# Double and double double perovskites in the RMnMnTaO6 series

K. Ji, Y. Yuan, G.T. Moyo, C. Ritter, J.P. Attfield

► To cite this version:

K. Ji, Y. Yuan, G.T. Moyo, C. Ritter, J.P. Attfield. Double and double double perovskites in the RMn-MnTaO6 series. Journal of Solid State Chemistry, 2022, 313, pp.123329. 10.1016/j.jssc.2022.123329. hal-05442042

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# Double and double double perovskites in the RMnMnTaO₆ series

K. Ji<sup>a</sup>, Y. Yuan<sup>a</sup>, G.T. Moyo<sup>a</sup>, C. Ritter<sup>b</sup>, J.P. Attfield<sup>a,*</sup>

<figure><img src="image_2.png" /></figure>

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## ABSTRACT

A new family of perovskites RMnMnTaO₆ has been synthesised at high pressure for representative R = La, Nd, Sm, Eu, Gd, Y and Lu that span the whole rare earth series. The structure type changes from tetragonal P4₂/n double double perovskite (DDPv) type with columnar R³⁺/Mn²⁺ cation order (R = La, Nd, Sm) to monoclinic P2₁/n double perovskite (DPv) (R₀.₅Mn₀.₅)₂MnTaO₆ (R = Sm, Gd, Y, Lu) as R³⁺ cation size decreases. No antisite disorder or nonstoichiometry is observed. Spin ordering transitions are observed below 70 K and a neutron diffraction study of DDPv NdMnMnTaO₆ reveals ferrimagnetic orders at Tc₁ = 65 K and Tc₂ = 40 K with Mn-spin reorientation due to Nd moment order at Tc₂ leading to magnetoelastic coupling.

## 1. Introduction

Perovskite oxides ABO₃ have many notable physical and chemical properties due to their versatile structures in accepting a large variety of cations on A- and B-sites [1–5]. Their compositions can be modified to induce (100) layered, (110) columnar, or (111) rock-salt 1:1 cation ordering arrangements [6], leading to AA'·B₂O₆ [7] or A₂BB'·O₆ [8] double perovskites (DPv). Many layered AA'·B₂O₆ and rock-salt A₂BB'·O₆ DPv's (Fig. 1b) have been reported and the orders enable novel physical properties such as ferrimagnetism and half-metallicity in Sr₂FeMoO₆ [9] with large magnetoresistance at room temperature. High pressure synthesis can be used to stabilise ordering of cations on both perovskite sublattices to generate more complex structures. This was exploited to generate 1:2 ordered families RSr₂MCu₂O₉,y (R = rare earth, M = transition metal) of layered copper oxides with oxygen vacancy ordering (y ≈ 1) for studies of superconductivity [10]. More recently, 1:1 ordered double double (double-ordered) perovskites (DDPv) that are oxygen stoichiometric (i.e. AA'·BB'·O₆) have been explored. Materials with layered A-site and rock-salt B-site ordering are favoured by A⁺/A³⁺ charge difference e.g. Na⁺/R³⁺ [11,12]. A second DDPv type combining columnar A-site and rock-salt B-site orders, stabilised by A/A' cation size difference, has been observed for RMnMnSbO₆ [13,14] and several CaMnBB'·O₆ materials (B = Mn, Fe, Co, Ni and B' = Re [15–17]; B/B' = Cr/Sb and Fe/Sb [18], Fe/Ta [19], and Mn/W) [20] have been synthesised at high pressure.

R³⁺ cation size is well-known as a tuning effect on perovskite properties, and more subtle electronic effects on synthesis conditions have also been reported [10]. Within the RMnMnSbO₆ series, R³⁺ size was found to lead to a dramatic switch in cation ordering, from double double (DDPv) AA'·BB'·O₆ order for larger R = La, Pr, Nd, Sm to a double

perovskite (DPv) (A₀.₅A'₀.₅)₂BB'·O₆ structure where A/A' cations are statistically disordered for smaller R = Eu, Gd [13]. The two structure types are shown in Fig. 1. To discover whether the same structural change can be observed in other families, we have explored the new RMnMnTaO₆ series across the full R = La–Lu, Y range, and detailed results are reported in this paper. Both DDPv and DPv polymorphs of the R = Sm member (and CaMnMnTaO₆) were discovered as a function of synthesis temperature at pressure, as reported elsewhere [20].

