Group-I lead oxide X$_2$PbO$_3$ (X=Li, Na, K, Rb, and Cs) glass-like materials for energy applications: A hybrid-DFT study
Pb-based compounds have garnered considerable theoretical and experimental attention due to their promising potential in energy-related applications. In this study, we explore the glass-like alkali metal lead oxides X$_2$PbO$_3$ (X=Li, Na, K, Rb, Cs) and assess their suitability for piezoelectric and thermoelectric applications. First-principles calculations were performed using hybrid density functional theory (DFT), incorporating B3LYP, HSE06, and PBE0 functionals. Among these, PBE0 is identified as the most accurate, yielding lattice parameters in close agreement with experimental data. Structural stability was confirmed through evaluation of thermal, mechanical, and formation energies. For the non-centrosymmetric orthorhombic phase Cmc2$_1$-X$_2$PbO$_3$ (X=K, Rb, Cs), piezoelectric constants were computed via both the numerical Berry phase (BP) method and the analytical Coupled Perturbed Hartree-Fock/Kohn-Sham (CPHF/KS) formalism. Notably, Cs$_2$PbO$_3$ exhibited a piezoelectric coefficient of e$_{33}$ = 0.60 C m$^{-2}$ (CPHF/KS), while K$_2$PbO$_3$ showed e$_{32}$ = -0.51 C m$^{-2}$ (BP). Thermoelectric properties were investigated using the semiclassical Boltzmann transport theory within the rigid band approximation. The calculated thermoelectric performance reveals promising figures of merit (ZT), ranging from 0.3 to 0.63, suggesting these materials are applicable as future thermoelectric materials.