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

Abstract

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 H₂/He shows that NiO phase segregates and reduces to give a high dispersion of Ni metal particles on the SrTiO₃ oxide.