Site-Selective Doping and Rational Band Engineering through Coupled Structural, Electronic, and Orbital Analysis in Multi-Site Oxides

Site-selective doping in structurally complex oxides remains challenging due to multiple inequivalent cation sites and distinct coordination environments. Here, we present a strategy that couples advanced structural characterization, DFT calculations, and molecular orbital analysis to achieve site-selective doping and rational band engineering in SrGa₁₂O₁₉, a magnetoplumbite-type oxide featuring five distinct Ga sites. High-resolution PXRD combined with DFT calculations reveal that In³⁺ preferentially occupies the Ga4 (octahedral) and Ga3 (tetrahedral) sites, modulating the conduction band minimum (CBM) via M3-O antibonding interactions. This site-selective doping reduces the band gap from 4.54 to 4.23 eV (SrGa₁₀In₂O₁₉), enhancing photocatalytic H₂ evolution rate from 10.5(3) to 34.8(5) μmol/h. The in-depth analysis of doping-induced structural evolution reveals how local stress propagates and is relieved through bond-length variations and atom displacements. For instance, In³⁺ at M4 causes octahedral expansion and c-axis elongation via Coulomb repulsion, while adjacent units undergo compensatory compression. In³⁺-doping at M3 similarly exerts mechanical stress on neighboring Ga1 polyhedra, revealing a mutual constraint mechanism that limits complete solid-solution formation. This spatial interdependence explains site preferences and highlights the role of structural voids in enabling selective incorporation. This study offers a generalizable strategy for designing semiconductors with tailored band structures through site-selective doping.