CRYSTAL STRUCTURE OF THE COMPOUND BI₃.₄₃RE₀.₅₇O₆.₂₉

Abstract

The work investigates the crystal structure of a non-stoichiometric oxide compound of the composition Bi₃.₄₃Re₀.₅₇O₆.₂₉, belonging to the Bi₂O₃–Re₂O₇ system, which attracts considerable attention due to its high oxide-ionic conductivity and prospects for use in solid-state electrochemistry. The relevance of the study is due to the need to search for new materials with improved transport properties, in particular for use in solid oxide fuel cells and oxygen sensors. The aim of the work is to establish the features of the crystal structure, cation ordering and state of the oxygen sublattice of the studied compound. To achieve this goal, the X-ray powder diffraction method was used with subsequent refinement of the structure by the Rietveld method. The samples were obtained by melting the starting oxides with subsequent quenching, which ensured the formation of a single-phase material. As a result of the study, it was established that the compound Bi₃.₄₃Re₀.₅₇O₆.₂₉ crystallizes in the structural type δ-Bi₂O₃ with cubic symmetry and space group Fm3̅m. The unit cell parameter a = 5.7363(1) Å was determined. It was shown that Bi and Re atoms statistically occupy one crystallographic position, which indicates their partial mutual substitution in the cation sublattice. It was established that the oxygen sublattice is characterized by partial filling of positions, which indicates the presence of a significant number of oxygen vacancies. These vacancies play a key role in the formation of high oxide ionic conductivity, creating effective migration paths for oxygen ions. The non-stoichiometric composition contributes to additional structural defects and stabilization of the high-temperature δ-phase at room conditions. The obtained results are consistent with the literature data and confirm that the studied compound belongs to the class of defective fluorite-like oxides. The revealed structural features, in particular the disorder of the oxygen sublattice and the statistical distribution of cations, determine the prospects of the material as an effective oxide-ionic conductor. The work expands the understanding of the mechanisms of defect structure formation in oxides of the Bi–Re–O system and can be used for further targeted synthesis of new functional materials.