## 2. Experimental details

RMnMnTaO₆ compositions for representative R = La, Nd, Sm, Eu, Gd, Y and Lu were treated under high pressure-temperature conditions using a Walker-type multi anvil apparatus. Stoichiometric ratios of RTaO₄ and MnO were packed in a Pt capsule, compressed to 10 GPa pressure and heated at temperatures from 1200 to 1650 °C for 30 min. Temperature was quenched followed by slow pressure release to ambient. RTaO₄ precursors were obtained by standard solid-state reaction; a pellet of preheated R₂O₃ and Ta₂O₅ was heated at 1623 K for 24 h with intermediate regrinding and repelleting.

The polycrystalline products were characterised by powder X-ray diffraction (XRD) using a Bruker D2 instrument employing Cu Kα radiation. Neutron powder diffraction (NPD) data were collected for the DDPv NdMnMnTaO₆ sample on beamline D20 at the ILL facility; with wavelength λ = 1.54 Å at 300 K for refinement of the crystal structure; and with λ = 2.41 Å at 1.7, 50 and 80 K for studying magnetic ordering. Short scans with λ = 2.41 Å from 1.5 to 80 K in 1 K intervals were also recorded to follow the temperature dependence of multiple spin ordering and potential spin reorientation transitions.

<footnote><sup>a</sup> Centre for Science at Extreme Conditions (CSEC) and School of Chemistry, The University of Edinburgh, EH9 3FD, UK</footnote>

<footnote><sup>b</sup> Institut Laue-Langevin, 38042, Grenoble, Cedex, France</footnote>

<footnote>* Corresponding author.
E-mail address: j.p.attfield@ed.ac.uk (J.P. Attfield).</footnote>
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** (a) Tetragonal P42/n double double perovskite (DDPv), and (b) monoclinic P21/n double perovskite (DPv) RMnMnTaO6 crystal structures. A-site Mn/R cations are disordered in the DPv structure but have a columnar ordering in the DDPv with the A-column Mn cations having alternating tetrahedral (MnAT, dark grey sphere) and square-planar (MnAS, light grey sphere) coordination environments as shown to the left. R3+ cations are shown as large grey spheres. Mn2+ and Ta5+ are in octahedral coordination with rock-salt type ordering in both structures.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Powder X-ray diffraction (XRD) patterns of RMnMnTaO6 samples synthesised at 1200 °C under 10 GPa pressure. A-site ordering in the DDPv samples is evidenced by the arrowed (110) peak (R = La, Nd, Sm) and is absent for DPv materials (R = Eu, Gd, Y, Lu). RTaO4 secondary phases are present in all samples, with increasing amounts for small R = Y and Lu, and the most intense peak is marked by a star on the R = Eu profile. Rietveld fits to these data are shown in the SI.</figcaption></figure>

Magnetisations were measured on a Quantum Design MPMS SQUID magnetometer. Magnetic susceptibilities were recorded using zero-field cooled (ZFC) and field cooled (FC) conditions for an external field of 0.1 T. Isothermal magnetisation measurements at several temperatures were undertaken using fields from -5 to 5 T.

