Abstract
Tysonite solid solutions Bi1−x Ba x O y F3−x−2y in the BiF3-BiOF-BaF2 system were obtained by solid-phase synthesis in sealed copper tubes in an argon atmosphere at 873 K with subsequent quenching. The solid solutions were studied by X-ray diffraction, electron diffraction, and impedance spectroscopy. On the basis of X-ray powder diffraction data, the homogeneity ranges of the tysonite solid solutions were determined and the scheme of their location in the BiF3-BiOF-BaF2 system at 873 K was suggested. Aliovalent substitutions in both the cation and anion sublattices Ba2+ → Bi3+ and O2− → F− made it possible to vary the concentration of anion vacancies. It was found that, at a high concentration of anion defects at 873 K, the hexagonal tysonite modification with space group P63/mmc is stable. With a decrease in the defect concentration, the trigonal tysonite modification with space group $$ P\bar 3c1 $$ becomes stable. An ordered monoclinic tysonite-type modification BiO y F3 − 2y (0.13 < y < 0.23) was revealed. For the homogeneity ranges of all tysonite phases, dependences of the unit cell parameters and conductivity on the composition along the sections with a constant barium or oxygen content were reported. The most probable location of oxygen anions and anion vacancies in the tysonite structure is discussed.
Published Version
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