Thermoelectric Properties of Heusler X₂CsBi Alloys (X = Li, Na, K, and Rb) as a Prospect for Use in Peltier Effect Based Cooling Devices

Thermoelectric properties of Heusler X₂CsBi alloys (X = Li, Na, K, and Rb) were studied by the AICON2 software based on the density functional theory integrated into the VASP software package for calculation of electronic properties and by the PHONOPY software for calculation of phonon properties. The calculations were carried out by the SCAN functional. For all the studied compounds, low values less than 1 W/(m K) were obtained for the lattice thermal conductivity λ_lat throughout the entire temperature range. For Li₂CsBi, Na₂CsBi, K₂CsBi, and Rb₂CsBi, λ_lat at room temperature was 1.12, 0.25, 0.32, and 0.21 W/(m K), respectively. It has been shown that the thermoelectric quality factor ZT at room temperature is 0.21, 0.28, and 0.72 for Li₂CsBi, Na₂CsBi, and Rb₂CsBi in the case of p-type doping (holes). For K₂CsBi doped with electrons (n-type), ZT = 0.14 at room temperature. High thermoelectric efficiency values make these alloys promising materials for thermoelectric applications at room temperatures. The difference between thermoelectric quality factor values after n- and p-type doping can be used to create Peltier effect based cooling devices.