetensilepropertiesofAg2Teatamicro- scopiclevelbyin-situtensileforceS/TEMexperiment(Fig.1c,dand SupplementaryVideos1–3).Theschematicofthenanochipusedinthe tensileforceexperimentsisshowninSupplementaryFig.3.TheAg2Te samplewascutintoabeamof800×300×~100nm3byfocusedion beam(FIB)andthentheforcewasappliedalongthelongestedge.As showninFig.1c,beforetheforcewasapplied,thethinbeamisasingle crystalorientedalongthe[021]zoneaxis,identifiedbythehigh-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)imageandthecorrespondingfastFouriertransform (FFT)image.Whenthetensileforcewasapplied,thebeamwasgra- dually elongated (Supplementary Videos 1–3). Figure 1d shows the HAADF-STEM images of Ag2Te when the deformation reaches 0%, 3.69%, 10.33%to12.29%,respectively.Themaximumtensilestrainof thebeamreaches12.9%beforefracture,asshowninFig.1e,similarwith thatobservedinbulkAg2Te.AsshowninSupplementaryFig.4a,after fractureofthebeam,thereisnoclearsignofnecking,andthefrac- turedAg2Tehasthesamecrystallinestructure,asidentifiedbySTEM imaging.Also,thestoichiometricratioofAgtoTeremainsasthe2:1,as identifiedbytheenergydispersivespectrometer(EDS)mappingand the corresponding line-scan quantification (Supplementary Fig. 4b). TheseobservationsimplythattheAg2Tehasplasticityatroomtem- perature, while its deformation mechanism may be different from thoseofplasticmetals.

Themicrostructuralmechanismofroom-temperatureplasticity
We find that the large tensile deformation of Ag2Te is primarily mediated by the formation of coherent rotation domains—crystal- lographic regions that undergo a specific ~92° lattice reorientation relative to the original matrix. Crucially, our analysis reveals that conventional defects like dislocations, twins, or stacking faults are conspicuously absent as dominant features in the deformed microstructure.

The microstructure evolution in Ag2Te during stretching was investigated.AsshowninFig.2a,numerousrotationdomainsformed within the original [021]-oriented Ag2Te crystal after deformation. HAADF-STEMimaging(Fig.2b)clearlyidentifiesboththeoriginal[021] domain([021]OD)andanewlyformed[021]rotationdomain([021]RD). Thetwodomainsmaintainacoherentboundaryandarerelatedbya consistentrotationangleof~92.2°.

TheFFTpatternsfromthe[021]ODand[021]RD(Supplementary Fig. 5a) provide definitive crystallographic evidence that this is a rotation domain, notatwin.TheyellowdashedlineintheFFTrepre- sentsthetraceofthe(012)plane,whichwouldbethemirrorplaneif thiswereadeformationtwin.Thistraceisdeterminedgeometricallyas the line through the FFT center that is perpendicular to the vector connectingthecentertothe(012)diffractionspot.Asdemonstrated, thediffractionspotsfromthe[021]RD(redcircles)donothaveamirror symmetrytothesespotsfromthe[021]OD(bluecircles)acrossthisline. Instead,theentirediffractionpatternfromthe[021]RDisrotatedby ~92.2°withrespecttothatofthe[021]OD(SupplementaryFig.5b).The absenceofsuchmirrorsymmetryconfirmsthenon-twinnednatureof thedomainboundary.

Suchasimilardomaintransitionwasalsoobservedinthetensile experimentofbulkAg2Te as evidenced bythe electron backscatter diffraction (EBSD) mapping as showninFig. 2c and Supplementary Fig.6.TheEBSDmap(Fig.2c)clearlyshowstheformationofmany rotation domains near the fracture of the bulk sample. The angle betweenthetworotationdomainsiscloseto~91.8°(asmarkedbythe bluelinesinFig.2c),similartotheorientationdomainsobservedbyin- situ S/TEM (Fig. 2b).Incomparison, farfewer rotation domains are observedintheareafarfromthefracture(SupplementaryFig.6b).It canbededucedthattherotationdomainsareformedundertensile stress,especiallytheareasthatunderwentalargedeformation.

Furthermore,thefracturemorphologyofbulkAg2Teasshownin SupplementaryFig.6arevealsnoevidenceofnecking,consistentwith the observations in both Supplementary Fig. 2c and Supplementary Fig. 4a. This behavior starkly contrasts with the deformation char- acteristicsofmostplasticmetals.ThedeformationinAg2Testemsfrom thestress-inducedrotationaldomaintransformation.Unlikeconven- tionalplasticdeformation,whichreliesonlocalizedsheardeformation through dislocation slip, domain transformation represents a con- tinuous nucleation and growth process throughout the material matrix. When external forces are applied, numerous rotational domains sequentially nucleate within stress-concentrated regions, collectively coordinating macroscopic strain. This distributed, non- localizedstraincoordinationeffectivelypreventstheconcentrationof plasticinstabilitywithinnarrowregions,therebysuppressingnecking formation.Consequently,theobservationof“neck-free”deformation supports our proposed mechanism where domain transformation dominatesandcoordinatesplasticdeformation.

Whilethemajorcontributiontothedeformationisfromforma- tionoftherotationdomains,theotherformofdomaintransition,i.e., theformationofasmallnumberofdomainsalongotherorientations, isalsoobserved.AsshowninFig.2d,smalldomainsalongthe[214]and [736]axisareobserved.Duetothecomplexinteractionoftheapplied stress and the polycrystalline sample, it is not surprising thatsmall domains along other zone axis are occasionally found during the stretchingdeformation.

Atomicmechanismofroom-temperatureplasticity
Ouratomic-scaleobservationsrevealthattheplasticityofAg2Teori- ginatesfromastress-drivenionic-hop-mediateddomainrotation.This process is initiated by an anisotropic deformation of the rigid Te- sublattice, which triggers the coordinated hopping of Ag ions, ulti- matelyleadingtoamacroscopiccrystalreorientation.

As shown in the HAADF-STEM image (Fig. 3a) and the corre- sponding schematic (Fig. 3b), the transformation under tensile stress involves a substantial deformation of the Te-sublattice. The spacing between the atomic columns identified as Te-dominated (specifically, Te-Ag mixed columns) by image simulation (Supplementary Fig. 7) substantiallyincreasesfrom0.34nmto0.40nmalongthetensileaxis, whilebeingcompressedtransversely.Thisdistortiondirectlysqueezes the Ag ions out of their original tetrahedral sites. In the structure of Ag2Te(SupplementaryFig.8a),bothAg1andAg2sitesresidewithinTe tetrahedra, with intrinsic vacancies concentrated in the (100) plane (SupplementaryFig.8b).ThestressforcestheAgionstohopintothese adjacent vacant sites within the expanded tetrahedra. This discrete, stress-induced ionic hop is the critical step that unlocks the lattice, allowing the entire vacancy-concentrated (100) plane to undergo a coordinated~92.2°rotation,therebyformingthenewdomain.

Theresultingstraindistribution,mappedbygeometricphaseana- lysis(GPA)inFig.3candquantifiedinFig.3d,providesdirectevidenceof howstrainisaccommodatedunderthemechanism.The~92.2°rotation effectivelyreleasestheelasticstrain,asseenintherelaxationoftheεxx componentfrom~−9.3%inthe[021]ODto~−2.8%inthe[021]RD.Based onthehoppingmodel,thepredictedtensiledeformationalongthemain stress direction is ~17.6%, which aligns with the maximum strain observedinthebulktensiletests(SupplementaryFig.2).

First-principlesDFTcalculationswereperformedtoquantitatively validate this atomic-scale hopping mechanism. We calculated the migrationbarriersforthetwomostprobablepaths(Path1andPath2, Fig.4a)connectingadjacenttetrahedralsitesinvolvedinthedomain rotation.Thecalculationsshowthatthemigrationbarriersforboth paths are comparable, at about 0.47eV and 0.44eV without strain (Fig.4b),indicatinglowanisotropyforionhopping,whichfacilitates cooperativemigration.Crucially,undera2%latticestrain(withinthe (100) plane), the barrier for path 1 is reduced to 0.43eV (inset of Fig. 4b), demonstrating that the deformation of the Te-sublattice actively promotes Ag ions migration. Furthermore, the calculated diffusioncoefficientofAg+is~25timeslargerthanthatofTe2−(Sup- plementary Fig. 9b), confirming the preferential mobility of the cations. Together, these calculations confirm that the deformation- inducedhoppingofAgionsisafeasibleandfavorableprocess.The critical role of Ag+ migration suggests that the stoichiometry, and hencetheAgvacancyconcentration,inAg2+xTeisexpectedtobeakey factorinmodulatingitsplasticbehavior,offeringapromisingavenue forfuturematerialsengineering.

Bothastrain-softeningandstrain-hardeningeffectsareobservedin themacroscopictensileresponsesinbulkAg2Te,asshowninFig.1band SupplementaryFig.2b,respectively.Whenthetestedsampleshavea differentmicrostructure,thedomainrotationmechanismcouldman- ifestindifferentmodes.Whenthereformssmallnumberofnewdomain boundariesinbiggrains,onemayobservethestrain-softeningeffect(as showninFig.1b).Wheninvolvingthesequentialnucleationofmultiple domain boundaries, their cumulative interactions can lead to strain- hardeningbyresistingfurtherdeformation(asshowninSupplementary Fig.2b).Bothin-situandex-situmicrostructuralstudyonthedeformed Ag2Tesamplesrevealthedeformationismainlyaccommodatedbythe formation of rotation domains and domains boundaries. We seldom observeotherdefects(suchastwins,stackingfaultsanddislocations)in thedeformedareas.However,asdislocationsrefertothelatticemis- match,intheboundaryof[021]RDand[736]domains(despiteformation ofthe[736]domainisrare,Fig.2d),therewouldbecomplicateddis- locationstoaccommodatethelatticemismatch.

Inconclusion,wehaveunveiledapreviouslyunrecognizedplas- ticitymechanisminAg2Te:stress-drivenionic-hop-mediateddomain rotation.Itisthesynergisticinterplaybetweenthedeformationofthe Te-sublatticeandthesubsequenthoppingofAgionsthatenablesthe large,coherentlatticerotation,distinguishingitfundamentallyfrom conventionaldislocation-basedplasticityordeformationtwinning.

Compatibilityofplasticityandthermoelectricproperties
Thepracticalpotentialofafunctionalsemiconductorisdeterminedby the synergy between its mechanical and electronic properties. In Ag2Te, the room-temperature plasticity governed by ionic-hop- mediated domain rotation is complemented by its decent thermo- electric performance. The conductivity (σ), Seebeck coefficient (α), powerfactor(PF),andthermalconductivity(κ)areshowninSupple- mentary Fig. 10d. The electrical conductivity shows a metallic-like temperature dependence, while the Seebeck coefficient indicates n-typeconduction. As showninFig.4c,apeakZTvalueof~0.67 is achievedat400K.Adirectcomparisonatauniformtemperatureof ~400K9,23,30,37,60–68(Fig.4d)confirmsthatthisZTvalueiscomparableto otherstate-of-the-artroom-temperatureductilesemiconductors.This demonstratesthatAg2Tesuccessfullycombinesauniquedeformation mechanism with high thermoelectric performance, suggesting its potentialforflexiblethermoelectricapplications.

Thecompatibilityofthisuniqueplasticitymechanismwithfunc- tionalpropertiesisakeyadvantage.Priorstudiesoncloselyrelated Ag2Te1-xSexcompoundshavedemonstratedthatextraordinaryroom- temperature plastic deformability can coexist with a high thermo- electric Figure of merit (ZT>0.6)17. This is because chemical stoi- chiometryandoverallchemicalbondingpreserveduringdeformation, avoidingintroductionofthedetrimentaldefectsthatwouldseverely degradeelectronictransport.

Ourdiscoveredmechanismofionic-hop-mediateddomainrota- tion further distinguishes itself from other plasticity pathways in Ag2Te.Forinstance,inAg2Tenanowires,exceptionalductilityhasbeen attributedtodeformationtwinningonthe(001)plane,followedbyAg precipitationunderextremestress47.Incontrast,theplasticityinour bulkAg2Tesamplesisachievedwithoutphaseseparationortwinning, butthroughacoherentlatticerotation.Thisdistinctionunderscores thematerial-specificnatureofplasticdeformationandhighlightsthe uniqueadvantageofthemechanisminpreservingbothcrystallinity and chemical stoichiometry, a prerequisite for maintaining optimal thermoelectricfunction.

Methods
Materialssynthesis
Ag2Te was prepared by vacuum melting and annealing. A stoichio- metric amount of Ag (99.99%, Sinopharm, China) strips and Te (99.99%) were weighed and mixed. The mixtures were sealed in evacuated quartz tubes and heated in a furnace, up to 1273K at 1.5Kmin−1 and kept for 10h. To obtain homogeneous ingots, the quartztubeswererockedevery2hat1273K.Subsequently,thetubes wereslowlycooleddownto673Kattherateof1Kmin−1.Theresulting ingotswerefurtherannealedat673Kfor3daysandthencooleddown to 373K, and held for 2 days. The obtained ingots were cut into a propershapeforcharacterizationandperformancemeasurement.The constituent phases were identified by XRD (Empyrean, Cu Kα line, PANalytical,Holland)andtheresultshowsthattheAg2Teinourwork hasamonoclinicstructure,witha=8.1616Å,b=4.4665Å,c=8.9733Å, β=124.153°;spacegroupP21/c(SupplementaryFig.1).Here,wereferto themonoclinicphaseasα-Ag2Te.

