Strain-driven electronic and thermoelectric modulation in Cs2CuMoX6 (X = Cl, Br) halide double perovskites

Halide-based double perovskites under biaxial strain propose a profound insight into their electronic and magnetic characteristics and emerge as a potential aspirant for spintronic applications. In this examination, the structural, electronic, magnetic, optoelectronic, and thermoelectric characteristics of Cs₂CuMo (Cl/Br)₆ have been studied under biaxial strain by employing the WIEN2k software. The lattice constant value has been enhanced from 10.01 to 10.53 Å by substituting Cl with Br for an optimized FCC lattice. Their thermodynamic stability is affirmed by the computed values of enthalpy of formation i.e., −1.46 eV for Cs₂CuMoCl₆ and -1.33 eV for Cs₂CuMoBr₆. The bandgap value is noticed as 0.94 and 0.32 eV for Cs₂CuMoCl₆ and Cs₂CuMoBr_6, respectively, when calculated using GGA, and this bandgap increased to 2.25 and 0.93 eV when computed using GGA + mBJ. The integration of Hubbard's potential in the range of 1–5 eV further improves their bandgap to 2.38 eV (@1eV) to 2.58 eV (@5eV) for Cs₂CuMoCl₆ and 0.96 eV (@1eV) to 1.09 eV (@5eV) for Cs₂CuMoBr₆. The compressive strain consistently reduces the bandgap, whereas tensile strain widens the bandgap till 3 %, which reduces on further increment of tensile strain to 5 % for Cs₂CuMoCl₆. The Mo magnetic moments and spin magnetization density at iso-value ±0.05 eÅ slightly vary under strain. The biaxial strain ranging from 0 to 4 % has been employed along with the GGA + mBJ potential to compute the optoelectronic and thermoelectric characteristics, underscoring their potential for transport and energy harvesting implementations.