Pressure-driven thermoelectric properties of defect chalcopyrite structured ZnGa₂Te₄: ab initio study

The pressure induced structural, electronic, transport, and lattice dynamical properties of ZnGa₂Te₄ were investigated with the combination of density functional theory, Boltzmann transport theory and a modified Debye-Callaway model. The structural transition from I4̄ to I4̄2m occurs at 12.09 GPa. From the basic observations, ZnGa₂Te₄ is found to be mechanically as well as thermodynamically stable and ductile up to 12 GPa. The direct band gap of 1.01 eV is inferred from the electronic band structure. The quantitative analysis of electron transport properties shows that ZnGa₂Te₄ has moderate Seebeck coefficient and electrical conductivity under high pressure, which resulted in a large power factor of 0.63 mW m^-1 K^-2 (750 K). The ultralow lattice thermal conductivity (∼1 W m^-1 K^-1 at 12 GPa) is attributed to the overlapping of acoustic and optical phonon branches. As a result, the optimal figure of merit of 0.77 (750 K) is achieved by applying a pressure of 12 GPa. These findings support that ZnGa₂Te₄ can be a potential p-type thermoelectric material under high pressure and thus open the door for its experimental exploration.