New anion-conducting solid solutions Bi1−xTex(O,F)2+δ (x > 0.5) and glass–ceramic material on their base

The anion-excess fluorite-like solid solutions with general composition Bi1−xTex(O,F)2+δ (x > 0.5) have been synthesized by a solid state reaction of TeO2, BiF3 and Bi2O3 at 873 K with following quenching. The homogeneity areas and polymorphism of the I ↔ IV Bi1−xTex(O,F)2+δ phases were investigated. The crystal structure of the low temperature IV-Bi1−xTex(O,F)2+δ phase has been solved using electron diffraction and X-ray powder diffraction (a = 11.53051(9) Å, S.G. Ia-3, RI = 0.046, RP = 0.041). Glass formation area in the Bi2O3–BiF3–TeO2 (10% TiO2) system was investigated. IVBi1−xTex(O,F)2+δ phase starts to crystallize at short-time (0.5–3 h) annealing of oxyfluoride glasses at temperatures above Tg (600–615 K). The ionic conductivity of the crystalline Bi1−xTex(O,F)2+δ phase and corresponding glass-ceramics was investigated. Activation energy of conductivity Ea = 0.41(2) eV for the IV-Bi1−xTex(O,F)2+δ crystalline samples and Ea = 0.73 eV for the glass-ceramic samples were obtained. Investigation of the oxyfluoride samples with a constant cation ratio demonstrates essential influence of excess fluorine anions on the ionic conductivity.

The homogeneity areas and polymorphism of anion-excess fluorite-like solid solutions with general composition Bi1−xTex(O,F)2+δ (x > 0.5) have been investigated. Their crystallographic and structural characterization have been conducted. The influence of chemical composition on ionic conductivity both in crystalline and glass–ceramic forms has been determined.Figure optionsDownload as PowerPoint slideHighlights
► The homogeneity areas and polymorphism of the Bi1−xTex(O,F)2+δ (x > 0.5) phases have been investigated.
► The crystal structure of the low temperature IV-Bi1−xTex(O,F)2+δ phase has been determined.
► The ionic conductivity of the crystalline Bi1−xTex(O,F)2+δ phase and glass–ceramic samples has been studied.