Unraveling the thermoelectric properties of Zr0.5Hf0.5YZ (Y = Ni, Co, Pd and Z = Sn, Sb, Bi) half-Heusler alloys
Parul R. Raghuvanshi1#, Amrita Bhattacharya1
1Computational Materials Simulation Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai
#Presenting author: parul_raghuvanshi[at]iitb.ac.in; Phone: +91 22 2576 7620
ABSTRACT
Thermoelectrics can be an alternative to a green energy economy via waste heat recovery given that more than 60% of the produced energy is lost in the form of waste heat worldwide [1]. The dimensionless figure-of-merit (ZT = TS2σ/κ, Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ) and T is the absolute temperature) drives the thermoelectric efficiency. Half- Heusler (HH) compounds (XYZ, where X and Y are transition metals and Z is a main group element) have emerged as promising thermoelectric materials with tunable band gap that offers huge chemical space to optimise their thermoelectric performance [2]. In this work, we employ density functional theory calculations to explore the electronic structures of Zr0.5Hf0.5YZ (Y = Ni, Pd, Co and Z = Sb,
Sn, Bi) compositions using semi-local and hybrid calculations including spin orbit coupling (SOC) into account. We compare the valley degeneracies and the electronic effective mass at the valence band maximum and conduction band minimum. The compositions are found to have narrow electronic band gap in the range of ~0.4 -1.0 eV. Our results show that inclusion of SOC does not affect the valley degeneracies of these compositions, which make them interesting for thermoelectric application. We calculate the transport coefficients and compare the power factor (PF = S2σ) of the compounds using semi-classical Boltzmann transport theory. Furthermore, we investigate and elucidate on the lattice thermal conductivity of these compositions by employing harmonic and anharmonic vibrational calculations using phonopy and phono3py.
Keywords: Half-Heusler compounds, thermoelectric properties, density functional theory.
References:
[1] T. M. Tritt, Science, 283, 804-805 (1999).
[2] J. Zhang, X. Zhang, Xiwen and Y. Wang, Scientific Reports, 7, 14590 (2017).