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Effects of Octahedral Tilting on the Site of Substitution of Manganese in CaTiO 3

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Document pages: 38 pages

Abstract: Electron-paramagnetic-resonance and X-ray absorption fine structure measurements were combined with first principles calculations to investigate the substitutional behavior of Mn ions in perovskite CaTiO3ceramics. While transition-metal dopants in perovskite-structured oxides often act as aliovalent defects, Mn in CaTiO3 is amphoteric and regardless of processing conditions concurrently occupies both Ca and Ti sites as Mn2+ and Mn4+, respectively. Contrary to the redox behavior of Mn in SrTiO3 and BaTiO3, which exhibit larger geometric perovskite tolerance factors, in CaTiO3, high-temperature treatments under reducing conditions do not transform Mn4+ to Mn2+. Density functional theory 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 any significant dopant-ion displacements.

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