DOI: 10.5061/dryad.bzkh189qs
title: Data from: Ultra-low thermal conductivity and promising thermoelectric performance in the structurally complex Zintl phase: Eu<sub>14</sub>GaAs<sub>11</sub>

description: Intermetallic Zintl compounds of the Ca14AlSb11 (14-1-11) structure type
 are important for their small bandgap semiconducting behavior and
 exceptionally low thermal conductivity. A new member of this structure
 type, Eu14GaAs11, containing zero-dimensional tetrahedral [GaAs4]9-
 anions, has been synthesized. This compound crystallizes in the tetragonal
 I41/acd space group, similar to other 14-1-11 compounds. Eu14GaAs11 is a
 semiconductor with a bandgap of 0.61 eV, as calculated using the
 Goldsmid-Sharp formula. Electronic transport measurements indicate a high
 Seebeck coefficient of 232 µV/K at 321 K, peaking at 424 µV/K at 713 K.
 The electrical resistivity is particularly high due to low carrier
 concentrations. However, the compound's notable strengths include its
 stability at high temperatures and its ultra-low thermal conductivity of
 0.59 W m⁻¹ K⁻¹ at room temperature, with minimal electronic contribution,
 making it even lower than that of other high-performing Zintl phases.
 Given its low thermal conductivity and high Seebeck coefficient,
 Eu14GaAs11 presents potential for further optimization by adjusting the
 carrier concentration to enhance its thermoelectric performance.
description: Polycrystalline Eu14GaAs11 was synthesized through high-energy
 ball milling and high-temperature solid-state reactions. All procedures
 were conducted in an inert atmosphere glove box. High-purity elemental
 sources, such as Eu ingot (Stanford Advanced Materials, 99.99%), As chips
 (Johnson Matthey Chemicals, 99.9999%), and Ga (Alfa Aesar, 99.99999%),
 were used for synthesis. Binary precursors, EuAs and GaAs, were prepared
 by precisely weighing the necessary stoichiometric amounts of elements
 with a precision balance and milling them in a 65-cm³ stainless-steel
 grinding vial with two stainless steel balls of 12.7 mm diameter, using a
 SPEX 8000D Mixer/Mill for 30 minutes. To ensure homogeneous mixing, the
 mixture was scraped with a chisel and milled again for an hour. The
 homogeneous powder was then sealed in a Ta tube and enclosed within an
 evacuated quartz tube. EuAs was synthesized by annealing at 850 °C for 12
 hours, and GaAs at 650 °C for 12 hours. Eu14GaAs11 was prepared from the
 binary precursors and elements in stoichiometric ratios, following the
 same procedures but annealing at 1100 °C for 96 hours.
 The powder was pressed into pellets using a Dr. Sinter Junior
 Spark Plasma Sintering system (Fuji Electronic Industrial Co., Ltd.) under
 argon gas. The applied force increased from 5 kN to 9 kN, and the pellets
 were sintered at 900 °C for 30 minutes. The density of the pellets
 exceeded 98%, as determined by Archimedes' principle.
 Caution: Arsenic-containing phases may produce toxic arsine gas
 during reactions. The quartz tube was handled in a fume hood, while the
 metal tubes were managed inside the glove box. Proper personal protective
 equipment was worn at all times. Phase characterization
 involved using a Bruker D8 ECO ADVANCE powder X-ray diffraction (PXRD)
 diffractometer on zero-background off-axis quartz plates, with Cu Kα
 radiation, over 2θ angles of 20°−80° with a step size of 0.02°. A portion
 of the densified pellet was mounted on an epoxy resin disk and polished
 with 1000-grit sandpaper, then further polished with a wheel and 1 μm
 colloidal diamond suspension. Scanning electron microscopy (SEM) and
 energy-dispersive X-ray spectroscopy (EDS) were performed using a Thermo
 Fisher Quattro ESEM with a Bruker Quantax EDX detector at 20 kV to analyze
 phase homogeneity and elemental distribution. The EDS composition averages
 data from ten points across the pellet.
 Thermogravimetry and differential scanning calorimetry (TG/DSC)
 analyses assessed thermal stability, conducted from room temperature to
 900 °C under an argon flow of 50 mL/min, with a heating rate of 10
 K/min. Transport properties were measured by
 determining thermal diffusivity with a Netzsch LFA 475 Microflash under
 argon flow, with pellet surfaces coated with graphite to improve laser
 absorption. Total thermal conductivity was calculated via D × Cp × r,
 where D is thermal diffusivity, r is density, and Cp, approximated using
 the Dulong-Petit law, is heat capacity. The Seebeck
 coefficient was measured with a custom instrument under controlled low
 pressure (300 Torr) in a nitrogen atmosphere over 300 K to 775 K.
 Electrical resistivity and Hall measurements used an in-house setup based
 on the van der Pauw method. Hall coefficient measurements employed
 currents of 15-20 mA and a magnetic field of 1 T.
description: # Data from: Ultra-low thermal conductivity and promising thermoelectric
 performance in the structurally complex Zintl phase: Eu~14~GaAs~11~
 Dataset DOI:
 [10.5061/dryad.bzkh189qs](https://doi.org/10.5061/dryad.bzkh189qs) ##
 Description of the data and file structure ### Files and variables ####
 File: Eu14GaAs11_Data.xlsx **Description:** All the data provided in the
 paper. Polycrystalline Eu₁₄GaAs₁₁ was synthesized from high-purity
 elements via high-energy ball milling and solid-state reactions under
 inert atmosphere. Binary precursors (EuAs, GaAs) were prepared, annealed,
 and reacted at 1100 °C to form the final compound, which was densified by
 spark plasma sintering (&gt;98% density). Phase purity and microstructure
 were characterized by PXRD, SEM, and EDS, while thermal and transport
 properties were measured using TG/DSC, LFA, Seebeck, and van der Pauw
 techniques. ##### Variables: The file contains all of the data, from left
 to right: * Powder X-ray diffraction (PXRD) in columns of 2-theta (˚),
 intensity (arbitrary units) - Resistivity vs Temperature (T) in columns of
 T (K) and resistivity (mOhm-cm) * Thermal conductivity vs Temperature (T)
 in columns of T(K) and thermal conductivity (W/mK) - Carrier Concentration
 vs Temperature (T) in columns of T(K) and carrier concentration (cm^-3) *
 Mobility vs Temperature (T) in columns of T(K) and mobility (cm^2 / V*s) -
 Differential scanning calorimetry (DSC), thermal gravimetric (TG) analysis
 vs Temperature (K) in columns of T(K), DSC (mW/mg), TG (Mass/%)