Journal
INORGANIC CHEMISTRY
Volume 58, Issue 15, Pages 9904-9915Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.9b01057
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Funding
- [ISSC UB RAS 0397-2019-0003]
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Combined ab initio and experimental study of Cr doping into bismuth titanate pyrochlore was carried out for the first time. Accurate firstprinciples density functional theory calculations were performed considering a Hubbard U correction (DFT+U) to account for on-site Coulomb interactions of the Cr 3d states. The possibility to synthesize a novel pyrochlore-type compound with a high dopant content Bi15Cr0.5Ti2O7 (Bi site doping) in a fine powder state was shown via coprecipitation method, while the single-phase Bi15Cr0.5Ti2O7 (Ti site doping) could not be obtained. Detailed descriptions of thermostability, structural, optoelectronic, and magnetic properties of Cr-doped pyrochlores in the fine (particles size 100-300 nm) and bulk (1-50 mu m) powder states are presented based on the well-matched results of theoretical and experimental investigations. According to the Rietveld refinement of the X-ray diffraction data, Bi15Cr0.5Ti2O7 compound is an A-site deficient pyrochlore (Bi1.38Cr0.30)-(Ti1.84Cr0.16)O-6.44 with chromium distribution between both cationic sites. Metastabilitym of fine powder Cr-containing pyrochlore phase was revealed during long-thermal annealing, while the bulk powder sample was stale up to its melting point 1230 degrees C. According to the study of electronic structure and optical properties, Cr-doped pyrochlores are wide-band semiconductors with light absorption in the range of 300-500 nm and perspective as photocatalytic active materials under visible light irradiation. Paramagnetic behavior with effective magnetic moment 3.92 mu B (Bi1.6Cr0.1Ti2O7-delta) and 3.01 mu B (Bi15Cr0.5Ti2O7 ) was experimentally observed. All chromium in magnetically diluted pyrochlore Bi1.6Cr0.1Ti2O7-delta exists in the form of Cr3+ monomers, whereas in the more concentrated magnetic Bi15Cr0.5Ti2O7 composition Cr3+-O-Cr3+ dimers may also be present, with a fraction equal to 0.39. This investigation constitutes the first approach to the electronic, structural, optical, and magnetic properties of d-elements doped bismuth titanate pyrochlores from experimental and theoretical viewpoints, emphasizing the power of DFT+U to provide insights and to complement the experimental characterization of these new compounds.
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