A theoretical investigation of 18-electron half-Heusler tellurides in terms of potential thermoelectric value

Half-Heusler tellurides (M-IV M-VIII Te, where M-IV = Ti, Zr, Hf, and M-VIII = Fe, Ru, Os) with 18 valence electrons were the subject of theoretical predictions from first principles. Eight novel compounds are predicted by the MBJGGA approach to be semiconductors, with band gaps ranging from 0.395 eV (ZrOsTe) to 1.247 eV (ZrRuTe). The band gaps, spin-orbit split-offs of heavy- and light-hole bands, and effective masses in the half-Heusler tellurides are carefully analyzed. Some chemical trends are disclosed, e.g., the Fe-bearing compounds exhibit the widest band gaps among the studied systems. ZrOsTe and HfRuTe are expected to be candidate materials for applications in thermoelectric devices due to the Mahan's '10 kBT rule'. The thermoelectric performance is discussed based on the results of transport calculations. Very high values of figure of merit (ZT) are predicted within MBJGGA, with maximums of 2.76 and 4.14 at 1100 K for ZrOsTe and HfRuTe, respectively. Slightly lower ZT (3.65) at 1100 K was obtained within GGA for HfRuTe. Some trends in GGA-MBJGGA results among different temperature ranges are shown and discussed. The results obtained encourage further theoretical and experimental studies on half-Hesler tellurides.