Ab Initio and Experimental Insights on Structural, Electronic, Optical, and Magnetic Properties of Cr-Doped Bi 2 Ti 2 O 7

Combined ab initio and experimental study of Cr doping into bismuth titanate pyrochlore was carried out for the first time. Accurate first-principles density functional theory calculations were performed considering a Hubbard correction (DFT+U) to account for on-site Coulomb interactions of the Cr 3...

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Veröffentlicht in:Inorganic chemistry 2019-08, Vol.58 (15), p.9904-9915
Hauptverfasser: Krasnov, Aleksei G, Koroleva, Mariia S, Vlasov, Maxim I, Shein, Igor R, Piir, Irina V, Kellerman, Dina G
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Sprache:eng
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Zusammenfassung:Combined ab initio and experimental study of Cr doping into bismuth titanate pyrochlore was carried out for the first time. Accurate first-principles density functional theory calculations were performed considering a Hubbard 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 Bi Cr Ti O (Bi site doping) in a fine powder state was shown via coprecipitation method, while the single-phase Bi Ti Cr O (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 μm) 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, Bi Cr Ti O compound is an A-site deficient pyrochlore (Bi Cr )(Ti Cr )O with chromium distribution between both cationic sites. Metastability of fine powder Cr-containing pyrochlore phase was revealed during long-thermal annealing, while the bulk powder sample was stable up to its melting point 1230 °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 μB (Bi Cr Ti O ) and 3.01 μB (Bi Cr Ti O ) was experimentally observed. All chromium in magnetically diluted pyrochlore Bi Cr Ti O exists in the form of Cr monomers, whereas in the more concentrated magnetic Bi Cr Ti O composition Cr -O-Cr 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.
ISSN:0020-1669
1520-510X
DOI:10.1021/acs.inorgchem.9b01057