Combined experimental and computational modelling studies of the solubility of nickel in strontium titanate

A combination of X-ray techniques and atomistic computational modelling has been used to study the solubility of Ni in SrTiO3 in relation to the application of this material for the catalytic partial oxidation of methane. The experiments have demonstrated that low temperature, hydrothermal synthesis is successful in preparing monophase, crystalline material with up to 5 atom % Ni doped in the octahedrally coordinated Ti4+ site of the SrTiO3 lattice. Computational modelling indicates limited solubility and identifies the most energy favoured Ni state as Ni2+ as opposed to Ni3+. However, modelling also suggests that thermodynamically Ni should occupy the Sr2+ site. This apparent contradiction is resolved by considering the kinetic effects operating during hydrothermal synthesis. An in situ EXAFS study of the thermal behaviour of Ni doped SrTiO3 in air and H-2/He shows that NiO phase segregates and reduces to give a high dispersion of Ni metal particles on the SrTiO3 oxide.