Dopant Distributions and Band-Edge Positions in Sr-Doped NaTaO3 : A First-Principles Study

Abstract

Sr doping is known to enhance the water-splitting activity of NaTaO₃ photocatalyst and is often accompanied by surface segregation of Sr, yet the electronic-structural origin remains unclear. Here, we employ first-principles calculations with explicit enumeration of all Sr configurations in bulk NaTaO₃ (NTO) and TaO₂-terminated (001) surfaces. In bulk, the enumeration shows that shorter Sr-Sr separations are energetically preferred. At surfaces, Sr segregates and accumulates strongly. Layer-resolved local density of states indicates that in-gap states are confined to the outermost TaO₂ layer, while interior layers retain a near-bulk gap. In Sr-rich surface layers, both band edges shift upward relative to the interior. Population analyses link the valence-band rise to O-O contraction and the conduction-band rise to Ta-Ta elongation. The Sr-doping and segregation yields near-surface band bending and a built-in electric field that can promote electron-hole separation and suppress recombination, rationalising the observed activity gains.