# 3. Results and discussion

## 3.1. Phase formation and XRD

Seven RMnMnTaO6 compositions were investigated (R = La, Nd, Sm, Eu, Gd, Y and Lu). Laboratory X-ray diffraction patterns (Fig. 2) showed that R = La and Nd formed the DDPv double double perovskite phase at all temperatures, as a characteristic peak for columnar A-site R/Mn

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Refined lattice parameters and cell volume plotted against the R3+ ionic radius for RMnMnTaO6 samples, with R shown at the top. The broken vertical line shows the boundary between tetragonal P42/n DDPv's and monoclinic P21/n DPv's. *a* and *b* lattice parameters for the latter are scaled by √2 for comparison. Error bars are smaller than the data points.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Phase diagram for the RMnMnTaO6 series as a function of synthesis temperature and R3+ ionic radius with R shown at the top. Double perovskite (DPv) and double double perovskite (DDPv) domains are indicated, with a narrow intermediate region of DPv/DDPv coexistence for R = Sm [20].</figcaption></figure>

cation ordering was observed near 2θ = 16°. Smaller R3+ cations from Eu to Lu formed the double perovskite DPv phase without A-site R/Mn ordering. R = Sm shows a crossover from DDPv to DPv structures with increasing synthesis temperature as reported elsewhere [20]. Rietveld fits to the diffraction patterns (Fig. S1) revealed small amounts of RTaO4 and Mn3O4 secondary phases. The fits confirmed that the DDPv phases have the tetragonal P42/n structure found previously for analogous materials, while the DPv's have the commonly found monoclinic P21/n structure. Lattice parameters and cell volumes in Fig. 3 show systematic changes consistent with increasing R3+ ionic radius. Detailed crystallographic information is summarised in Tables S1–S3. A phase diagram displaying synthesis results at 10 GPa is shown in Fig. 4.

## 3.2. Magnetisation

Magnetisation measurements were performed for each sample except R = Lu as this contained a relatively large amount of secondary phases. Representative data for the R = Nd DDPv and the R = Gd DPv phases are shown in Fig. 5 and data for other R are in SI. Extracted magnetic parameters are shown in Table 1. High-temperature susceptibilities for all samples follow the Curie-Weiss equation except for R = Eu where a temperature-dependent moment is evident and the data do not follow Curie-Weiss behaviour. Fitted effective paramagnetic moments in Table 1
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Magnetisation plots for representative RMnMnTaO₆ samples; (a) and (b), DDPv R = Nd, and (c) and (d), DPv R = Gd. (a) and (c) show ZFC and FC susceptibilities and inverse ZFC susceptibilities with a Curie-Weiss fit to high temperature points. (b) and (d) show magnetisation-field data collected at several temperatures.</figcaption></figure>

**Table 1**

Magnetic parameters for RMnMnTaO₆ samples with DDPv or DPv structures. Curie temperatures ($T_C$), theoretical ($\mu_{th}$) and experimental ($\mu_{exp}$) effective paramagnetic moments, and Weiss constants ($\theta$) are from susceptibility data. Saturation ($M_S$) and remnant ($M_R$) magnetisations and coercive field ($B_C$) values are from magnetisation-field loops at 5 K, with values at other temperatures also shown for some samples. Curie-Weiss fitting was not performed for R = Eu as the moment varies with temperature. Values for DDPv and DPv polymorphs of R = Sm were reported in ref. 20 and are shown here for comparison.

<table><thead><tr><th>R</th><th>T<sub>C1</sub>(K)</th><th>T<sub>C2</sub>(K)</th><th>μ<sub>th</sub> (μ<sub>B</sub>)</th><th>μ<sub>exp</sub> (μ<sub>B</sub>)</th><th>θ (K)</th><th>M<sub>S</sub> (μ<sub>B</sub>)</th><th>M<sub>R</sub> (μ<sub>B</sub>)</th><th>B<sub>C</sub> (T)</th></tr></thead><tbody><tr><td>DDPv La</td><td>49</td><td>-</td><td>8.4</td><td>9.1</td><td>-176</td><td>0.19</td><td>0.14</td><td>0.06</td></tr><tr><td>Nd</td><td>65</td><td>40</td><td>9.2</td><td>9.6</td><td>-141</td><td>0.93</td><td>0.88</td><td>0.07</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>0.24<sup>a</sup></td><td>0.25<sup>a</sup></td><td>0.18</td></tr><tr><td>Sm</td><td>69</td><td>18</td><td>8.5</td><td>9.4</td><td>-217</td><td>0.01</td><td>0.02</td><td>0.04</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>0.05<sup>b</sup></td><td>0.04<sup>b</sup></td><td>0.17</td></tr><tr><td>DPv Sm</td><td>35</td><td>-</td><td>8.5</td><td>8.9</td><td>-156</td><td>0.03</td><td>0.06</td><td>0.08</td></tr><tr><td>Eu</td><td>26</td><td>13</td><td>9.1</td><td>-</td><td>-</td><td>0.73</td><td>0.30</td><td>0.03</td></tr><tr><td>Gd</td><td>45</td><td>20</td><td>11.5</td><td>11.46</td><td>-60</td><td>6.19</td><td>0</td><td>0</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>2.87</td><td>0</td><td>0</td></tr><tr><td>Y</td><td>28</td><td>-</td><td>8.4</td><td>13.4</td><td>-390</td><td>0.20</td><td>0.10</td><td>0.11</td></tr></tbody></table>