Instrumentation
The tensile tests were performed using an MTS universal testing machine (MTS E44.104, Supplementary Fig. 2a). Key parameters, includingthestrainrate,elasticmodulus,andtotalstrainatfracture, were determined from the tensile stress-strain curves. These para- metersreflectthematerial’splasticityandresistancetoelasticdefor- mation. The tensile yield strength, defined as the maximum stress during the failure process, was calculated using the formula: σy=F=(b×W),whereFrepresentedthemaximumappliedload,bwas thesamplebeamthickness,andWwasthesamplebeamwidth.

Thin TEM samples were prepared by Focused Ion Beam (FIB) milling (Helios Nanolab G3 UC, FEI). TEM characterization of the samples was carried out using a double Cs-corrected Scanning TransmissionElectronMicroscope(STEM,TitanThemisG260-300, FEI).Forthein-situmechanicalexperiments,ananochipwithforceand thermalholder(Mini-lab,Bestron)wasused,asshowninSupplemen- taryFig.3b.TheTEMsamplewasmachinedintotheshapeofabeam andtheforceisappliedalongthelongestsideofthebeam.

DFTcalculation
AllstructuraloptimizationswereperformedusingtheViennaAbinitio Simulation Package (VASP) software69–71. The Projector Augmented Wave(PAW)method70,72andthePerdew-Burke-Ernzerhof(PBE)71gen- eralized gradient approximation (GGA) exchange-correlation func- tional were employed for relaxation calculations. The plane-wave kineticenergycutoffwassetto500eV.Ak-pointmeshof3×6×3was used to ensure convergence. By balancing computational cost and accuracy,thetotalenergyconvergencecriterionforstructuralopti- mizationwassetto10−8eV,andallstructureswerefullyrelaxeduntil the forces acting on all atoms converged to below 0.01eV/Å. Sub- sequent transition state calculations utilized the climbing image nudged elastic band (CI-NEB) method73, inserting seven images between the initial and final states. Ab initio molecular dynamics (AIMD) simulations were conducted using a 2×2×4 supercell con- taining192atoms.Thesystemwassimulatedinthecanonical(NVT) ensembleat600Kand773K,employingatimestepof2fsforatotal simulationtimeof8ps.

