Effects of Octahedral Tilting on the Site of Substitution of Manganese in CaTiO3

Abstract Electron paramagnetic resonance (EPR) and X-ray absorption fine structure measurements were combined with first principles calculations to investigate the substitutional behavior of Mn ions in perovskite CaTiO3 ceramics. While transition-metal dopants in perovskite-structured oxides often act as aliovalent defects, Mn in CaTiO3 is amphoteric and concurrently occupies both Ca and Ti sites as Mn2+ and Mn4+, respectively. Contrary to the behavior of Mn in SrTiO3 and BaTiO3, which exhibit larger geometric perovskite tolerance factors, in CaTiO3, it is determined that Mn2+ prefers A-site substitution. Density functional theory (DFT) calculations provide insight to the unique defect chemistry of Mn-doped CaTiO3 compared to SrTiO3 and BaTiO3, highlighting the role of octahedral rotations which accommodate ionic size mismatch between the larger host and smaller dopant cations on the cuboctahedral sites without significant dopant-ion displacements. Superposition models of the EPR zero-field splitting parameters for multiple types of Mn defect centers were considered based on the structural parameters of DFT calculations, and these results, combined with the EPR, DFT, and X-ray absorption analysis, were used to determine the point defect substitution mechanisms of Mn-CaTiO3.