Thermoelectric properties of half-heusler LiMgN, NaMgN and KMgN alloys by first-principles

Abstract

Rapid fall of the fossil fuels and their implication towards environment can be reasonably resolved with the exploration of the efficient materials having the ability to convert wasted heat into electricity. In this regard, half-Heusler materials are reported as one of the promising class of the thermoelectric materials. In this research, mainly the investigations on the thermoelectric properties of half-Heusler XMgN (X=Li, Na, K) are done. The total energy calculations are performed using the full potential linearised augmented plane wave (FP-LAPW) method framed within density functional theory (DFT) and embodied in WIEN2k package, where the calculations of the thermoelectric properties are carried out by the same DFT based computational approach followed by the semi-empirical Boltzmann theory. However, to incorporate exchange-correlation energy/potential part, local density approximation (LDA) by Perdew and Wang (PW), parameterized generalized gradient approximation (GGA) of Perdew-Berke-Ernzerhof (PBE) and modified Becke-Johnson (mBJ) exchange potential by Trans-Blaha are used. From the calculations, it is found that the obtained results of lattice parameters are in good agreement with the previous calculations. From the electronic band structure analysis, LiMgN and NaMgN are found to be direct band gap materials whereas KMgN exhibits its indirect band gap make-up. The investigations for thermoelectric properties cover the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit (ZT) of the investigated materials at different temperatures such as 300K, 600K, and 900K. The calculated results of the ZT parameter for the LiMgN, NaMgN and KMgN (nearly equal to one i.e. ~1) reveal that all the investigated materials could be useful for thermoelectric applications.