The specific Ag migration paths investigated by the CI-NEB method (Fig. 4a) were selected to directly test the atomic-scale mechanism obtained from the experimental observations (Fig. 3b). Theinitialandfinalstatesweredefinedastheconfigurationswiththe Agionsresidingintwoadjacent,symmetry-equivalenttetrahedralsites thatshareacommonvacancy.Thecalculatedpaths(Path1andPath2) correspond to the most geometrically straightforward hopping tra- jectoriesbetweenthesesites,whichareintegraltothedomainrotation process.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study employs in-situ tensile scanning transmission electron microscopy (S/TEM) to reveal the stress-driven domain transformation and plastic deformation behavior of Ag2Te at room temperature. This work provides significant insights into the anomalous plasticity mechanisms of covalent/ionic-bond semiconductors, particularly by proposing a novel “cation hopping-lattice cooperative deformation” mechanism that transcends traditional dislocation-based plasticity theories. This may open broad prospects for developing high-strain-rate flexible semiconductor devices at room temperature. I would recommend minor revision before it can be further considered. Here are the comments in details:\n1. The manuscript mentions that \"As shown in Figure S4a, after fracture of the beam, there is no clear sign of necking, and the fractured Ag2Te has the same crystalline structure... \" Here, the author explicitly states that the FIB-prepared nanoscale specimens exhibited no discernible necking phenomenon upon fracture. In contrast, when describing tensile tests on bulk specimens, the author only presents the stress-strain curve without mentioning the post-fracture morphology. It remains unknown whether necking occurs during fracture of macroscopic samples. If necking does occur at the bulk scale, could it be inferred that sample size or surface effects are the primary drivers of plastic deformation?\n2. Figure 3c presents a strain field map obtained through geometric phase analysis (GPA). The accuracy of GPA is highly dependent on the selection of the reference area and the correct identification of the unstrained region. I recommend that the authors explicitly label the reference area used for GPA calculations in the Figure 3c illustration. Additionally, line scan profiles of the strains (εₓₓ,，εᵧᵧ) should be provided to quantitatively demonstrate the magnitude of strain variation and distribution width across domain boundaries, rather than relying solely on qualitative color contrasts.\n3. The manuscript mentions that \"a 2% strain\" was applied in the DFT calculations to demonstrate the reduction of Ag⁺ ion migration barriers. However, the type of applied strain (e.g., uniaxial, biaxial, or volumetric) and its crystallographic direction are not specified. To strengthen the correlation between the computational models and the experimental tensile stress conditions, it is crucial to clarify these parameters.\n4. I would appreciate additional details on the relationship between thermoelectric properties and plasticity mechanisms. How does plastic deformation influence its thermoelectric properties?\n5. Fig. 1b: Please state the strain rate and direction of stretching used for the bulk tensile test. And Fig. 3a: The purple rectangles highlighting the lattice distortion should be more clearly labeled and described in the caption.\n6. The manuscript measured the deformation of the Te sublattice (0.34 nm → 0.40 nm) via HAADF-STEM images (Figure 3a). The contrast in HAADF images depends on the total scattering power of atomic columns (related to the square of atomic number and atomic count). In the [021] orientation of Ag2Te, the atomic structure comprises mixed atomic columns composed of both Ag and Te atoms, as well as pure Ag atomic columns. Bright spots in the image correspond to mixed columns rich in Ag atoms (scattering superposition from multiple Ag atoms), not pure Te atomic columns. If spacing measurements were inadvertently taken between two mixed columns or between a mixed column and a Te column, the measured deformation would not reflect pure Te sublattice deformation, and the measurement accuracy would be questionable.\n7. The manuscript has described a mechanism involving “Ag⁺ ion hopping stabilizing the deformed Te sublattice.” But can this be refined into a more universal theoretical model or physical picture? For example, can this material be regarded as a “semi-solid” or “pseudo rheological” system, where the rigid Te sublattice framework undergoes plastic relaxation by the flow of ions.", "reviewer_2": "This work studied the mechanism of room-temperature plasticity in Ag2Te. By in-situ scanning and transmission electron microscopy investigations, the authors demonstrated that the Ag+ ion hopping and Te-sublattice deformation are the source of plasticity. I find this conclusion arbitrary and lack of sufficient comparisons with other mechanisms reported in this material system. Moreover, the manuscript is not well-organized, and the writing could be significantly improved. Therefore, I cannot recommend this manuscript for publication in Nature Communications. The following comments should be addressed before they submit the paper to another journal.\n1. At the very beginning of the Abstract, the authors highlighted the importance of silver sulfide and emphasized that the origin of plasticity in such materials remains poorly understood. However, this work focuses on Ag2Te, not Ag2S. Moreover, the mechanisms of plasticity in Ag2S or Ag2S-Ag2Te alloys have been well investigated by many studies, such as [Shi et al., Nat. Mater. 2018, 17, 421-426; Yang et al., Adv. Mater. 2021, 2007681; Wang et al., Adv. Funct. Mater. 2023, 2300189; Wang et al., Nat. Mater. 2025, doi.org/10.1038/s41563-024-02112-7; Hu et al., The Innovation, 2022, 3, 100341]. The authors should clarify the differences between the Ag hopping mechanism and those reported in the literature, and explain why the new mechanism takes over.\n2. In the main text, the authors should (but they did not) provide an overview of previous research progress on the plasticity of Ag2Te, nor did they include any description related to thermoelectric properties.\n3. The introduction regarding previous studies on plastic semiconductors is overly general. At present, numerous plastic semiconductors have been reported, and a variety of plasticity mechanisms are proposed. Yet, the authors simply attribute them to dislocation motion and stacking fault mechanisms.\n4. Are the rotation domains twins of the original domains? It has been demonstrated in this work [Wu et al., Adv. Funct. Mater. 2025, 35, 2423014] that many deformation twins form along the (001) plane, which inhibits crack initiation. I do not see clear evidence of Ag hopping. It could be a simple structural deformation and twinning-induced plasticity.\n5. The DFT calculated migration barrier for Ag+ shows minimal variation. More details about the selection of the NEB path should be provided and compared.\n6. The ZT values reported in this manuscript are not high among plastic semiconductors. Furthermore, the comparison of ZT in Figure 4d is selective, which does not represent the state-of-the-art of ductile thermoelectrics. The authors should either stick to the maximum ZT value reported in each work or make the comparison at the same temperature. Alternatively, they can also compare the temperature-dependent ZT curves. In addition, corresponding references to the data in Figure 4d must be indicated clearly.", "reviewer_3": "In this manuscript, the authors demonstrate that the hopping of Ag ions could enable plasticity in Ag2Te, and the obtained Ag2Te has good TE performance. However, the deformation mechanism, including the Ag ions hopping and rotation domains, is not well clarified. In addition, the tensile results in this work are not consistent, and there are obvious errors in basic concepts and knowledge, raising concerns about the reliability of this work. Moreover, the reported TE performance is not outstanding among previous articles. I would not recommend this work for publication at this stage, considering these scientific issues.\n1. The current evidence for “Ag ions hopping” remains insufficient. Ionic conductivity measurements would offer additional experimental support. In addition, as the exact migration path of Ag ions is unknown, how to define path 1 & 2? On the other hand, references 47-50 do not state that monoclinic Ag2Te contains ionic bonding. Please provide more evidence from experiments or theoretical calculations.\n2. The manuscript attributes plasticity of Ag2Te to the formation of rotation domains. But what are these domains? And how are they formed? These crucial issues are not clarified. In addition, other defects, including dislocations, twins, and staking defects, are not studied or discussed.\n3. The high diffusion coefficient of Te atoms (Fig. S7) is doubtful, in contrast to its rigid sublattice characteristic. Taking Ag2S as an example, the diffusion coefficients of S atoms in both monoclinic structures and superionic conductors are near 0.\n4. The tensile results for bulk Ag₂Te in Fig. 1b and Fig. S2b are contradictory: Fig. 1b exhibits a strain-hardening effect, whereas Fig. S2b shows no strain hardening—instead, the stress even decreases after yielding. Such inconsistent mechanical responses in the same material should not be caused by sample preparations.\n5. In the background, the statement “high-Te materials are typically brittle55” is incorrect. Both Ag2Te0.7S0.3 and Ag2Te0.6S0.4 are Te-rich but show especially high ductility. In addition, reference 55 talks about Ag2(Se,S), not Ag2(Te,S).\n6. The author misuses “strain rate” to describe the deformation degree, e.g., “the average tensile strain rate of ~10.6%”. “Strain rate” defines the time derivative of strain (s⁻¹) (PRL 100, 025502, 2008).\n7. The phrase “Ag+ ions” is wrong. “Ag+” already implies ionic nature and charge of silver, and combining “Ag+” with “ions” creates unnecessary repetition. Use either “Ag+” or “Ag ions”.\n8. There has recently been a work that reveals Ag-ion diffusion is crucial for the plasticity of Ag2Te1–xSx semiconductors (Nat. Mater. 2025). Is there anything different or common compared with this work? In addition, the plasticity of Ag2Te has been reported before (Adv. Mater. 2023, 35, 2302969), and the thermoelectric performance of Ag2Te in this work is not outstanding compared with the previous work either.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_5": "In this work, Guo et al. demonstrate that the hopping of Ag⁺ ions to adjacent vacancies stabilizes the deformed Te-sublattice under the applied stress and thus enabling a large plasticity in Ag2Te. Furthermore, this hopping mechanism is directly observed by in-situ scanning and transmission electron microscopy (S/TEM). This is a comprehensive and well-structured study that provides valuable mechanistic insight into large plasticity in covalent/ionic bonded and ion-conductive semiconductors. I would like to recommend it for publication after some changes:\n1. The large plasticity is attributed to the hopping of Ag⁺ ions to adjacent vacancies. Does the slight Ag variation of Ag2+xTe have influence on the mechanical properties?\n2. What is the direction of the two migration paths of Ag⁺ ions in DFT calculations? And why are these two paths chosen for calculations? Are there specific crystallographic planes or directions that facilitate this hopping more readily than others?\n3. How does the plasticity mechanism respond to different strain rates? Is there a critical strain rate beyond which the Ag⁺ hopping mechanism becomes too slow to accommodate the deformation, leading to brittle fracture? Conversely, at very low strain rates, does the material exhibit even greater plasticity?\n4. There are a few typos in the manuscript such as “Temsile” in Fig 1b, “Figure 6a” in line 137."}, "author_response": "Responses to Reviewers’ comments\nReview: Room-temperature plasticity in Ag Te induced by Ag ions hopping.\n2\n(NCOMMS-25-66818-T)\nBy Anan Guo, Keke Liu, et al.\nDear Reviewers:\nWe express our sincere gratitude to the reviewers for dedicating their time and effort to\ncarefully review our manuscript and provide insightful comments. We truly appreciate\ntheir valuable suggestions. We have revised our manuscript in response to their\nfeedback, and the point-by-point responses to their comments are enclosed.\nReviewer #1 (Remarks to the Author):\n1. The manuscript mentions that \"As shown in Figure S4a, after fracture of the beam,\nthere is no clear sign of necking, and the fractured Ag Te has the same crystalline\n2\nstructure... \" Here, the author explicitly states that the FIB-prepared nanoscale\nspecimens exhibited no discernible necking phenomenon upon fracture. In contrast,\nwhen describing tensile tests on bulk specimens, the author only presents the stress-\nstrain curve without mentioning the post-fracture morphology. It remains unknown\nwhether necking occurs during fracture of macroscopic samples. If necking does occur\nat the bulk scale, could it be inferred that sample size or surface effects are the primary\ndrivers of plastic deformation?\nAuthor Reply: Thank you for your insightful and constructive feedback. You have\ncorrectly highlighted the importance of clarifying the “neck-free” phenomenon and its\nintrinsic connection to the deformation mechanism we proposed. We fully concur with\nyour perspective and have carried out additional experiments and revised the\nmanuscript in accordance with your suggestions:\n1. In the Supplementary Fig. S6a added in the revised SI, we present the typical\nfracture morphology of a macroscopic tensile specimen after failure. As\nexpected, no significant local necking was observed in the macroscopic\nspecimen either. Its fracture morphology exhibits a relatively flat fracture\nsurface, consistent with observations from nanoscale specimens. This\nprovides a strong evidence that “neck-free fracture” is an intrinsic\ndeformation characteristic by Ag Te across scales from the nanoscale to the\n2\nmacroscale.\n2. Based on this, we have added the following paragraph to the main text of the\nrevised manuscript (line 150-163), aiming to directly link the “no-neck-\nshrinkage” phenomenon to our proposed “domain rotation mechanism”:\n“Furthermore, the fracture morphology of bulk Ag Te as shown in\nmicrostructural observations (Supplementary Fig. 4a). This behavior starkly\ncontrasts with the deformation characteristics of most plastic metals. The\ndeformation in Ag Te stems from the stress-induced rotational domain\n2\ntransformation. Unlike conventional plastic deformation, which relies on\nlocalized shear deformation through dislocation slip, domain transformation\nrepresents a continuous nucleation and growth process throughout the\nmaterial matrix. When external forces are applied, numerous rotational\ndomains sequentially nucleate within stress-concentrated regions, collectively\ncoordinating macroscopic strain. This distributed, non-localized strain\ncoordination effectively prevents the concentration of plastic instability\nwithin narrow regions, thereby suppressing necking formation. Consequently,\nthe observation of ‘neck-free’ deformation supports our proposed\nmechanism where domain transformation dominates and coordinates plastic\ndeformation.”\nIn summary, the macroscopic evidence we present confirms the consistency of the\n‘neck-free’ phenomenon. Combined with an in-depth discussion of the underlying\nmechanism, we have demonstrated that domain rotation mediated by Ag ions\nhopping constitutes a robust mechanism capable of efficiently transferring plastic\ndeformation from the nanoscale to the macroscale, resulting in uniform large\nplastic deformation.\n2. Figure 3c presents a strain field map obtained through geometric phase analysis\n(GPA). The accuracy of GPA is highly dependent on the selection of the reference area\nand the correct identification of the unstrained region. I recommend that the authors\nexplicitly label the reference area used for GPA calculations in the Figure 3c illustration.