Transport and optical study of mechanically stable novel RNiSb (R= Tb, Dy, Tm) half-Heusler compounds for thermoelectric and optoelectronic applications

Abstract

Spin polarised calculations using the GGA+U method, has been performed for the study of structural stability, electronic, mechanical, thermodynamic, and thermoelectric behavior of half-Heusler compounds RNiSb (R= Tb, Dy, Tm). The calculated formation energy ensures the thermodynamic stability and fulfilment of Born-Huang criteria confirms the mechanical stability of the studied compounds. An indirect narrow energy gap of 0.11, 0.16 and 0.54 eV for RNiSb (R= Tb, Dy, Tm) half-Heusler, respectively, is found to open up using GGA+U calculations. The brittle nature of these compounds is also validated by the calculated values of Pugh’s ratio and Cauchy pressure. Our calculated optical spectra of these compounds suggest feasibility for application as optoelectronic devices operating in the visible and near ultraviolet spectrum. High value of the calculated melting temperature (around 1400 K) as well as experimental observations of thermoelectric properties up to 1000K, confirms the mechanical stability of these RNiSb compounds at elevated temperatures. We obtained high values of Seebeck coefficient, which is consistent with the experimental data. Therefore, these compounds are suitable as potential candidates for high temperature thermoelectric applications.