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Substitutional mechanisms and structural relaxations for manganese in SrTiO3: Bridging the concentration gap for point-defect metrology

DOI: 10.1021/acs.chemmater.0c01082 DOI Help

Authors: Russell A. Maier (National Institute of Standards and Technology) , Eric Cockayne (National Institute of Standards and Technology) , Matthew Donohue (National Institute of Standards and Technology; University of Maryland) , Giannantonio Cibin (Diamond Light Source) , Igor Levin (National Institute of Standards and Technology)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: May 2020
Diamond Proposal Number(s): 16478

Abstract: The methodology for experimentally verifying the point-defect chemistry (site of substitution, valence, and charge compensation mechanisms) in manganese-doped SrTiO3 ceramics is presented for dilute and non-dilute 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 high-temperature 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.

Subject Areas: Chemistry, Materials

Instruments: B18-Core EXAFS