\nAdditionally, line scan profiles of the strains (ε , ε ) should be provided to\nxx yy\nquantitatively demonstrate the magnitude of strain variation and distribution width\nacross domain boundaries, rather than relying solely on qualitative color contrasts.\nAuthor Reply: We thank you for this insightful suggestion regarding the Geometric\nPhase Analysis (GPA). We have now performed the requested quantitative analysis,\nwhich has provided deeper insights into the deformation mechanism.\n1. As suggested, we have specified the reference region used for GPA calculations in\nthe Figure caption for Figure 3c in revised manuscript. “The reference region is\nselected from the unstrained area (top-left corner, as outlined by the red rectangle)\nof the [021] to ensure computational accuracy.” (line 563-565)\nOD\n2. We have added a new Figure 3d, which presents the line scan profiles of the strain\ncomponents (εₓₓ, εὓὓ, ε ) across the domain boundary. The position of the scan is\nxy\nindicated by the blue dashed line in Figure 3c. It’s Figure caption in revised\nmanuscript. “Strain profiles across the domain boundary. Line profiles of the strain\ncomponents (εₓₓ, εὓὓ, εₓὓ) measured along the path from [021] to [021] in c.”\nOD RD\n(line 565-567). And We have added the following corresponding paragraphs to the\nmain text in revised manuscript (lines 188-194): “The resulting strain distribution,\nmapped by geometric phase analysis (GPA) in Figure3c and quantified in Figure\n3d, provides direct evidence of how strain is accommodated under the mechanism.\nThe ~92.2° rotation effectively releases the elastic strain, as seen in the relaxation\nof the εₓₓ component from ~ -9.3% in the [021] to ~ -2.8% in the [021] . Based\nOD RD\non the hopping model, the predicted tensile deformation along the main stress\ndirection is ~17.6%, which aligns with the maximum strain observed in the bulk\ntensile tests (Supplementary Fig. 2).”\nIn summary, the GPA analysis depicts a coherent picture where stress-driven Ag ions\nmigration initiates domain rotation, which concurrently achieves macroscopic strain\nrelaxation (evidenced by the drop in εₓₓ) and microscopic strain accommodation\n(evidenced by the fluctuating shear strains). This unique, reconfiguration-based\nmechanism is fundamentally distinct from dislocation slip and underlies the\nhomogeneous, necking-free plasticity of Ag Te.\n2\n3. The manuscript mentions that \"a 2% strain\" was applied in the DFT calculations to\ndemonstrate the reduction of Ag ion migration barriers. However, the type of applied\nstrain (e.g., uniaxial, biaxial, or volumetric) and its crystallographic direction are not\nspecified. To strengthen the correlation between the computational models and the\nexperimental tensile stress conditions, it is crucial to clarify these parameters.\nAuthor Reply: We thank you for raising this important point regarding the specification\nof the applied strain in our DFT calculations. You are absolutely correct that clarifying\nthe nature of the strain is essential for establishing a direct correlation between our\ncomputational models and the experimental conditions.\n1. In response to this comment, we have revised the manuscript to explicitly state the\nstrain parameters. Line 573-577: “The 2% tensile strain was applied within\nthe (100) plane, which is the primary shear plane corresponding to the direction of\nthe applied tensile stress in the in-situ TEM experiments. This specific loading\ncondition was chosen to directly mimic the stress state that activates the ionic-hop-\nmediated domain rotation observed experimentally.” And line 201: “within\nthe (100) plane.”\n4. I would appreciate additional details on the relationship between thermoelectric\nproperties and plasticity mechanisms. How does plastic deformation influence its\nthermoelectric properties?\nAuthor Reply: We thank you for raising this critical point regarding the interplay\nbetween plastic deformation and thermoelectric properties. We agree that this is\nessential for assessing the material's application potential. While our study focuses on\nelucidating the atomic-scale deformation mechanism, we can address this question by\ndrawing upon direct experimental evidence from our related, systematic investigation\non the same material system.\n1. In our prior work [DOI:10.1016j.mtphys.20233.101051, \"Highly deformable\nAg Te₁₋ₓSeₓ-based thermoelectric compounds, Materials Today Physics, 33, 101051\n2\n(2023)\"], we comprehensively studied the Ag Te ₁₋ₓSeₓ system and demonstrated\n2\nthat exceptional plastic deformability and high thermoelectric performance can\nindeed coexist. The key evidence from that study includes: The Ag Te ₁₋ₓSeₓ(x=0-\n2\n0.2) compounds were shown to exhibit compressive strains exceeding 24% and\neven tensile strains up to 43% at room temperature, while simultaneously\nmaintaining a high thermoelectric Figure of merit, with ZT values reaching up to\n0.61 at 380 K. This ZT value surpasses that of most near-room-temperature flexible\nsemiconductors.\n2. Therefore, this result from our referenced study provides a compelling precedent. It\nconfirms that the class of materials to which our subject Ag Te belongs can sustain\n2\nthe functional properties required for thermoelectricity even after undergoing\nsubstantial plastic deformation. This strongly supports the feasibility of our\nproposed mechanism as a viable pathway for developing deformable inorganic\nthermoelectric.\nWe have now incorporated a discussion of this highly relevant finding into the revised\nmanuscript (lines 244-249) to directly address the relationship between plasticity and\nthermoelectric performance, as suggested. “The compatibility of this unique plasticity\nmechanism with functional properties is a key advantage. Prior studies on closely\nrelated Ag Te₁₋ₓSeₓ compounds have demonstrated that extraordinary room-\n2\ntemperature plastic deformability can coexist with a high thermoelectric Figure of merit\n(ZT > 0.6)17. This is because chemical stoichiometry and overall chemical bonding\npreserve during deformation, avoiding introduction of the detrimental defects that\nwould severely degrade electronic transport.”\n5. Figure. 1b: Please state the strain rate and direction of stretching used for the bulk\ntensile test. And Figure. 3a: The purple rectangles highlighting the lattice distortion\nshould be more clearly labeled and described in the caption.\nAuthor Reply: We thank you for these careful observations. We have revised the\nmanuscript and Figures accordingly to provide the missing details and improve clarity.\n1. We apologize for this omission. This information has now been added to the caption\nof Figure 1 in the revised manuscript (line 541-542). “The strain rate for the bulk\ntensile test was 0.2 mm·s⁻¹. And the tensile direction was along the longest\ndimension of the dog-bone-shaped sample.”\n2. We agree that the labeling could be clearer. We have now revised the caption for\nFigure 3a to explicitly state (line 558-562): \"The purple rectangles highlight the Te-\nsublattice in the original domain ([021] ) and the rotation domain ([021] ),\nOD RD\nillustrating the anisotropic deformation of the Te-sublattice, referring to elongation\nalong the tensile axis (F ̅ ) direction and compression along the transverse\n[021 ]\ndirection (F ) direction.\"\n[201]\nWe believe these revisions have fully addressed yours concerns and thank them for\nhelping us improve the clarity of our presentation.\n6. The manuscript measured the deformation of the Te sublattice (0.34 nm → 0.40 nm)\nvia HAADF-STEM images (Figure 3a). The contrast in HAADF images depends on\nthe total scattering power of atomic columns (related to the square of atomic number\nand atomic count). In the [021] orientation of Ag2Te, the atomic structure comprises\nmixed atomic columns composed of both Ag and Te atoms, as well as pure Ag atomic\ncolumns. Bright spots in the image correspond to mixed columns rich in Ag atoms\n(scattering superposition from multiple Ag atoms), not pure Te atomic columns. If\nspacing measurements were inadvertently taken between two mixed columns or\nbetween a mixed column and a Te column, the measured deformation would not reflect\npure Te sublattice deformation, and the measurement accuracy would be questionable.\nAuthor Reply: We thank you for this profound and expert comment regarding the\ninterpretation of HAADF-STEM images. You correctly highlight a critical issue in the\nanalysis of complex structures like Ag Te. We agree that unambiguous identification of\n2\natomic column species is paramount. We have taken the following steps to address this\nconcern and substantiate our measurements.\n1. To unequivocally identify the atomic columns, we performed image\nsimulations based on the known crystal structure of Ag Te in the [021] zone axis.\nthe revised SI). The captions are revised (line 134-141 in revised SI):\n“Supplementary Fig. 7: Atomic-scale comparison between experimental\nHAADF-STEM image and simulated structure at the domain boundary. (a)\nExperimental HAADF-STEM image of the boundary between the [021] and\nOD\n[021] . Red circles indicate Te-Ag mixed columns, blue circles indicate pure Ag\nRD\ncolumns. (b) Corresponding simulated HAADF image. The spacing between the\nTe-Ag mixed columns increases from 0.34 nm to 0.40 nm across the domain\nboundary, matching the experimental observation in Figure. 3a. This anisotropic\ndimensional change of the Te-sublattice under stress drives the Ag ions hopping that\nmediates the domain rotation.”. This simulation provides the definitive reference\nthat our experimental image (Figure. 3a) is correctly interpreted, confirming that\nthe spacing we measured (0.34 nm to 0.40 nm) is between the two Te-Ag mixed\ncolumns.\n2. We clarify that while these are \"mixed columns,\" their positions in the [021]\nprojection are defined by the rigid Te-sublattice framework. The highly mobile Ag\nions reside within the interstitial sites of this framework. Therefore, a change in the\nspacing between these two fixed, Te-defined positions directly reflects the\ndeformation of the Te-sublattice itself.\n3. The measured deformation is fully consistent with our proposed mechanism. The\nhopping of Ag ions is triggered by and serves to stabilize the deformation of the Te-\nsublattice. It is physically intuitive that the Te-Te framework spacing would change\nsignificantly during such a large (~92.2°) lattice rotation. Our measurement\nquantitatively captures this change.\nIn summary, through definitive image simulation, we have verified that the measured\nlattice spacing change accurately reflects the deformation of the Te-sublattice. Yours\ninsightful comment has allowed us to strengthen this fundamental aspect of our analysis.\nWe have incorporated the image simulation results into revised manuscript (line 177-\n180) “The spacing between the atomic columns identified as Te-dominated (specifically,\nTe-Ag mixed columns) by image simulation (Supplementary Fig. 7), substantially\nincreases from 0.34 nm to 0.40 nm along the tensile axis, while being compressed\ntransversely.”\n7. The manuscript has described a mechanism involving “Ag ion hopping stabilizing\nthe deformed Te sublattice.” But can this be refined into a more universal theoretical\nmodel or physical picture? For example, can this material be regarded as a “semi-solid”\nor “pseudo rheological” system, where the rigid Te sublattice framework undergoes\nplastic relaxation by the flow of ions.\nAuthor Reply: We thank you for this exceptional and forward-looking suggestion. We\nagree that refining our discovered mechanism into a universal theoretical model, such\nas a \"semi-solid\" or \"pseudo-rheological\" system, represents a fascinating and\nimpactful direction for the entire field of flexible inorganic semiconductors. In direct\nresponse to your insight, we have formulated the following generalized physical picture\nbased on our findings in Ag Te:\n2\n1. The material can be conceptualized as a dynamic composite: a rigid, covalently-\nbonded Te-sublattice framework that defines the crystal structure, permeated by\na quasi-fluid sub-lattice of mobile Ag ions.\n2. Plasticity is achieved through a stress-activated, cooperative process: macroscopic\nstress induces elastic deformation of the rigid Te framework, which in turn creates\na driving force and lowers the energy barrier for the Ag ions to hop. The rapid ion\nmigration then stabilizes the deformed framework, allowing for massive plastic\nflow without fracture. In other words, the ions \"lubricate\" the reconfiguration of the\nrigid lattice.\nWe consider this model to be a powerful and predictive framework. However, after\ncareful consideration, we have decided not to incorporate this broader theoretical\nextrapolation into the main text of the current manuscript. We believe that asserting\nsuch a universal model in the manuscript would require direct experimental evidence\nfrom a range of other compounds, which is a significant undertaking that constitutes\nthe focus of our ongoing and future research.\nReviewer #2 (Remarks to the Author):\n1. At the very beginning of the Abstract, the authors highlighted the importance of silver\nsulfide and emphasized that the origin of plasticity in such materials remains poorly\nunderstood. However, this work focuses on Ag Te, not Ag S. Moreover, the\n2 2\nmechanisms of plasticity in Ag S or Ag S-Ag Te alloys have been well investigated by\n2 2 2\nmany studies, such as [Shi et al., Nat. Mater. 2018, 17, 421-426; Yang et al., Adv. Mater.\n2021, 2007681; Wang et al., Adv. Funct. Mater. 2023, 2300189; Wang et al., Nat. Mater.\n2025, doi.org/10.1038/s41563-024-02112-7; Hu et al., The Innovation, 2022, 3,\n100341]. The authors should clarify the differences between the Ag+ hopping\nmechanism and those reported in the literature, and explain why the new mechanism\ntakes over.\nAuthor Reply: We sincerely thank you for this critical observation and for providing\nthese highly relevant references.\n1. We apologize for the lack of precision in our original abstract, which used the broad\nterm \"silver sulfide\" and inadvertently obscured the focus of our work on Ag Te.\nfocus on Ag Te and silver chalcogenides as a broader class: “The discovery of silver\n2\nchalcogenides ductile semiconductors with high room-temperature plasticity holds\nsignificant promise for the development of bendable thermoelectric and electronic\ndevices. However, the atomic-scale origins of their plasticity, ranging from\ndislocation slip to sublattice amorphization, remain diverse and material-specific.\nHere, we report a distinct deformation mechanism in Ag Te through stress-driven\n2\nand ionic-hop-mediated domain rotation. By in-situ scanning/transmission electron\nmicroscopy (S/TEM), we directly observe the hopping of Ag ions to adjacent\nvacancies stabilizes the deformed Te-sublattice and facilitates a coordinated ~92.2°\nlattice rotation that accommodates substantial plastic strain. This mechanism, which\npreserves long-range crystallinity, contrasts with both traditional dislocation-\nmediated plasticity and stress-induced amorphization pathways. Combined with its\nexcellent thermoelectric performance (ZT value of ~0.67) at room temperature,\nAg Te emerges as a promising flexible electronic material.”\n2\n2. More importantly, we are grateful for the opportunity to clarify the fundamental\ndistinction between the mechanism we report in Ag Te and those previously\n2\nestablished for Ag S and its derivatives (e.g., Ag Te₁₋ₓSₓ). The cited literature\n2 2\nreveals that plasticity in Ag S-based systems primarily arises from one of two\n2\nestablished paradigms:\n1) Metallic-like slip on wavy planes due to relatively non-directional bonding [Shi\net al., Nat. Mater. 2018].\n2) Sublattice amorphization, where the entire anionic (Te/S) framework becomes\ndisordered under stress, mediated by the fluid-like diffusion of Ag ions [Wang\net al., Nat. Mater. 2025; Hu et al., The Innovation, 2022].\n3. In stark contrast, our work on Ag Te uncovers a distinct mechanism: Stress-Driven\n1) In Ag Te (our work): The Te-sublattice remains crystalline but undergoes a\n2\nlarge, coordinated lattice rotation of ~92.2°. This reorientation is enabled by\ndiscrete, stress-induced hopping of Ag ions between adjacent tetrahedral sites,\nwhich stabilizes the deformed Te framework. The process is localized, forming\na clear domain boundary.