First-Principles Investigation of the Electronics, Optical, Mechanical, Thermodynamics and Thermoelectric Properties of Nabased Quaternary Heusler Alloys (QHAs) NaHfXGe (X=Co, Rh, Ir).

In this study, we explored the electronic and thermoelectric properties of the Na-based Quaternary Heusler Alloys (QHAs) NaHfXGe (X=Co, Rh, Ir) using DFT. We performed the spin-polarized DFT calculations at the GGA level and confirmed the ground state non-magnetic configuration of NaHfXGe. The mechanical and thermodynamical stabilities are analyzed and discussed to validate the stability by calculating the elastic constant and phonon dispersion curve. A thorough investigation on the electronic properties are carried out by performing the GGA, GGA+U, and GGA+SOC formalism where we report the semi-conducting characteristic of NaHfCoGe and NaHfRhGe QHAs. However, NaHfIrGe is predicted to be a non-magnetic metal. From the calculated optical properties we found that the most active optical absorption occurs within the Vis-UV region with α>105 cm-1, therefore the studied QHAs are proposed to be a promising optoelectronic materials. The results of the thermodynamic properties have shown that NaHfXGe follows Debye's low-temperature specific heat law and the classical thermodynamics of the Dulong-Petit law at high temperatures. The calculated thermoelectric efficiency using GGA+SOC formalism at T=1200 K are ZT 1.22 and 0.57 for NaHfCoGe and NaHfRhGe, suggesting that these materials are potential thermoelectric materials to operate at high temperature.&#xD.