Investigations of electronic and thermoelectric properties of half-Heusler alloys XMgN (X = Li, Na, K) by first-principles calculations

The rapid depletion of the fossil fuels and their environment repercussion can be resolved wisely by exploring the efficient and sustainable materials which have the ability to convert waste heat into electricity. Half-Heusler materials are also considered one of the promising class for the thermoelectric applications. In this paper, the investigations on the thermoelectric properties of half-Heusler compounds, XMgN (X = Li, Na, K) are reported. The study is carried out within full potential linearised augmented plane wave plus local orbital approach (FP-LAPW + lo) in conjunction with the semi-empirical Boltzmann theory. To incorporate exchange-correlation energy/potential part, Perdew and Wang (PW) suggested local density approximation (LDA), parameterized generalized gradient approximation (GGA) by Perdew-Berke-Ernzerhof (PBE) and the modified Becke-Johnson (mBJ) exchange potential by Trans-Blaha are used. Our electronic band structure calculations show that the KMgN is indirect band gap material, whereas LiMgN and NaMgN demonstrate their direct electronic band gap structure. To comprehend their thermoelectric character, the calculations of the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit (ZT) are carried out at temperatures of values 300 K, 600 K, and 900 K. From our calculations, the optimal value of Seebeck coefficient for the all three materials although was found at 300 K, the results of the Seebeck coefficient for the LiMgN were found more good as compared to NaMgN and KMgN and in coordination with the Lee et al. study as well. Similarly, electrical conductivity results endorse the Wiedemann-Franz law. The calculated results of the ZT parameter (ZT ~ 1) for the all three materials (LiMgN, NaMgN, and KMgN) revealing that the investigated materials have a potential to be used for thermoelectric applications