\n2) Our mechanism does not rely on widespread dislocation slip nor on the\namorphization of the structural framework. Instead, it demonstrates\na crystalline-to-crystalline transformation via ionic hopping, a paradigm that\nhas not been reported before in this material system.\nTherefore, our work does not merely apply a known mechanism to a new material;\nit reveals a novel deformation mode that significantly expands the understanding of\nplasticity in inorganic semiconductors. We have now incorporated a detailed discussion\nand comparison with these key references in the main text section of our revised\nmanuscript to highlight this conceptual advance (line 55-58). “More recent work on\nsilver chalcogenides has revealed alternative pathways; for instance, plasticity in Ag S\n2\nhas been linked to metallic-like bonding and wavy slip planes12, while research on\nAg Te₁₋ₓSₓ solid solutions has uncovered a mechanism involving stress-induced\n2\nsublattice amorphization stabilized by mobile Ag ions19,46.”\n2. In the main text, the authors should (but they did not) provide an overview of previous\nresearch progress on the plasticity of Ag Te, nor did they include any description related\n2\nto thermoelectric properties.\nAuthor Reply: We thank you for the kind suggestions. We agree that providing a clear\noverview of the research context for Ag Te is crucial. In the original manuscript, this\n2\ninformation was provided but somewhat dispersed. In the revised version, we have now\nconsolidated and significantly strengthened this overview to directly address your\nconcern.\nThe revisions were implemented at two key points to frame our study effectively:\n1. In the Introduction (Lines 63-73), we have now introduced Ag Te by explicitly\n2\nhighlighting its dual identity as both a plastic and thermoelectric material. The\nspecific statement – “Ag Te is a semiconductor with both ionic and covalent\n2\nbonding characteristics48–54 that exhibits remarkable room-temperature\nplasticity17,55 and is concurrently recognized as a promising near-room-temperature\nthermoelectric material17,50,55–58. The plasticity enhancement strategies for Ag\nhave continuously developed to tackle the inherent brittleness bottleneck of\ninorganic semiconductors, progressing from nano-structuring (e.g., nanowires47) to\nmicro-engineering (e.g., domain boundaries55) and down to atomic-scale\nmechanisms (e.g., sublattice amorphization46). These mechanisms not only\nsignificantly improve ductility (achieving strains up to 75.7% in nanowires and\ntensile ductility of 10,150% in bulk materials) but also optimize thermoelectric\nperformance through phonon scattering (with ZT values enhanced to 0.6-2.2).” – is\nplaced to pose the core scientific question that our manuscript addresses.\nFurthermore, by contrasting it with the more established ductility of high-S\nmaterials, we clearly signal that Ag Te represents a distinct and less understood case,\n2\nthereby justifying the need for our investigation.\n2. In the Discussion section (Lines 250-258), we have added a comparative analysis\nthat directly positions our newly discovered mechanism within the existing\nliterature. “Our discovered mechanism of ionic-hop-mediated domain rotation\nfurther distinguishes itself from other plasticity pathways in Ag Te. For instance, in\n2\non the (001) plane, followed by Ag precipitation under extreme stress47. In contrast,\nthe plasticity in our bulk Ag Te samples is achieved without phase separation or\n2\ntwinning, but through a coherent lattice rotation. This distinction underscores the\nmaterial-specific nature of plastic deformation and highlights the unique advantage\nof the mechanism in preserving both crystallinity and chemical stoichiometry, a\nprerequisite for maintaining optimal thermoelectric function.” By citing and\ncontrasting our findings with the recent work on plasticity in Ag Te nanowires\n2\n(which involves twinning and phase separation), we accomplish several goals:\n1) It demonstrates scholarly awareness of the field's progress.\n2) It sharply delineates the novelty of our \"ionic-hop-mediated domain rotation\"\nmechanism by highlighting its key advantage: the preservation of crystallinity\nand stoichiometry.\n3) It directly links the mechanical mechanism to thermoelectric functionality,\narguing that our mechanism is inherently more compatible with maintaining\ngood electronic transport properties, which is a central theme of our work.\nWe believe these revisions provide a comprehensive and logical foundation for our\nstudy, clearly outlining the prior progress on Ag Te and seamlessly integrating its\n2\nthermoelectric relevance.\n3. The introduction regarding previous studies on plastic semiconductors is overly\ngeneral. At present, numerous plastic semiconductors have been reported, and a variety\nof plasticity mechanisms are proposed. Yet, the authors simply attribute them to\ndislocation motion and stacking fault mechanisms.\nAuthor Reply: We thank you for the kind suggestions as to be more specific in plasticity\nmechanisms. We agree that the field has moved beyond attributing plasticity solely to\ndislocation motion and stacking faults, and a variety of distinct mechanisms have been\nreported.\nWe have substantially revised the introduction to go beyond a general description and\nnow specifically cite and differentiate between key mechanistic paradigms. As\nhighlighted in the second paragraph of the revised introduction (lines 45-62): \" Flexible\nsemiconductors have received a lot of attention due to their potential in the development\nof bendable, stretchable and wearable electronic devices, such as thermoelectric\ngenerators and flexible transistors1–9. Notably, several inorganic semiconductors,\nprimarily chalcogenides, have been discovered to exhibit significant room-temperature\nplasticity1,10–24. This unique property enables the direct integration of robust electronic\ncomponents into flexible systems, bypassing the need for complex film-on-substrate\narchitectures25–31.\nDespite these promising prospects, the atomic mechanisms responsible for large\nplastic deformation in these inherently brittle materials are diverse and not fully unified.\nEarly studies often attributed plasticity to dislocation motion and stacking faults17,32–45.\nMore recent work on silver chalcogenides has revealed alternative pathways; for\ninstance, plasticity in Ag S has been linked to metallic-like bonding and wavy slip\n2\nplanes12, while research on Ag Te₁₋ₓSₓ solid solutions has uncovered a mechanism\n2\ninvolving stress-induced sublattice amorphization stabilized by mobile Ag ions19,46. In\nAg Te nanowires, plasticity is attributed to the synergistic effects of dislocation\n2\nemission, slip band formation, deformation twinning, and Ag nanobridges47. This\ndisparity indicates that a one-size-fits-all model is insufficient, and material-specific\nmechanisms await discovery.”\nThis revision explicitly acknowledges the existence of specific, non-dislocation-based\nmechanisms—namely, slip in metallic-like frameworks and sublattice amorphization—\nthereby providing the concrete overview of diverse mechanisms as requested. This\nsetup directly underscores the novelty of the third, distinct mechanism (ionic-hop-\nmediated domain rotation) that we report in Ag Te.\n2\n4. Are the rotation domains twins of the original domains? It has been demonstrated in\nthis work [Wu et al., Adv. Funct. Mater. 2025, 35, 2423014] that many deformation\ntwins form along the (001) plane, which inhibits crack initiation. I do not see clear\nevidence of Ag hopping. It could be a simple structural deformation and twinning-\ninduced plasticity.\nAuthor Reply: We thank you for raising this important point regarding the nature of the\nrotation domains and for directing us to the highly relevant study by Wu et al. We agree\nthat deformation twinning is a crucial plasticity mechanism in nanomaterials, and the\nwork by Wu et al. demonstrates its role in Ag Te nanowires, where twins on the (001)\n2\nplane inhibit crack propagation. However, the mechanism we report in the bulk Ag Te\n2\nsamples is fundamentally distinct from the deformation twinning observed by Wu et al.,\nfor the following reasons:\nIn Wu et al., the formation of deformation twins on the (001) plane is characterized\nby a specific mirror symmetry relationship between the parent crystal and the twin,\nwhich is a defining feature of twinning. In our work, the ~92.2° reorientation forms a\nrotation domain, not a twin. The boundary between the original domain ([021] ) and\nOD\nthe rotation domain ([021] ) is coherent but does not obey a twin orientation\nRD\nrelationship. This is a different crystallographic relation, driven by a unique atomic-\nscale process. Accordingly, we have incorporated intuitive evidence and descriptions in\nboth the revised main text and Supplementary Information, as follows: line 130-140 in\nrevised manuscript: “The FFT patterns from the [021] and [021] (Supplementary\nOD RD\nFig. 5a) provide definitive crystallographic evidence that this is a rotation domain, not\na twin. The yellow dashed line in the FFT represents the trace of the (012̅) plane, which\nwould be the mirror plane if this were a deformation twin. This trace is determined\ngeometrically as the line through the FFT center that is perpendicular to the vector\nconnecting the center to the (012̅) diffraction spot. As demonstrated, the diffraction\nspots from the [021] (red circles) do not have a mirror symmetry to these spots from\nRD\nthe [021] (blue circles) across this line. Instead, the entire diffraction pattern from the\nOD\n[021] is rotated by ~92.2° with respect to that of the [021] (Supplementary Fig. 5b).\nRD OD\nThe absence of such mirror symmetry confirms the non-twinned nature of the domain\nboundary.” And line 93-103 in revised SI “Supplementary Fig. 5: Crystallographic\nevidence for rotation domains versus deformation twins. (a) HAADF-STEM image\nof a typical domain boundary with the corresponding Fast Fourier Transform (FFT)\npatterns from the [021] (Ⅰ) and [021] (Ⅱ). The yellow dashed line in the FFT\nOD RD\npatterns indicates the trace of the (012̅) plane, which would be the mirror plane if this\nwere a deformation twin. The absence of mirror symmetry of the diffraction spots (e.g.,\nthe (012̅) spots marked by circles) across this line rules out a twin relationship. (b)\nOverlaid FFT pattern from both domains after center alignment. The (012̅) spot from\n[021] (blue circle) and its counterpart from [021]\nOD RD\n(red circle) are related by a ~92.2° rotation about the central axis, rather than by\nmirror symmetry. This rotation of the entire diffraction pattern confirms the formation\nof a rotation domain, not a deformation twin.”\n3. Regarding to the Ag ions hopping, we have provided the following direct evidence\nin the revised manuscript:\n1) Figure 3a (the experimental STEM image showing the interface of the rotation\ndomain) provides a direct atomic-scale illustration of the mechanism. The\ndeformation leads to an anisotropic distortion of the Te-sublattice (elongation\nalong one axis, compression along the other), creating a driving force for ion\nhopping.\n2) The model drawn from the experimental STEM image (Figure. 3b,\nSupplementary Fig. 6b) shows that an Ag ion hops from a compressed\ntetrahedron into an adjacent, expanded tetrahedral site (which is a pre-existing\nvacancy in the structure). This hop rotates the entire plane of Ag-\nvacancies by ~92.2°, which is the direct cause of the domain reorientation.\nThis process is not a simple shear (as in twinning), but a stress-induced,\ncoordinated ionic migration that stabilizes the new lattice configuration.\n3) The first-principles calculations (Figure. 4a-b) provide quantitative support,\nshowing that the applied lattice strain significantly reduces the migration\nbarrier for Ag ions, making this hopping process energetically favorable under\nthe stress.\n4. The work by Wu et al. and our study highlight the rich plasticity of Ag Te across\n2\ndifferent scales and forms:\n1) Wu et al. (Nanowires): Mechanism involves dislocation slip, (001) deformation\ntwinning, and eventual Ag precipitation under very high local stress (~2.5 GPa).\n2) Our work (Bulk Samples): We observe none of these features. There is no sign\nof Ag precipitation (EDS in Supplementary Fig. 4b confirms stable\nstoichiometry), and the dominant feature is the coherent ~92.2° rotation domain,\nwhich we show originates from ion hopping.\nIn conclusion, while we acknowledge deformation twinning as an important\nmechanism—especially in low-dimensional systems—the evidence in our work\nunequivocally supports ionic-hop-mediated domain rotation as the dominant\nmechanism in the bulk Ag Te samples. This mechanism is distinct from both traditional\n2\ntwinning and the Ag precipitation pathway, representing a new paradigm for plasticity\nin materials with mobile ions.\n5. The DFT calculated migration barrier for Ag shows minimal variation. More details\nabout the selection of the NEB path should be provided and compared.\nAuthor Reply: We thank you for this question, which allows us to clarify the physical\nbasis for our NEB path selection and the significance of the calculated migration\nbarriers.\n1. The two Ag⁺ migration paths (Path 1 and Path 2) shown in Figure 4a were not\nchosen arbitrarily. They were chosen from the atomic-scale experimental\nobservations. As detailed in the main text and illustrated in Figure 3b, the proposed\ndeformation mechanism involves the hopping of an Ag ion from a compressed\ntetrahedron into an adjacent, expanded tetrahedral site (which is a pre-existing\nvacancy in the structure). Path 1 and Path 2 represent the two shortest and most\nsymmetric hopping trajectories between these specific crystallographic sites that are\ninvolved in the domain rotation process. Our path selection is therefore mechanism-\ndriven, designed to directly test the feasibility of the atomic process we observed\nexperimentally.\n2. You correctly note the minimal variation in the migration barriers (~0.47 eV for\nboth paths without strain). We argue that this result is highly significant and\nconsistent with our model:\n1) This near-identical energy cost indicates that the Ag ion migration is not highly\nsensitive to the specific crystallographic direction within the plane of the\nvacancy-concentrated layer. This low anisotropy for ion hopping is precisely\nwhat facilitates the cooperative ion migration required for large-scale domain\nrotation, as it allows multiple equivalent paths for ions to rearrange in response\nto stress.\n2) The key physical insight, as we emphasize, is not a large difference between\npaths, but the fact that applied strain universally and significantly lowers the\nbarrier for both paths (from 0.47 eV to 0.43 eV under 2% strain). This uniform\nreduction demonstrates that the mechanical deformation softens the lattice for\nion migration, making the process thermodynamically favorable. This strain-\ninduced softening is the core of our proposed mechanism.\nTo further address your concern, we have now included in the ‘Supplementary Text for\nDFT calculation’ in revised manuscript (line 321-327) an additional note on our NEB\nmethodology. “The specific Ag migration paths investigated by the CI-NEB method\n(Figure. 4a) were selected to directly test the atomic-scale mechanism obtained from\nthe experimental observations (Figure 3b). The initial and final states were defined as\nthe configurations with the Ag ions residing in two adjacent, symmetry-equivalent\ntetrahedral sites that share a common vacancy. The calculated paths (Path 1 and Path 2)\ncorrespond to the most geometrically straightforward hopping trajectories between\nthese sites, which are integral to the domain rotation process.”\nIn summary, our DFT calculations are tightly coupled to our experimental findings. The\nselected paths are physically motivated, and the calculated barriers and their strain\ndependence provide robust support for the plausibility of the Ag ions hopping\nmechanism.\n6. The ZT values reported in this manuscript are not high among plastic semiconductors.