Thermodynamic approaches to determine the vacancy concentration in defective Nb1-xCoSb half-Heusler thermoelectric materials

The defective half-Heusler compound Nb1-xCoSb has been identified to be a promising thermoelectric material via modification of vacancies. Herein, we combined the experimental phase diagram with CALPHAD (CALculation PHAse Diagram) method to determine the vacancy concentration of Nb1-xCoSb in the equilibrium state, which is 0.17 <= x <= 0.22 at 1173 K and 0.17 <= x <= 0.2 at 1323 K and extrapolated to the whole composition and temperature range computationally. The calculated homogeneous region of the half-Heusler phase increases first and then decreases with increasing temperature, reaching a maximum Delta x = 0.042 at similar to 1123 +/- 20 K. The stoichiometric NbCoSb alloy is proved to locate at the binary-phase region of Nb1-xCoSb/Nb3Sb. This work opens a new avenue for understanding, design and preparation of thermoelectric materials. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The defective half-Heusler compound Nb1-xCoSb has been identified as a promising thermoelectric material through modification of vacancies. The equilibrium vacancy concentration of Nb1-xCoSb was determined using experimental phase diagram and CALPHAD method, and computationally extrapolated to the entire composition and temperature range.