are near to the theoretical composite values for spin-only S = 5/2 Mn²⁺ and R³⁺ cations in their ground J-states, except for R = Y which is attributed to the sample containing a significant amount of secondary phases. Negative Weiss temperatures evidence dominant antiferromagnetic interactions between spins.

All samples show a ferro- or ferri-magnetic ordering at a transition $T_{C1}$ between 26 and 69 K, and some materials containing magnetic R³⁺ cations show a second transition at $T_{C2} = 13–40$ K, suggesting respective ordering of the Mn²⁺ and R³⁺ moments at the two transitions.

Divergence of ZFC and FC susceptibilities is observed at low temperatures and M-H loops show corresponding hysteresis loops below $T_{C1}$ with small coercive fields (<0.11 T) at 5 K. Saturated magnetisations at 5 K extrapolated to zero field are small (<0.2 μ<sub>B</sub>) for R = La, Sm and Y samples, suggesting that the likely spin order is ferrimagnetic with antiparallel coupling of inequivalent Mn²⁺ moments at A and B sites. R = Nd, Eu and Gd samples have larger saturated moments at 5 K, in particular a value of 6.2 μ<sub>B</sub> for R = Gd, showing that Mn²⁺ and R³⁺ moments are involved in the ferrimagnetic order.

<footnote>a Measured at 50 K.</footnote>

<footnote>b Measured at 30 K.</footnote>
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Low angle neutron diffraction data (λ = 2.41 Å) for NdMnMnTaO₆. (a) Comparison of long scans at several temperatures showing starred magnetic contributions appearing below the spin ordering transitions at T<sub>C1</sub> = 65 K and T<sub>C2</sub> = 40 K. (b) Short-scan thermodiffraction neutron intensities showing magnetic contributions at low temperatures, with the expansion in (c) revealing redistribution of magnetic intensity from the (200) to the (002) peak on cooling through T<sub>C2</sub> that evidences spin reorientation.</figcaption></figure>

### 3.3. Neutron powder diffraction study of NdMnMnTaO₆

NdMnMnTaO₆ was chosen as a representative DDPv for NPD study to obtain accurate oxygen positions and to determine the low-temperature spin structures. Rietveld fits to high resolution data collected at 300 K showed that all crystallographic sites were fully occupied and no antisite cation disorder was observed. This reflects the large cation size difference between Nd³⁺ (1.29 Å) and Mn²⁺ (0.96 Å) at A-sites, as well as a large charge difference between Mn²⁺ and Ta⁵⁺ at B-sites. Full results are shown in SI.