\nFurthermore, the comparison of ZT in Figure 4d is selective, which does not represent\nthe state-of-the-art of ductile thermoelectrics. The authors should either stick to the\nmaximum ZT value reported in each work or make the comparison at the same\ntemperature. Alternatively, they can also compare the temperature-dependent ZT curves.\nIn addition, corresponding references to the data in Figure 4d must be indicated clearly.\nAuthor Reply: We thank you for this critical comment regarding the thermoelectric\nperformance comparison. We agree that the ZT value of Ag Te, while promising, is not\n2\nthe highest among all ductile semiconductors. We have revised our presentation to\naddress this point.\n1. As you imply, the central claim of our manuscript is not to report a record-breaking\nZT, but to uncover a novel plasticity mechanism (ionic-hop-mediated domain\nrotation). The thermoelectric performance is presented as a crucial, complementary\nproperty that demonstrates the material's potential as a versatile functional material\nfor flexible electronics. We have now revised the text in the “Compatibility of\nPlasticity and Thermoelectric Properties” section and the Figure caption of Figure.\n4d to consistently emphasize that Ag Te is a model system that uniquely combines\n2\nthis new deformation mechanism with good thermoelectric performance. The\nmodifications in revised manuscript are as follows: line 231-232: “The practical\npotential of a functional semiconductor is determined by the synergy between its\nmechanical and electronic properties.” And line 579-582: “This comparison\nhighlights the competitive thermoelectric performance of Ag Te, which, when\n2\nintegrated with its novel plasticity mechanism, positions it as a promising model\nsystem for flexible electronics.”\n2. We fully agree that a fair comparison is essential. We have completely remade\nFigure 4d to compare the ZT values of all ductile semiconductors at the same\ntemperature of ~400 K, using the maximum reported ZT at that temperature for\neach material. This provides a transparent and equitable benchmark. And all data\npoints in the new Figure 4d are now accompanied by clear and complete citations\nin the Figure caption. Line 238-243 in revised manuscript: “A direct comparison\nat a uniform temperature of ~400 K9,30,37,60–69 (Figure. 4d) confirms that this ZT\nvalue is comparable to other state-of-the-art room-temperature ductile\nsemiconductors. This demonstrates that Ag Te successfully combines a unique\n2\ndeformation mechanism with high thermoelectric performance, suggesting its\npotential for flexible thermoelectric applications.”\nRevised Figure 4 (d) Comparison of the thermoelectric figure of merit (ZT) at a\nuniform temperature of ~400 K for representative room-temperature ductile\nsemiconductors. This comparison highlights the competitive thermoelectric\nperformance of Ag Te, which, when integrated with its novel plasticity mechanism,\n2\npositions it as a promising model system for flexible electronics. Data sources:\nRefs. [9, 23, 30, 37, 59-68].\nWe believe these revisions have strengthened our manuscript by providing a fair\nperformance comparison while rightly positioning the discovery of the new plasticity\nmechanism as the cornerstone of our work.\nReviewer #3 (Remarks to the Author):\n1. The current evidence for “Ag ions hopping” remains insufficient. Ionic conductivity\nmeasurements would offer additional experimental support. In addition, as the exact\nmigration path of Ag ions is unknown, how to define path 1 & 2? On the other hand,\nreferences 47-50 do not state that monoclinic Ag Te contains ionic bonding. Please\n2\nprovide more evidence from experiments or theoretical calculations.\nAuthor Reply: We thank you for raising the important point regarding evidence for Ag\nions hopping. We have strengthened our argument through additional theoretical\nanalysis and by contextualizing our electrical measurements within the established\nliterature, as detailed below.\n1. Regarding the microscopic mechanism of Ag ions hopping, the study provides\ntripartite evidence through atomic-scale experimental observations, structural\nmodel reconstruction, and first-principles calculations: Strain-induced anisotropic\ndistortion of the Te sublattice (Figure 3a) creates the driving force for Ag ions\nhopping; the model constructed based on experimental images (Figure 3b)\ndemonstrates that Ag ions hopping from compressed tetrahedra to adjacent\nvacancies cause an approximately 92.2° rotation of the Ag-vacancy plane, thereby\nenabling domain reorientation; theoretical calculations (Figures 4a-b) further\nconfirm that lattice strain significantly reduces the migration energy barrier for Ag\nions, validating the feasibility of this stress-driven cooperative ion migration\nprocess from an energetic perspective.\n2. Although direct measurement of ionic conductivity in Ag Te is challenging due to\n2\nits high electronic conductivity (a known characteristic of this narrow-gap\nsemiconductor), the temperature-dependent total conductivity measurements\n(Supplementary Fig. 10a) provide supportive evidence. The increase in conductivity\nwith temperature is characteristic of a thermally activated process. In mixed\nconductors like Ag Te, this behavior reflects the contribution of both electrons and\n2\nmobile ions. This aligns with the well-documented high ionic mobility in Ag Te and\n2\nrelated compounds, as reported in prior studies [e.g., Kurosaki et al., J. Alloys\nCompd. 2005, ref. 49].\n3. Paths 1 and 2 were not arbitrary. The two Ag⁺ migration paths (Path 1 and Path 2)\nshown in Figure 4a were chosen based on the atomic-scale experimental\nobservations. As detailed in the main text and illustrated in Figure 3b, the proposed\ndeformation mechanism involves the hopping of an Ag ion from a compressed\ntetrahedron into an adjacent, expanded tetrahedral site (which is a pre-existing\nvacancy in the structure). Path 1 and Path 2 represent the two shortest and most\nsymmetric hopping trajectories between these specific crystallographic sites that are\ninvolved in the domain rotation process, as directly implied by our atomic model in\nFigure. 3b. To illustrate this, we have amended the description in lines 196-198 of\nthe revised manuscript as follows: “We calculated the migration barriers for the two\nmost probable paths (Path 1 and Path 2, Figure. 4a) connecting adjacent tetrahedral\nsites involved in the domain rotation.”\n4. You are correct that references 47-50 alone do not fully establish the ionic bonding\ncharacter. To address this crucial point conclusively, we have supplemented the\nreferences by adding two new citations (refs. 52-53) which specifically discuss the\nmixed ionic-covalent bonding nature in monoclinic Ag Te based on first-principles\n2\ncalculations, thereby solidifying the foundational premise of our proposed ion-\nhopping mechanism.\nIn summary, while a direct ionic conductivity measurement is experimentally\nprohibitive, the combination of our quantitative Bader charge analysis (confirming\nionic bonds), the thermally activated transport behavior, and the well-established\nliterature on Ag-ion mobility in this material system, collectively provide robust and\nmulti-faceted support for the feasibility of the Ag ions hopping mechanism.\n2. The manuscript attributes plasticity of Ag Te to the formation of rotation domains.\nclarified. In addition, other defects, including dislocations, twins, and staking defects,\nare not studied or discussed.\nAuthor Reply: We thank you for these questions, which allow us to clarify the\nobservation in our work. The nature and formation mechanism of the rotation domains\nare, in fact, the central focus of our study, and we have provided detailed explanations\nin the revised manuscript.\n1. As detailed in the “The microstructural mechanism of room-temperature plasticity”\nand “Atomic mechanism of room-temperature plasticity” sections, the rotation\ndomains are crystallographic regions that have undergone a ~92° lattice\nreorientation relative to the original matrix. They are not deformation twins, as\ndefinitively proven by the uniform rotation of the entire FFT pattern\n(Supplementary Fig. 5), which is inconsistent with a mirror-symmetry relationship.\nTheir formation is directly driven by the applied tensile stress, as evidenced by\ntheir high density near the fracture surface in EBSD maps (Figure. 2c) and their\ngradual formation and evolution during in-situ stretching (Supplementary Video 1-\n3).\n2. The precise formation process is elucidated in Figure. 3 and its associated text (line\n163-180 in the revised manuscript). In brief: the stress induces an anisotropic\ndeformation of the rigid Te-sublattice → this deformation destabilizes Ag ions in\ncompressed tetrahedra → triggering their discrete hopping into adjacent expanded\nvacancies → this collective ion hopping rotates the entire vacancy-concentrated\n(100) plane → leading to the coordinated ~92° lattice rotation that defines the new\ndomain.\n3. You rightly point out the importance of other defects. We have now included an\nexplicit discussion on this matter. As stated in the “Atomic mechanism” section,\nour atomic-resolution HAADF-STEM images and GPA analysis reveal that strain\nis primarily accommodated by the formation of the coherent domain boundaries,\nwith no significant observation of dislocations, twins, or stacking faults in the vast\nmajority of the deformed region. This observation allows us to conclude that\ndomain rotation is the dominant mechanism in this specific material under tensile\nloading. Line 218-224: “Both in-situ and ex-situ microstructural study on the\ndeformed Ag Te samples reveal the deformation is mainly accommodated by the\n2\nformation of rotation domains and domains boundaries. We seldom observe other\ndefects (such as twins, stacking faults and dislocations) in the deformed areas.\nHowever, as dislocations refers to the lattice mismatch, in the boundary of [021]\nRD\nand [73̅6] domains (despite formation of the [73̅6] domains is rare, Figure 2d),\nthere would be complicated dislocations to accommodate the lattice mismatch.”\nLine 226-229: “It is the synergistic interplay between the deformation of the Te-\nsublattice and the subsequent hopping of Ag ions that enables the large, coherent\nlattice rotation, distinguishing it fundamentally from conventional dislocation-\nbased plasticity or deformation twinning.”\n3. The high diffusion coefficient of Te atoms (Figure. S7) is doubtful, in contrast to its\nrigid sublattice characteristic. Taking Ag S as an example, the diffusion coefficients of\nAuthor Reply: We sincerely thank you for raising this important and insightful point.\nYou is absolutely correct that in Ag-based superionic conductors like Ag S, the anion\n2\n(S) sublattice is indeed rigid, and its diffusion coefficient is nearly zero, which is a key\ncharacteristic that our study of the Ag Te system aligns with.\n2\n1. We must first clarify that this is not a computational error, but rather a\ntypographical error in the initial version of the supporting information. We\nerroneously applied the average migration rate label to the silver (Ag) migration\nrate. This oversight resulted in the actual ratio of silver to antimony migration rates\nbeing significantly underestimated (incorrectly labelled as 2.5 times). We have\nnow corrected this in the revised manuscript (Supplementary Fig. 9). The corrected\ndata shows that the Ag migration rate is actually approximately 25 times that of Te.\nThis substantial difference is much more consistent with the physical picture of a\nliquid-like Ag sublattice and a rigid Te sublattice in Ag Te.\n2\n2. To further validate the dynamic behavior of tellurium atoms, we conducted\nadditional molecular dynamics simulations at 773 K. The results clearly\ndemonstrate (as shown in the figure below): the mean squared displacement (MSD)\nof Te atoms eventually saturates after an initial increase, unequivocally indicating\nthat they are confined to lattice sites and exhibit negligibly low diffusivity, with a\nmigration rate approaching zero. In stark contrast, the MSD of Ag atoms show\na linear increase throughout the simulation time with no signs of saturation,\ncharacteristic of liquid-like diffusion.\nRevised Supplementary Fig. 9: Mean squared displacement (MSD) and Diffusion\ncoefficients of Ag and Te ions at 600 K and 773 K, respectively.\nOur supplementary high-temperature data fully corroborates the conclusions drawn\nfrom the cited Ag S system literature. For instance, Balyakin and Sadovnikov (2022)\n2\nexplicitly state that in β-Ag S, ‘Sulphur atoms indeed form a stable body-centred cubic\n2\nlattice,’ exhibiting crystal saturation behavior in their mean square displacement (MSD),\nwhilst ‘silver atoms display liquid-like behavior.’ The findings confirm that in Ag Te,\n2\ntellurium atoms (analogous to Sulphur atoms in Ag S) construct a stable rigid\n2\nframework, whilst silver ions migrate rapidly within this framework as mobile charge\ncarriers. We reiterate our gratitude to you for the incisive insights, which enabled us to\nrectify errors and strengthen the paper's conclusions through supplementary\ncalculations. The revised data and supporting materials have been updated accordingly\nwithin the manuscript.\n4. The tensile results for bulk Ag Te in Figure. 1b and Figure. S2b are contradictory:\nhardening—instead, the stress even decreases after yielding. Such inconsistent\nmechanical responses in the same material should not be caused by sample preparations.\nAuthor Reply: We thank you for this insightful observation regarding the apparent\ndiscrepancy in the tensile curves between Figure. 1b and Supplementary Fig. 2b. You\nis correct that Figure. 1b exhibits a strain-hardening effect, while Figure. S2b shows a\nnearly ideal plastic flow.\n1. First, we would like to assure that both sets of data are authentic and representative\nof the mechanical responses we observed in different bulk Ag Te samples prepared\n2\nunder the same conditions. The variation is a real phenomenon, not an artifact of\nmeasurement error. We attribute this difference to the unique and complex\nplasticity mechanism of Ag Te, which is highly sensitive to the initial\n2\nmicrostructural state of individual samples.\n2. The strain hardening (observed in Figure 1b) is directly linked to the grain\nboundary rotation mechanism. The other sets of experimental observations\n(currently under investigation in a typical sample with smaller size of grains, as\nshown in the picture copied below) reveal that, in some cases, grain boundary\ntransformation does not occur via a single boundary spanning the entire grain.\nInstead, as stress increases, multiple rotating grain boundaries are formed, forming\na stepped distribution of grain boundaries within a single grain. Each new interface\nformation must accommodate a finite amount of strain. As deformation continues,\nthe density of these coherent interfaces steadily increases. They interact and\nimpede the further nucleation and growth of subsequent domains, thereby leading\nto the observed strain hardening phenomenon.\nRevised Figure S1: (a, b) Low- and high-magnification TEM bright-field images\nshowing a high density of parallel lines indicative of coherent domain boundaries.\n(c) High-resolution TEM (HRTEM) micrograph revealing a non-uniform, stepped\ndistribution of newly formed domain boundaries within grain, rather than a single\ncontinuous boundary. The progressive formation of these coherent interfaces\nduring deformation increases their density, which impedes further domain\nnucleation and growth, thereby contributing directly to the strain hardening\nphenomenon.\n3. In the revised manuscript, we have swapped the positions of two stress-strain\ncurves (the plastic flow curve is now presented in the main text, while the strain\nhardening curve appears in the supplementary materials). It must be explicitly\nstated that this adjustment was undertaken solely to align the graphical presentation\nmore closely with our discussion of novel domain rotation mechanisms.