DFT study on the effect of hydrostatic pressure on thermoelectric properties of the double perovskites Rb2SeX6 (X=Cl, Br).

Abstract

Due to their diverse physical properties and customisable crystal structures, double perovskite materials have become attractive options for multifunctional applications. For energy conversion their thermoelectric properties are very desirable. The effect of hydrostatic pressure (0–8 GPa) on the thermoelectric properties of the double perovskites Rb₂SeX₆ (X=Cl, Br) was investigated in this work using a density functional theory approach. Norm conserving pseudo potentials implemented in the plane wave basis set of the quantum espresso code was employed in this study. The exchange correlation functional used was the Generalised Gradient Approximation of Perdew Bulk Ezenhorp (GGA-PBE). From the results of thermoelectric properties, the Seebeck coefficients (S) shows that at 0 GPa, S have higher values than at higher hydrostatic pressures (2–8 GPa). Compared to Rb₂SeCl₆ (0.227 X 10³ m V/K), Rb₂SeBr₆ (0.252 X 10³ m V/K) has higher values of S. According to the figure merit (ZT) results, the hydrostatic pressure affects the ZT values; the ZT values drop as the pressure rises. In the calculations, the lowest temperature (150 K) produced the highest ZT values. ZT values for Rb₂SeBr₆ (3.9) are greater than those for Rb₂SeCl₆ (3.70). The ZT values in this work surpass unity, indicating that the double perovskite materials Rb₂SeCl₆/Br₆ under study have high ZT values for thermoelectric device engineering. Also from the results, Rb₂SeBr₆ is a more effective thermoelectric material than Rb₂SeCl₆.

_{Keywords: DFT, Double perovskites, Hydrostatic Pressure, Thermoelectric properties, Seebeck coefficient, Figure of Merit.}