On cooling below T<sub>C1</sub> = 65 K, magnetic intensities appear on nuclear peaks such as (110), (111), (200) (Fig. 6a) and are indexed by the [000]

<figure><img src="image_9.png" /><figcaption>**Fig. 8.** Temperature evolution of refined lattice parameters and cell volume for tetragonal DDPv NdMnMnTaO₆ from Rietveld fits to short NPD scans.</figcaption></figure>

propagation vector. Magnetic intensities at 50 K data are fitted well by a simple ferrimagnetic model ($R_{mag}$ = 2.43%) in which A- and B-site Mn²⁺ spins are antiparallel and aligned along the c-direction (Fig. 7a), without Nd³⁺ moments being ordered at this temperature. A and B site Mn spins were constrained to have the same magnitude in the refinements, although magnetisation data show that they differ slightly, by 0.24 µB at 50 K (Table 1). Dominant antiferromagnetic coupling between ferromagnetic A and B sublattice spins is consistent with the negative Weiss temperature. Further cooling below T<sub>C2</sub> = 40 K leads to changes in magnetic intensity distribution, as shown in Fig. 6b and c where the magnetic contribution to (200) decreases while the contribution to (002) increases. This evidences a spin reorientation transition and the magnetic NPD data at 1.7 K are fitted well ($R_{mag}$ = 1.96%) by the model shown in Fig. 7b. The Mn²⁺ spins reorient from being parallel to the c-axis to being perpendicular on cooling through T<sub>C2</sub>, with an ordered moment of 4.5(1) µB at 1.7 K close to the ideal spin-only value of 5 µB. Nd³⁺ moments are ordered ferromagnetically in the ab-plane below T<sub>C2</sub> with a magnitude of 1.2(1) µB at 1.7 K indicating a $J_{eff}$ = ½ ground state due to crystal electric field (CEF) effects that lead to significant anisotropy. Single-ion anisotropy from the Nd³⁺ moments likely drives the reorientation of the Mn²⁺

<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Ferrimagnetically ordered structures of DDPv NdMnMnTaO₆ at (a) 50 K and (b) 2 K with the c-axis vertical. Long/short arrows represent Mn/Nd moments. Up Mn-A and down Mn-B spin sublattices are ordered parallel to the c-axis at 50 K, but reorient perpendicular to this direction with down Nd, up Mn-A, and down Mn-B spin directions at 2 K. Dark and light grey arrows represent moments on Mn<sub>AT</sub> and Mn<sub>AS</sub> sites, respectively.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Fig. 9.** Thermal evolution of tetragonal strain and ordered Mn²⁺ and Nd³⁺ magnetic moments for DDPv NdMnMnTaO₆ from Rietveld fits to short NPD scans. A linear fit to the excess strain below 37 K and critical fits to the moments in the range *T*<sub>C</sub>/2 *<i>t*<sub>C</sub>*</i> are shown, as described in the text.</figcaption></figure>

spins at *T*<sub>C2</sub>. A similar spin rotation transition was observed in the NdMnMnSbO<sub>6</sub> analogue [13]. Rietveld fits to the NPD data are shown in Fig. S3 (ESI).

Fits to the variable temperature NPD data collected between 1.7 and 80 K for NdMnMnTaO₆ were used to extract the lattice parameters and volume shown in Fig. 8. Volume increases smoothly across this range but the lattice parameters show a clear anomaly at *T*<sub>C2</sub> with negative expansion of *a* below 40 K. Comparison of the thermal evolution of the tetragonal strain *e* = (c/*a*) − 1 to the ordered moment variations in Fig. 9 shows that a negative excess strain develops through magnetoelastic coupling below *T*<sub>C2</sub>. Although lattice parameters and volume evolve smoothly through *T*<sub>C2</sub>, the tetragonal strain shows a discontinuity indicating that the transition is first order. This is expected as the magnetic structures above and below *T*<sub>C2</sub> have different irreducible symmetry representations (Γ₁ and Γ₃ respectively [14]) and so the transition between them cannot be continuous.