\nVariations in initial microstructure—such as local crystal orientation, size of grains,\nthe distribution of pre-existing defects, or internal stress concentrations—from one\nsample to another can preferentially activate the formation of rotation domains in\ndifferent ways. This is consistent with \"variations during the preparation\" causing\ndiscrepancies. And a discussion addressing this has been added in lines 210-218 of the\nrevised manuscript. “Both a strain-softening and strain-hardening effects are observed\nin the macroscopic tensile responses in bulk Ag Te, as shown in Figure. 1b and\nmicrostructure, the domain rotation mechanism could manifest in different modes.\nWhen there forms small number of new domain boundaries in big grains, one may\nobserve the strain-softening effect (as shown in Figure. 1b). When involving the\nsequential nucleation of multiple domain boundaries, their cumulative interactions can\nlead to strain-hardening by resisting further deformation (as shown in Supplementary\nFig. 2b).”\nTherefore, we believe Figures. 1b and Supplementary Fig. 2b collectively capture\nthe spectrum of Ag Te's macroscopic mechanical behaviors. The key conclusion,\n2\nrobustly supported by both macroscopic curves and our in-situ TEM experiments, is\nthat bulk Ag Te possesses remarkable room-temperature plasticity, albeit through a\n2\nrotation-domain mechanism.\n5. In the background, the statement “high-Te materials are typically brittle55” is\nincorrect. Both Ag Te S and Ag Te S are Te-rich but show especially high\n2 0.7 0.3 2 0.6 0.4\nductility. In addition, reference 55 talks about Ag (Se,S), not Ag (Te,S).\n2 2\nAuthor Reply: We thank you for this comment and for ensuring the accuracy of our\nstatements. You is absolutely correct that the original statement was imprecise.\n1. We have revised the relevant sentence in the background section of our manuscript.\nThe updated text no longer makes a generalized claim about \"high-Te materials.\"\nInstead, it now specifically highlights the ductility of high-S materials as a known\nphenomenon and positions Ag Te as a ductile high-Te material, which underscores\n2\nits uniqueness. The current sentence in our revised manuscript (line 73-75) reads:\n“Intriguingly, while high-S materials are generally ductile59, Ag Te stands out as\n2\none of the ductile high-Te materials, suggesting a potentially unique deformation\nmechanism.”\n2. The citation of Reference 55 has also been corrected. We have now used it\nappropriately to contrast the known ductility in high-S systems with the newly\nreported ductility in the high-Te system (Ag Te). As the reference [55] (now the\n2\nref. 59 in revised manuscript), while it discusses Ag (Se,S), the fundamental\n2\nprinciple it establishes—that certain silver chalcogenides with a specific crystal\nstructure (like the body-centered cubic structure in high-S phases) can exhibit\nexceptional ductility—provides a relevant conceptual background.\n6. The author misuses “strain rate” to describe the deformation degree, e.g., “the\naverage tensile strain rate of ~10.6%”. “Strain rate” defines the time derivative of strain\n(s⁻¹) (PRL 100, 025502, 2008).\nAuthor Reply: We sincerely thank you for pointing out this critical error in terminology.\nYou is correct. We mistakenly used \"strain rate\" (which, as rightly noted, is the time\nderivative of strain with units of s⁻¹) when we intended to refer to the total \"strain\" (a\ndimensionless measure of deformation).\nWe have now corrected this oversight throughout the manuscript. Specifically, the\nsentence in question has been revised from:\"...with the average tensile strain rate of\n~10.6%.\" to \"...with an average tensile strain of ~10.6%.\"\nWe appreciate your meticulous attention to detail, which has helped us improve the\nprecision and clarity of our manuscript.\n7. The phrase “Ag+ ions” is wrong. “Ag+” already implies ionic nature and charge of\nsilver, and combining “Ag” with “ions” creates unnecessary repetition. Use either “Ag+”\nor “Ag ions”.\nAuthor Reply: We thank you for this precise correction regarding terminology. You is\ncorrect that \"Ag+ ions\" is redundant, as the \"+\" charge notation already defines the\nspecies as an ion.\nWe have followed your suggestion and revised the text accordingly. The phrase has\nbeen changed to \"Ag ions\" throughout the manuscript to ensure conciseness and\nscientific accuracy.\nWe appreciate your attention to detail in helping us refine the language of our\nmanuscript.\n8. There has recently been a work that reveals Ag-ion diffusion is crucial for the\nplasticity of Ag Te S semiconductors (Nat. Mater. 2025). Is there anything different\n2 1–x x\nor common compared with this work? In addition, the plasticity of Ag Te has been\n2\nreported before (Adv. Mater. 2023, 35, 2302969), and the thermoelectric performance\nof Ag Te in this work is not outstanding compared with the previous work either.\nwith recent literature and the novelty of our work. We appreciate the opportunity to\nclarify the unique contributions of our study.\n1. We are aware of the recent Nat. Mater. 2025 work, which highlights the crucial\nrole of Ag-ion diffusion in the plasticity of Ag Te₁₋ₓSₓ semiconductors. There are\n2\nboth commonalities and distinctions between that work and ours:\n1) Both studies recognize that Ag-ion migration is a key factor enabling plasticity\nin Ag Te-based materials. This aligns with our observation of Ag⁺ hopping\n2\nfacilitating deformation.\n2) Our work focuses specifically on the role of domain boundaries (DBs) and\nreveals a previously unreported mechanism—ionic-hop-mediated domain\nrotation—where Ag⁺ hopping coordinates with large-scale crystalline\nreorientation of the Te-sublattice. In contrast, the Nat. Mater. 2025 work\nprimarily emphasizes Ag-ion diffusion alone as a driver for plasticity, without\nexploring the domain-level structural evolution or its synergy with mechanical\nproperties. Additionally, our study provides direct evidence from in-situ TEM\nand DFT calculations showing how DBs transformation buffer deformation,\nleading to simultaneous enhancement of strength and ductility. Thus, while Ag-\nion mobility is a shared element, our mechanism is distinct in its emphasis on\ndomain rotation and its engineering to realize plasticity.\n2. We acknowledge that room-temperature plasticity in Ag Te has been reported\n2\npreviously (e.g., in Adv. Mater. 2023 manuscript referenced). However, our current\nwork goes beyond mere documentation of plasticity by demonstrating a synergetic\nenhancement of strength–ductility and thermoelectric properties through domain\nengineering. Key advances include:\n1) We achieved a 40% improvement in compressive strength (160 MPa) and a\n200% improvement in fracture strain (16%) compared to domain-free samples,\nalong with superior machinability (e.g., fabrication of micro-legs with cross-\nsections as small as 75 μm × 75 μm). This represents a significant step beyond\nprior reports that focused solely on ductility without strength enhancement.\n2) While the absolute ZT value (0.6 at 400 K) may not be the highest reported for\nAg Te, our work shows a 45% improvement in average ZT due to domain-\n2\ninduced phonon scattering reducing lattice thermal conductivity without severe\ndegradation of electronic properties. This synergistic optimization of\nmechanical and thermoelectric performance is novel and has not been achieved\nin previous studies.\n3) We provide a comprehensive mechanism linking ionic hop to domain rotation,\nwhich is different from conventional dislocation slip or sublattice amorphization.\nIn summary, our work introduces domain boundary engineering as a new strategy to\nconcurrently enhance mechanical and thermoelectric properties in Ag Te, offering\n2\nbroader implications for functional semiconductors. We have revised the discussion\nsection in our manuscript to more explicitly contrast our findings with these related\nworks, ensuring the novelty and contributions are clearly articulated.\nReviewer #4 (Remarks to the Author):\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports.\nThis is part of the Nature Communications initiative to facilitate training in peer review\nand to provide appropriate recognition for Early Career Researchers who co-review\nmanuscripts.\nAuthor Reply: We thank Reviewer #4 for his time and contribution to the peer-review\nprocess of our manuscript. We greatly appreciate and support initiatives like that\nof Nature Communications that provide valuable training and recognition for Early\nCareer Researchers in peer review. We are grateful for their involvement and thoughtful\nconsideration of our work.\nReviewer #5 (Remarks to the Author):\n1. The large plasticity is attributed to the hopping of Ag ions to adjacent vacancies.\nDoes the slight Ag variation of Ag Te have influence on the mechanical properties?\n2+x\nAuthor Reply: We thank you for this insightful question, which gets to the heart of the\nproposed deformation mechanism. You are correct to hypothesize that the stoichiometry,\nspecifically the Ag vacancy concentration in Ag Te, should indeed have a significant\n2+x\ninfluence on the mechanical properties, particularly the plasticity mediated by Ag ions\nhopping. We completely agree with this, and in fact, we have conducted dedicated\nexperiments to directly investigate this effect (as shown in the Figure below).\n1. The initial, linear and elastic stage of all three compositions is virtually identical.\nThis indicates that the slight deviation in Ag content does not significantly alter the\nbond stiffness or the initial elastic modulus of the material.\n2. The primary effect of stoichiometry is observed in the tensile stress behavior. In the\nAg-deficient sample (Ag Te, red curve), we observe the lowest yield stress but\n1.994\nthe largest fracture strain. This is fully consistent with our mechanism: a higher\nintrinsic vacancy concentration provides more pathways for Ag⁺ hopping, allowing\nthe domain rotation process to initiate more easily (lower stress) and sustain\nextensive deformation (higher ductility) before failure. Conversely, in the Ag-rich\nsample (Ag Te, blue curve), the situation is reversed. The highest yield stress is\n2.006\nrequired to initiate plasticity, accompanied by a reduced fracture strain. This\nconfirms that a lower vacancy concentration creates a \"bottleneck\" for ion migration,\nincreasing the stress needed to activate the mechanism. Ultimately, the limited\nnumber of hopping pathways may lead to earlier fracture. The stoichiometric Ag Te\n2\n(black curve) exhibits intermediate behavior, as expected. It demonstrates that the\nAg vacancy concentration is indeed a critical tuning parameter for the plastic\nbehavior. It provides strong support for the \"ionic-hop-mediated domain rotation\"\nmechanism.\nRevised Figure S2: Tensile stress-strain curves for Ag Te (x=-0.006, 0, 0.006).\n2+x\nIn conclusion, we thank you for raising this pertinent point. Our new experimental data\nnot only confirm your hypothesis but also directly validate the core deformation\nmechanism we propose. We have added a discussion of these results in the manuscript,\nstrengthening the link between stoichiometry, vacancy concentration, and mechanical\nperformance. Line 207-209: “The critical role of Ag⁺ migration suggests that the\nstoichiometry, and hence the Ag vacancy concentration, in Ag₂₊ₓTe is expected to be a\nkey factor in modulating its plastic behavior, offering a promising avenue for future\nmaterials engineering.”\n2. What is the direction of the two migration paths of Ag ions in DFT calculations? And\nwhy are these two paths chosen for calculations? Are there specific crystallographic\nplanes or directions that facilitate this hopping more readily than others?\nAuthor Reply: We thank you for these insightful questions regarding the atomic details\nof the Ag ion migration paths. The choice of these paths is central to our proposed\nmechanism, and we are pleased to clarify the rationale behind our DFT calculations.\n1. The two Ag⁺ migration paths (Path 1 and Path 2) shown in Figure 4a were chosen\nbased on the atomic-scale experimental observations. As detailed in the main text\nand illustrated in Figure 3b, the proposed deformation mechanism involves the\nhopping of an Ag ion from a compressed tetrahedron into an adjacent, expanded\ntetrahedral site (which is a pre-existing vacancy in the structure). Path 1 and Path 2\nrepresent the two shortest and most symmetric hopping trajectories between these\nspecific crystallographic sites that are involved in the domain rotation process, as\ndirectly implied by our atomic model in Figure. 3b. To illustrate this, we have\namended the description in lines 196-198 of the revised manuscript as follows: “We\ncalculated the migration barriers for the two most probable paths (Path 1 and Path\n2, Figure. 4a) connecting adjacent tetrahedral sites involved in the domain rotation.”\n2. Our analysis confirms that the transition process exhibits high anisotropy and is\npromoted along specific crystallographic directions and planes. As illustrated below,\nunder tensile stress, the anisotropic deformation of the tellurium sublattice\npreferentially activates Ag⁺ migration along the [5̅1̅ 2] direction. This direction\nintersects the plane where vacancies are concentrated (the (100) plane), thereby\nfacilitating ion migration. These favourable conditions promote collective,\ncooperative hopping along the [5̅1̅2] direction, enabling the tellurium sublattice to\ncoordinate shear and rotation. This ultimately results in the observed reorientation\nof the crystalline domain.\nRevised Figure S3: Schematic of Ag ion hopping and the hopping occurs along the\n[5̅1̅2] direction.\nIn summary, the two calculated paths represent the most crystallographically and\nenergetically favorable local routes identified by our model. Furthermore, these hops\nare integrated into a broader crystallographic system, where the [5̅1̅2] direction being\nparticularly facilitative, as they directly enable the stress-induced, cooperative ion\nmigration responsible for the ionic-hop-mediated domain rotation.\n3. How does the plasticity mechanism respond to different strain rates? Is there a critical\nstrain rate beyond which the Ag⁺ hopping mechanism becomes too slow to\naccommodate the deformation, leading to brittle fracture? Conversely, at very low strain\nrates, does the material exhibit even greater plasticity?\nAuthor Reply: We thank you for this insightful question regarding the strain rate\nsensitivity of our proposed plasticity mechanism. Based on the fundamental nature of\nthe Ag⁺ hopping process and our experimental conditions, we conclude that the ionic-\nhop-mediated domain rotation is highly robust and shows little dependence on strain\nrate within conventional testing regimes.\n1. The core of our mechanism is the stress-induced hopping of Ag⁺ into adjacent\nvacancies. This is an activated process with an extremely short intrinsic timescale.\nThe analysis of mean squared displacement (MSD, revised Supplementary Fig. 9)\nconfirm that the Ag⁺ are highly mobile, with hopping events occurring on the\npicosecond to nanosecond scale. In contrast, the strain rate used in our macroscopic\ntensile tests (0.2 mm/s) translates to an exceptionally slow loading process\ncompared to the ionic hopping rate. The mechanical deformation is thus effectively\na \"quasi-static\" perturbation from the perspective of the fast-moving Ag⁺.\n2. Therefore, in our experiments and under virtually all practically relevant strain rates,\nthe Ag⁺ hopping mechanism is always fast enough to accommodate the deformation\nby facilitating domain rotation. There is no critical strain rate, within the scope of\nstandard mechanical testing, beyond which this mechanism becomes rate-limiting\nand leads to brittle fracture.\n3. Conversely, at very low strain rates, the Ag⁺ have even more redundant time to\nreconfigure, but this does not necessarily translate to \"greater\" plasticity in terms of\nultimate tensile strain. The maximum strain is likely governed by the geometric\nlimits of the domain rotation process and the connectivity of the vacancy network,\nrather than by the kinetics of ion migration. The remarkable plasticity we observe\n(average ~12.13%) is thus a fundamental property of the material under common\ntesting conditions.