Systematic study of the structural, electronic, optical and thermoelectric properties of AHfO3(A = Ca, Ba) perovskites at various pressure using ab-initio calculations

The present study investigates the pressure dependence of the structural, elastic and electronic aspects for specifying the optical and thermoelectric device applications of alkaline rare-earth hafnate AHfO3(A = Ca, Ba) perovskites. The calculations have been performed by employing the all electron FP-LAPW+lo method. The PBEsol-GGA functional has been applied for treatment of the exchange-correlation energy. Using structural optimization, the lattice constants of the stable cubic phases are extracted, which are in good match with the existing theoretical and experimental literature. The cubic elastic constants (D11, D12 and D44), bulk moduli (B) are computed for evaluating the mechanical strength against external pressure up to 15 GPa. The electronic properties reveal that Hf-3dstates primarily construct conduction band minima, while O-2p states construct valance band maxima at 0 GPa, exhibiting an indirect bandgap (-M), which has been transformed to direct bandgap (-) at 15 GPa. Investigations of the optical properties illustrate that change in pressure can tune the optical parameters of these materials within ultra-violet (UV) energies suggesting commercial optoelectronic utilities. Our analysis shows that BaHfO3 exhibits better thermoelectric properties than CaHfO3 at room temperature whereas, thermoelectric performance both the compounds become comparable at higher temperature.