Transformation of fluorite δ-Bi2O3 into a new tetragonal phase.

Bismuth oxide kinetically stabilized by doping with a metastable structure of disordered fluorite δ-Bi2O3 has a unique conductivity. Oxygen selective membranes at intermediate temperatures ~550 °C, on the base of cermet δ-Bi2O3/Ag, have the highest potential for air separation and can be used to produce oxygen for distributed multigeneration by burning fossil carbon fuels. When searching for the optimal composition of δ-Bi2O3, the degradation of fluorite into a new tetragonal phase was discovered in ceramics synthesized using mechanical activation. The tetragonal phase is formed and exists in a topotaxial composite with the fluorite structure. For a relatively stable over a wide temperature range tetragonal phase with a = 0.3854, c = 0.88905 nm, S.G. P-4, crystal structure and atomic coordinates have been proposed. In samples of fluorite and topotaxial composite, the Raman and Mössbauer spectra were recorded and discussed. The discovery of a new tetragonal phase of doped bismuth oxide and its existence area makes it possible to optimize the composition and the synthesis of a more stable solid electrolyte δ-Bi2O3 with high conductivity. [ABSTRACT FROM AUTHOR]