Magnetoelastic coupling between strain *e* and magnetisation *M* typically has a linear-quadratic dependence, proportional to *eM*² [21]. This is verified by the fit of a critical function *m* = *m*₀[1 − (T/*T*<sub>C</sub>)]*β* where *m* is the ordered Nd³⁺ moment to data below *T*<sub>C2</sub> = 40 K with exponent *β* = 0.5, in keeping with mean field theory, as shown on Fig. 9, while excess tetragonal strain shows a linear (i.e. *β* = 1) dependence over a wide temperature range below 37 K. The interval between 37 and *T*<sub>C2</sub> = 40 K may correspond to a two phase region at the first order transition although this is not resolved in the magnetic fits. A fit of the critical function to the Mn²⁺ moment variation approaching the higher temperature magnetic transition gives *T*<sub>C1</sub> = 64.4(2) K with critical exponent *β* = 0.36(1), in excellent agreement with the theoretical value of *β* = 0.365 for a 3D-Heisenberg magnet. Hence the spin order at *T*<sub>C1</sub> may be viewed as a purely magnetic transition while the combined Mn²⁺ moment reorientation and Nd³⁺ moment order at *T*<sub>C2</sub> is a magnetostructural transition with significant coupling of spins to the lattice through single-ion anisotropy of Nd³⁺.

## 4. Conclusions

In conclusion, cation-ordered perovskites RMnMnTaO₆ are found to exist at 10 GPa pressure across the whole rare earth series. The structure type changes from tetragonal *P*4̅<sub>2</sub>/<n> double double perovskite (DDPv) type with columnar R³⁺/Mn²⁺ cation order (R = La, Nd, Sm) to

monoclinic *P*2₁/*n* double perovskite (DPv) (R₀.₅Mn₀.₅)₂MnTaO₆ (R = Sm, Gd, Y, Lu) as R³⁺ cation size decreases. A similar trend was found for in the RMnMnSbO₆ series. Both structure types are observed for R = Sm but not for other R. Low temperature magnetic transitions are observed and a detailed neutron diffraction study of DDPv reveals ferrimagnetic orders at *T*<sub>C1</sub> = 65 K and *T*<sub>C2</sub> = 40 K with Mn-spin reorientation due to Nd moment order leading to magnetoelastic coupling below *T*<sub>C2</sub>.

### CRediT authorship contribution statement

**K. Ji:** Conceptualization, Formal analysis, Investigation, Writing – original draft, Writing – review & editing. **Y. Yuan:** Investigation, Writing – review & editing. **G.T. Moyo:** Formal analysis, Investigation, Writing – review & editing. **C. Ritter:** Formal analysis, Investigation, Writing – review & editing. **J.P. Attfield:** Conceptualization, Writing – original draft, Writing – review & editing, Supervision, Project administration, Funding acquisition.

### Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Paul Attfield reports financial support was provided by Engineering and Physical Sciences Research Council.

### Acknowledgment

We acknowledge EPSRC for financial support and STFC for the provision of the beamtime at the Institut Laue-Langevin.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jssc.2022.123329.

## References

[1] J.P. Attfield, P. Lightfoot, R.E. Morris, Perovskites, Dalton Trans. 44 (2015) 10541–10542.

[2] C.J. Howard, H.T. Stokes, Group-theoretical analysis of octahedral tilting in perovskites, Acta Crystallogr. Sect. B Struct. Sci. 54 (1998) 782–789.

[3] C.J. Howard, B.J. Kennedy, P.M. Woodward, Ordered double perovskites–a group-theoretical analysis, Acta Crystallogr. Sect. B Struct. Sci. 59 (2003) 463–471.

[4] M.T. Anderson, K.B. Greenwood, G.A. Taylor, K.R. Poeppelmeier, B-cation arrangements in double perovskites, Prog. Solid State Chem. 22 (1993) 197–233.

[5] R.H. Mitchell, Perovskites: Modern and Ancient, Almaz Press, Thunder Bay, 2002.

[6] G. King, P.M. Woodward, Cation ordering in perovskites, J. Mater. Chem. 20 (2010) 5785–5796.

[7] A. Aimi, D. Mori, K.-i. Hiraki, T. Takahashi, Y.J. Shan, Y. Shirako, J. Zhou, Y. Inaguma, High-pressure synthesis of A-site ordered double perovskite CaMnTi₂O₆ and ferroelectricity driven by coupling of A-site ordering and the second-order Jahn–Teller effect, Chem. Mater. 26 (2014) 2601–2608.

