Confluence of structural distortion and A -site composition in the band gaps of perovskite niobate and tantalate photocatalysts

Abstract

The effects of structural distortion and $A$-site composition on the band gaps and band-edge orbitals of perovskite niobate and tantalate photocatalysts are explored using density-functional theory and crystal-field theory. When filled $d$ orbitals are introduced to the $A$ site by replacing alkali metal cations with silver, the crystal-field splitting energies of the $A$-site $d$ orbitals play a dominant role in determining the effect of silver in narrowing the band gap. It is demonstrated that an intuitive, geometry-based metric can usually predict within 0.1 eV the extent to which the presence of silver narrows the band gap. The ability to make such predictions is both valuable and potentially generalizable toward the design of photocatalysts.