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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 Bi 1.5 Cr 0.5 Ti 2 O 7 (Bi site doping) in a fine powder state was shown via coprecipitation method, while the single-phase Bi 2 Ti 1.5 Cr 0.5 O 7 (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 1.5 Cr 0.5 Ti 2 O 7 compound is an A-site deficient pyrochlore (Bi 1.38 Cr 0.30 )-(Ti 1.84 Cr 0.16 )O 6.44 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 1.6 Cr 0.1 Ti 2 O 7−δ ) and 3.01 μB (Bi 1.5 Cr 0.5 Ti 2 O 7 ) was experimentally observed. All chromium in magnetically diluted pyrochlore Bi 1.6 Cr 0.1 Ti 2 O 7−δ exists in the form of Cr 3+ monomers, whereas in the more concentrated magnetic Bi 1.5 Cr 0.5 Ti 2 O 7 composition Cr 3+ -O-Cr 3+ 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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