Substitutional Point Defect Mechanisms and Structural Relaxations for Manganese in SrTiO3: Bridging the Metrology Concentration Gap

Published

May 7, 2020

Author(s)

Russell Maier, Igor Levin, Eric J. Cockayne, Matthew P. Donohue, Giannantonio Cibin

Abstract

The methodology for experimentally verifying the point-defect chemistry (site of substitution, valence, and chargecompensation mechanisms) in manganese-doped SrTiO3 ceramics is presented for dilute and nondilute dopant concentrations. Experimental and theoretical techniques have strengths and weaknesses depending upon defect types and concentrations, so a combinatorial-characterization approach is required. Using electron-paramagnetic resonance and X-ray-absorption fine-structure measurements combined with density functional theory calculations, the charge-compensation mechanisms and local structural relaxations for five unique manganese defect centers are identified. Mn4+, as an isovalent dopant, occupies the octahedrally coordinated Ti sites without the need for charge compensation; its smaller ionic radius relative to Ti is accommodated by isotropic contraction of the [MnO6] octahedra. Mn3+ is an aliovalent dopant that also favors the Ti sites with the [MnO6] octahedra exhibiting Jahn−Teller distortions. The charge difference associated with the Mn3+ Ti4+ substitution is compensated by formation of oxygen vacancies. A more complex behavior is observed for the Mn2+ species, which can occupy either the Sr or Ti sites depending on the Sr/Ti ratio. The effects of Mn concentration or hightemperature annealing on the site preference (i.e., Sr vs Ti) are negligible. The Mn2+ species on the Sr sites are strongly off-centered in the relatively large cuboctahedral cages within the oxygen framework. The dynamic nature of the Mn displacements in these configurations is confirmed using ab initio molecular dynamics simulations.

Citation

Journal of Materials Chemistry A

Pub Type

Journals

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DOI Link

Keywords

Perovskite, Electron Paramagnetic Resonance, X-Ray Absorption, Density Functional Theory

Citation

Maier, R. , Levin, I. , Cockayne, E. , Donohue, M. and Cibin, G. (2020), Substitutional Point Defect Mechanisms and Structural Relaxations for Manganese in SrTiO3: Bridging the Metrology Concentration Gap, Journal of Materials Chemistry A, [online], https://doi.org/10.1021/acs.chemmater.0c01082 (Accessed May 2, 2024)