[8] S. Vasala, M. Karppinen, A₂BBO₆ perovskites: a review, Prog. Solid State Chem. 43 (2015) 1–36.

[9] K.-I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, Y. Tokura, Room-temperature magnetoresistance in an oxide material with an ordered double-perovskite structure, Nat. 395 (1998) 677–680.

[10] M.Á. Alario-Franco, R. Ruiz-Bustos, A. Dos Santos-García, Ahead of the lanthanide contraction; Pressure and ionic size in the synthesis of MSr₂RECu₂O₈ (RE= rare earth, M= Ru, Cr, Ir): a Gaussian relation, Inorg. Chem. 47 (2008) 6475–6481.

[11] S. García-Martín, E. Urones-Garrote, M.C. Knapp, G. King, P.M. Woodward, Transmission electron microscopy studies of NaLaMgWO₆: spontaneous formation of compositionally modulated stripes, J. Am. Chem. Soc. 130 (2008) 15028–15037.

[12] R. Shankar PN, F. Orlandi, P. Manuel, W. Zhang, P.S. Halasyamani, A. Sundaresan, A-site and B-site cation ordering induces polar and multiferroic behavior in the perovskite NaLnNiWO₆ (Ln= Y, Dy, Ho, and Yb), Chem. Mater. 32 (2020) 5641–5649.

[13] E. Solana-Madruga, Á.M. Arévalo-López, A.J. Dos Santos-García, E. Urones-Garrote, D. Ávila-Brande, R. Sáez-Puche, J.P. Attfield, Double double cation order in the high-pressure perovskites MnRMnSbO₆, Angew. Chem. Int. Ed. 55 (2016) 9340–9344.

[14] E. Solana-Madruga, Á.M. Arévalo-López, A.J. Dos Santos-García, C. Ritter, C. Cascales, R. Sáez-Puche, J.P. Attfield, Anisotropic magnetic structures of the MnRMnSbO₆ high-pressure doubly ordered perovskites (R= La, Pr, and Nd), Phys. Rev. B 97 (2018), 134408.
[15] G.M. McNally, Á.M. Arévalo-López, P. Kearins, F. Orlandi, P. Manuel, J.P. Attfield, Complex ferrimagnetism and magnetoresistance switching in Ca-based double double and triple double perovskites, Chem. Mater. 29 (2017) 8870–8874.

[16] G.M. McNally, Á.M. Arévalo-López, F. Guillou, P. Manuel, J.P. Attfield, Evolution of cation and spin orders in the double-double-double perovskite series CaₓMn₂₋ₓFeReO₆, Phys. Rev. Mater. 4 (2020), 064408.

[17] E. Solana-Madruga, Y. Sun, Á.M. Arévalo-López, J.P. Attfield, Ferri-and ferro-magnetism in CaMnMReO₆ double double perovskites of late transition metals M=Co and Ni, Chem. Commun. 55 (2019) 2605–2608.

[18] E. Solana-Madruga, P.S. Kearins, K.N. Alharbi, C.T. Lennon, C. Ritter, J.P. Attfield, Ferrimagnetism and spin reorientation in the high-pressure double double perovskites CaMnCrSbO₆ and CaMnFeSO₆, Phys. Rev. Mater. 5 (2021), 054412.

[19] P. Kearins, E. Solana-Madruga, K. Ji, C. Ritter, J.P. Attfield, Cluster spin glass formation in the double double perovskite CaMnFeTaO₆, J. Phys. Chem. C 125 (2021) 9550–9555.

[20] K. Ji, K.N. Alharbi, E. Solana-Madruga, G.T. Moyo, C. Ritter, J.P. Attfield, Double double to double perovskite transformations in quaternary manganese oxides, Angew. Chem. Int. Ed. 60 (2021) 22248–22252.

[21] M.A. Carpenter, Static and dynamic strain coupling behaviour of ferroic and multiferroic perovskites from resonant ultrasound spectroscopy, J. Phys. Condens. Matter 27 (2015), 263201.