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A2: Medium temperature materials
The AgSbTe2- compound is a derivative of the promising lead-antimony-silver-tellurium class of materials, namely LAST, exhibiting good thermoelectric (TE) performance at the mid-temperature range. Introducing second-phase precipitates as well as lattice point defects to these base alloys is expected to reduce their lattice thermal conductivity, thereby increasing the figure of merit, ZT.
In this study we perform lattice dynamics first-principles calculations for the AgSbTe2-phase , and estimate the stability of its three polymorphs at a wide temperature range from 0 up to 600 K. We calculate the vibrational density of states of the AgSbTe2 (P4/mmm)-polymorph, suggesting that the formation of substitutional defects at the Ag-sublattice sites impedes lattice vibrations, thereby reducing its lattice thermal conductivity. Herein, we focus on calculations of the La0.125Ag0.875SbTe2 compound based on the Debye approximation, and predict the reduction of the average sound velocity from 1684 to 1563 m·s-1 due to La-doping, which is manifested by ca. 14 % reduction in thermal conductivity. To validate the computational results, we produce two Ag-Sb-Te-based alloys: a ternary (without La additions), and a quaternary, La-alloyed one. We measure the thermal conductivity of both alloys using the laser flash analysis (LFA) method, and observe reduction in thermal conductivity as a result of La-alloying from a value of 0.92 to 0.71 W·m-1·K-1 at 573 K, as calculated from first-principles.