Data from: Diffuson-driven lattice thermal conductivity in Zintl arsenides: disrupting mass-thermal conductivity relation for high thermoelectric performance
Abstract
Zintl compounds of the Ca14AlSb11 structure type, especially Yb14MSb11 (M = Mg, Mn, Zn), have emerged as leading contenders for high-temperature thermoelectric applications because of their very low thermal conductivity and excellent electronic properties. In comparison, the lighter arsenic-based compounds have received less attention, as they are generally thought to have poor thermoelectric performance due to higher thermal conductivity. In this study, we synthesized 4 compounds, Eu14MAs11 (M = Mg, Zn, Cd) and Eu14Zn1.2As11, and refined their powder diffraction patterns using Rietveld refinement. We measured the transport properties of these compounds to demonstrate that diffuson conduction is common across these compositions, resulting in a lattice thermal conductivity of about 0.55 W m-1 K-1 at 298 K and challenging the usual relationship between mass and lattice thermal conductivity. The combination of low thermal conductivity and high valley degeneracy enables these materials to reach impressive thermoelectric performance, with Eu14MgAs11 achieving a maximum zT of 1.3 at 1250 K.
Dataset DOI: 10.5061/dryad.37pvmcvzv
Description of the data and file structure
Four compounds were synthesized and characterized: Eu14MgAs11, Eu14CdAs11, Eu14Zn1.2As11, Eu14ZnAs11.
Synthesis: The compounds were synthesized with binary phases, EuA and M2As3 (M = Mg, Cd, Zn). For the Eu14MgAs11 phase, EuH2 was also employed to achieve phase pure product. Stoichiometric mixtures were milled in a 650 cm3 steel grinding vial with two 12.7 mm balls employing a SPEX mixer-mill. The resulting powder was transferred to a tantalum tube and sealed using an Ar-fille arc welder. The tantalum tube was further sealed in a fused silica tube under vacuum and annealed in a furnace at 1100 °C for 96 h.
Powder X-ray Diffraction (PXRD): The powder sample was ground with a mortar and pestle and sieved through a 100-mesh screen for X-ray diffraction measurements. The fine powder was taken on a zero background off-axis SiO2 plate by using solvent-smearing techniques with ethanol. PXRD experiments were performed using a Bruker D8 ADVANCE ECO instrument at room temperature. Data were collected from 15° to 80° 2θ with a step size of 0.01638° 2θ using Cu Kα1 and Kα2 radiations with Ni filter to remove Cu Kb.
Spark Plasma Sintering: The finely ground powder was loaded into a 12.7 mm internal diameter graphite die (Cal Nano) with graphite plungers and graphite foils on each side inside an argon atmosphere within the glove box. The die was then inserted into a spark plasma sintering device (Dr. Lab Sinter Jr., Fuji Corp.) for pressing under a 50% Air/Ar environment. The powder was heated to 850 °C over 10 minutes, with the applied force increasing from 6 to 10.5 kN during this period. It was then sintered to 900 °C in 1 minute and held at this temperature for 30 minutes to consolidate the sample. The resulting pellets achieved densities greater than 98% of the theoretical density, as measured by the Archimedes method.
Resistivity Measurements: Resistivity measurements were conducted on densified pellets with a diameter of 12.7 mm at the Jet Propulsion Laboratory (JPL) using a Van der Pauw method. Resistivity was converting into conductivity for the data analysis.
Seebeck Coefficient Measurements: The Seebeck coefficient was measured at the Jet Propulsion Laboratory (JPL) using a custom-built apparatus generating light pulses via the light-pipe methods with tungsten-niobium thermocouples under high vacuum.
Thermal Conductivity Measurements: The thermal diffusivity of the pressed pellet was measured from 298 K to 1272 K using a Netzsch LFA-457 unit. The dense pellet was polished to achieve a uniform, consistent thickness. It was coated with graphite to ensure high emissivity of the laser flash. The total thermal conductivity, k, was calculated from the equation k = DCpd, where D is the measured diffusivity; Cp is the heat capacity; d is the room temperature density obtained from the Archimedes method. Heat capacity was estimated using the Dulong−Petit law.
Carrier Concentration and Hall Mobility: Hall coefficient measurements were conducted on densified pellets with a diameter of 12.7 mm at the Jet Propulsion Laboratory (JPL) using a Van der Pauw method with a applied magnetic field of 1.0 T and a current of 100 mA.
Files and variables
File: Data.zip
File Description: The file contains 4 data sets corresponding to the 4 compositions measured, saved as both *.xlsx and *.csv files. The files are named according to the composition: Eu14MgAs11, Eu14CdAs11, Eu14ZnAs11, and Eu14Zn1.2As11
Data Description: Each file contains PXRD (2-theta (°), intensity (arbitrary units)); Conductivity vs T (Temperature (K), Conductivity (S cm -1); Seebeck vs T (Temperature (K), Seebeck Coefficient (µV/K)); Carrier Concentration vs T (Temperature (K), Carrier Concentration (h+ , cm -3)), and Hall Mobility vs T (Temperature (K), Hall Mobility (cm2 V -1 s -1).