\nIn summary, the Ag⁺ hopping mechanism is exceptionally rapid and is not the rate-\nlimiting step in the deformation of Ag Te within conventional strain rate regimes. This\n2\ninsensitivity to strain rate is a key advantage, ensuring reliable ductile performance\nacross a wide range of practical loading conditions.\n4. There are a few typos in the manuscript such as “Temsile” in Figure 1b, “Figure 6a”\nin line 137.\nAuthor Reply: We thank you for pointing out these typographical errors. We have\ncarefully checked the entire manuscript and corrected all identified errors, including:\n1. \"Temsile\" in Figure. 1b has been corrected to \"Tensile\".\n2. \"Figure 6a\" has been corrected to \" Supplementary Fig. 8a\" in line 181-182 in\nthe revised manuscript.\n3. Other minor errors such as grammatical mistakes, inconsistent notations, and\nformatting issues have been fixed (e.g., \"Base on\" → \"Based on\", \"Although\nthere are many structural variants, the α-Ag Te sample used in our\n2\nexperiments are determined to have the monoclinic structure... \" →\"Although\nthere are many structural variants, the α-Ag Te sample used in our\n2\nexperiments is determined to have the monoclinic structure...\", \"preparation\nAg Te beams\" →\"preparation of Ag Te beams\").\n2 2\nWe apologize for these oversights and have thoroughly proofread the manuscript to\nensure such errors are eliminated. The changes have been implemented throughout the\ntext and Figures.\nResponses to Reviewers’ comments\nReview: Room-temperature plasticity in Ag Te induced by Ag ions hopping.\n2\n(NCOMMS-25-66818-T)\nBy Anan Guo, Lingxiao Yu, et al.\nDear Reviewers:\nWe express our sincere gratitude to the reviewers for dedicating their time and effort to\ncarefully review our manuscript and provide insightful comments. We truly appreciate\ntheir valuable suggestions. We have revised our manuscript in response to their\nfeedback, and the point-by-point responses to their comments are enclosed.\nReviewer #1 (Remarks to the Author):\nThe authors revised all my opinions and can be published as it is now.\nAuthor Reply: We sincerely thank you for your time, insightful comments, and\nconstructive suggestions throughout the review process. We are also grateful for the\npositive assessment and the recommendation for publication. All points raised have\nbeen addressed in the revised manuscript, and the suggestions have significantly\nstrengthened the quality and clarity of our work.\nReviewer #2 (Remarks to the Author):\nAll the questions have been addressed, and the suggestions have been incorporated\nsatisfactorily. I especially like the in-depth analyses of the rotation domain structures\nand distinguishing them from deformation twins. The manuscript is now in much better\nshape and merits publication.\nAuthor Reply: We thank you for confirming that all issues have been resolved and\nsuggestions fully incorporated. We particularly appreciate your acknowledgement of\nthe in-depth analysis of the rotation domain structure and its distinction from\ndeformation twins. We are grateful for your assessment that the manuscript's quality\nhas been significantly enhanced and is worthy of publication.\nReviewer #3 (Remarks to the Author):\nThe authors answered my questions. I can recommend to publish this manuscript.\nAuthor Reply: We are profoundly grateful for your constructive suggestions and\npositive assessment of the revised manuscript. We thank you for acknowledging that\nour responses adequately address the raised concerns and for recommending\npublication. We extend our sincere appreciation to you for your thorough engagement,\nwhose professional dedication has significantly elevated the scholarly quality of our\nwork.\nReviewer #4 (Remarks to the Author):\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports.\nThis is part of the Nature Communications initiative to facilitate training in peer review\nand to provide appropriate recognition for Early Career Researchers who co-review\nmanuscripts.\nAuthor Reply: We thank you for participating in the Nature Communications Joint\nReview Initiative, which aims to promote peer review training and recognize early-\ncareer researchers.\nReviewer #5 (Remarks to the Author):\nI have read the comments of the reviewers and the authors’ response. I agree with most\nof the technical comments of other reviewers. I think the authors have addressed many\nof these concerns, and may be re-considered for publication after proper revisions.\nParticularly, I think the most important finding of this work is the large tensile\ndeformation of the bulk Ag Te. According to previous studies, Ag Te bulk materials are\n2 2\nbrittle (Adv. Electron. Mater. 2025, 11, 2400728; Natl Sci Open, 2025, Vol.4,\n20250005). Therefore, I suggest providing more convincing results and explanation for\nthe bulk plasticity.\nAuthor Reply: We thank you so much for your positive assessment of our revisions,\nespecially and for highlighting the significance of bulk plasticity in Ag Te. Below, we\n2\nrespond your valuable comments point-by-point, adding new experimental data\naccordingly.\n1. Please provide the photos or SEM images of the bulk samples before and after tension\nto clearly show the elongation as well as possible ductile fracture morphology. In\naddition, please explain the difference in samples preparation, quality or structure\nbetween this ductile Ag Te and previous brittle Ag Te.\n2 2\nAuthor Reply: Many thanks for the advice. We have added photos of the bulk samples\nbefore and after tension (as Supplementary Fig. 2c. Comparing the photos, the width\nhas been reduced from ~2.2 mm to ~2.0 mm, while the length increases from ~15.2 mm\nto ~15.3 mm (after tension). The ductile fracture morphology is clearly different from\nthose driven by dislocations (which shows clearly a gradually-shrunk necking\nphenomenon). What we observed is a nearly uniform elongation. The corresponding\nstrain-stress data of the experiments yields also ~12% ductile deformation (as shown in\nFigure R1), which is consistent with those tested previously. Also, the other\nmacroscopic image of the fractured sample is provided in Supplementary Fig. 6a,\nshowing a nearly uniform elongation (along the stress direction) morphology. Finally,\nthis further confirms the excellent plasticity of bulk Ag Te.\nphotos of the Ag Te beam before and after tensile testing (Supplementary Fig. 2c) show\n2\na nearly uniform elongation due to the ductile deformation. line 153-154: consistent\nwith the observations in both Supplementary Fig. 2c and Supplementary Fig. 4a.\nSupplementary Fig. 2: The tensile stress-strain curve of Ag\nMTS universal testing machine (b) The model diagram of the sample tensile beam. The\nmaximum strain rate is 12.92%, among the experiments. (c) Optical micrographs of the\nspecimen's tensile beam before and after fracture. The post-tensile fracture surface\nexhibits a ductile fracture morphology with no necking. (line 38-40, Revised\nSupporting Information)\nFigure R1: The tensile stress-strain curve of Ag Te for supplementary\nRegarding the differences between our ductile Ag Te and the brittle Ag Te reported in\n2 2\nprevious studies (e.g., Adv. Electron. Mater. 2025; Natl Sci Open 2025), we attribute\nthis to variations of samples (possibly in their microstructure and composition\nvariations, etc.).\n1) Due to different methods and other detailed factors involved in bulk sample\npreparation, they may have different microstructures and composition (and\ncomposition variations, etc.). Our Ag Te sample was synthesized via vacuum\n2\nmelting and annealing (as described in lines 285–290 of the main document),\ninvolving slow cooling and prolonged annealing at 673 K for 3 days to achieve\nhigh-purity monoclinic α-Ag Te (verified by XRD in Supplementary Fig. 1).\nthe reported brittle Ag Te in the cited studies may result from rapid cooling,\n2\nor non-equilibrium methods like mechanical alloying or spark plasma\nsintering (SPS), which can introduce pre-existed and concentrated strain. For\ninstance, the Ag Se Te materials prepared by SPS (National Science Open,\n2 1-x x\n2025) exhibit brittleness due to residual stresses. Among a series of Ag Te\n2 1-\nS materials (Advanced Electronic Materials, 2025), Ag Te was prepared by\nx x 2\nmelting-annealing, with shorter high-temperature melting time and faster\ncooling rate. As such, the prepared Ag Te is brittle.\n2\n2) There are also reports showing that Ag Te-based alloys are ductile. In the work\n2\n(Feng, L. et al. Highly deformable Ag Te Se -based thermoelectric\n2 1-x x\ncompounds. Materials Today Physics 33, 101051 2023), it was demonstrated\nhigh deformability in Ag Te₁₋ₓSeₓ compounds. Also, Wang et al., (Wang, H. et\n2\nal. Synergetic Enhancement of Strength–Ductility and Thermoelectric\nProperties of Ag Te by Domain Boundaries. Advanced Materials 35, 2023)\n2\nhighlights the role of domain boundaries in enhancing plasticity. This\nconsistency may underscore that the sample preparation method optimizes the\nintrinsic ductility in Ag Te.\n2\n2. The tensile strains are nearly the same for the macroscopic (bulk) and the microscopic\n(in-situ STEM) specimens, around 12%. However, the macroscopic strength is smaller\nthan 10 MPa, so how about the strength of the microscopic one? A more detailed\nanalysis on the similarity or difference between the macroscopic and microscopic\nmaterials is needed.\nAuthor Reply: We thank you for highlighting the significant disparity in yield strength\nbetween the macro- and micro-scale Ag Te specimens. We agree that this \"Size Effect\"\n2\nwarrants a deeper explanation. To address this, we conducted supplementary in-situ\nmechanical experiments and provide a detailed multi-scale analysis below.\n1. Following your recommendation, we employed an in-situ TEM mechanical testing\nplatform to perform quantitative tensile tests on micro-specimens (~780 × 326 ×\n205 nm³) machined from the bulk macro-sample (Figure R2a). The resulting stress-\nstrain curves confirm the disparity: the micro-specimens exhibit a yield strength of\n~600 MPa, far exceeding the ~10 MPa observed in macroscopic tests. Crucially,\ndespite this huge strength difference, the micro-specimens exhibited a total tensile\nstrain of ~14% (Figure R2b), which is remarkably similar to the ~12% ductility\nobserved in the macroscopic bulk samples. This similarity in strain limits strongly\nsuggests that the underlying plastic deformation mechanism is intrinsic to the\nmaterial, regardless of scale.\nFigure R2: In-situ tensile test and mechanical response of the Ag Te. (a) Schematic\n2\nand SEM/TEM images of a representative micro-pillar specimen fabricated by FIB for\nin-situ TEM tensile testing. The central lower image shows the SEM image of Ag Te\n2\nbeam viewed from the side, enabling thickness characterization. And the right one\npresents the TEM view (front view), providing information on the tensile beam's length\nand width. (b) TEM images of the Ag Te microcolumn before and after fracture,\n2\ndemonstrating ductile elongation (left). Corresponding in-situ stress-strain curve (right).\nIt reveals a high tensile strength of ~600 MPa and a fracture strain of ~14%, confirming\nthe synergistic coexistence of strength and ductility at the micro-scale.\n2. The strength disparity does not imply different mechanisms; rather, it reflects the\ndifferent energy barriers required to nucleate the \"domain rotation\" mechanism in\nsingle crystals versus polycrystals.\nFirstly, the consistency in plastic strain (~12–14%) across scales confirms a\nshared deformation mode. At the micro-scale, in-situ STEM imaging (Figure 1d)\ncaptures the continuous rotation of individual domains. At the macro-scale, EBSD\nanalysis of fracture surfaces (Figure 2c) reveals widely distributed domains with\nidentical rotation angles (~91.8°). This confirms that \"domain rotation\" is the\nuniversal carrier of plasticity in Ag Te.\npristine surfaces and negligible internal defects (no grain boundaries). To trigger\ndomain rotation, the applied stress must overcome the intrinsic energy barrier to\ndeform the Te sublattice and drive collective Ag ions migration across the entire\ndomain volume simultaneously. This represents \"Homogeneous Nucleation\" of the\nlattice rotation, which requires high stress levels (~600 MPa) approaching the\ntheoretical strength of the lattice.\nThirdly, the macroscopic samples are polycrystalline aggregates containing\nnumerous grain boundaries (GBs) and pores. These defects act as potent stress\nconcentrators. Under a low global applied stress (~10 MPa), the local stress at GBs\ncan reach the threshold required to trigger domain rotation. Once nucleated at these\n\"weak points,\" the rotation propagates through the material. This represents\n\"Heterogeneous Nucleation.\"\nIn summary, the disparity between 10 MPa and 600 MPa is a classic\nmanifestation of the transformation from defect-controlled (macro/polycrystalline)\nto nucleation-controlled (micro/single-crystal). The micro-experiments reveal the\nhigh intrinsic stress required to drive the lattice rotation, while the macro-\nexperiments demonstrate how the material cleverly utilizes grain boundaries to\ntrigger this mechanism at low energy costs, thereby achieving high ductility. This\nconfirms that ion-hopping-mediated domain rotation is the robust, universal\nmechanism underpinning Ag Te's plasticity across all scales.\n2\n3. Does the ductile Ag Te bulk show large bending strain as well?\nductile Ag Te bulk material also exhibits excellent bending strain capacity. To directly\n2\nverify this, we supplemented the study with three-point bending experiments, the\nresults of which unequivocally confirm the material's ductile behavior under large\nbending deformations.\n1. As illustrated in Figure R3, the Ag Te bulk exhibits significant plastic deformation\n2\nduring bending tests. Firstly, the sample maintained a straight bar configuration\nprior to bending. Post-bending, only a non-through crack was observed in the\ncentral region without major deformation, visually demonstrating its exceptional\nductility and fracture resistance. Secondly, the bending stress-strain curve (Figure\nR3b) indicates fracture only occurs at an engineering strain of ~13.1%,\ncorresponding to a peak bending stress of ~149 MPa. This quantitative result aligns\nclosely with the ~12% fracture strain obtained from macroscopic tensile testing,\nconfirming from another dimension (bending mode) that the material possesses a\nlarge strain capacity exceeding 12%.\n2. This high bending strain capacity is intrinsically consistent with the exceptional\ntensile plasticity (~12% tensile strain) reported in our work. This high ductility,\nexhibited under different loading modes (tension, bending), collectively\ndemonstrate the universal deformation capability of Ag Te bulk as an inherently\n2\nductile material, rather than an accidental phenomenon specific to a particular\nloading direction. We propose that this robust ductility under multiaxial loading\nstems from the core plasticity mechanism we have uncovered: stress-driven ion\nhopping-mediated domain rotation. Under the complex stress field of bending\nloading (compression on one side, tension on the other), this mechanism similarly\nadapts to strain through coordinated rotation of lattice domains, thereby preventing\ncrack initiation and propagation and enabling uniform large deformation.\nIn summary, combining direct bending experimental evidence with tensile plasticity\ndata, we can unequivocally conclude that the ductile Ag Te bulk material prepared in\n2\nthis study exhibits not only outstanding tensile ductility but also exceptional large\nbending strain capacity. This further supports its immense potential as a durable\nelectrode or functional component for next-generation flexible/wearable thermoelectric\ndevices.\nFigure R3: Mechanical performance of bulk Ag Te in three-point bending tests. (a)\nengineering stress-strain curve. Material fracture occurred at ~13.1% engineering strain,\ncorresponding to a peak bending stress of ~ 149 MPa. This strain value aligns closely\nwith macroscopic tensile test results (~12%), confirming Ag Te's capacity to\n2\naccommodate large strains under bending modes."}]

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