First-principles study of XGeO3 (X = Zn, Cd): Semiconducting perovskites for optoelectronic and thermoelectric applications

The structural, mechanical, electronic, thermodynamic, optical, and thermoelectric properties of zinc germanate (ZnGeO3) and cadmium germanate (CdGeO3) are theoretically predicted using first-principles calculations based on density functional theory (DFT). We examined the crystal and electronic band structures, as well as optical and thermoelectric properties. Both compounds have the perovskite structure with lattice parameters of 3.68 Å for ZnGeO3 and 3.74 Å for CdGeO3. The ZnGeO3 is more stable, with a minimal energy of 15832.079 Ry versus 15832.062 Ry for CdGeO3. The electronic band structure shows direct bandgaps of 2.8 eV for ZnGeO3 and 3.1 eV for CdGeO3, confirming their semiconducting nature. The calculated optical properties include the dielectric function and absorption coefficient. CdGeO3 has higher absorption peaks within the UV range. Thermoelectric performance is moderate, with the figure of merit values of 0.53 for ZnGeO3 and 0.59 for CdGeO3 at room temperature. These compounds show promise for optoelectronic applications, while their thermoelectric efficiency remains limited.