Facile and reproducible method of stabilizing Bi 2O 3 phases confined in nanocrystallites embedded in amorphous matrix

Abstract

Bismuth sesquioxide (Bi 2O 3) draws much attention due to wide variety of phases in which it exists depending on the temperature. Among them, δ phase is specially interesting because of its high oxide ion conductivity and prospects of applications as an electrolyte in fuel cells. Unfortunately, it is stable only in a narrow temperature range ca. 730–830 ∘C. Our group has developed a facile and reproducible two-stage method of stabilizing Bi 2O 3 crystalline phases confined in nanocrystallites embedded in amorphous matrix. In the first stage, glassy materials were obtained by a routine melt-quenching method: pure Bi 2O 3 powders were melted in porcelain crucibles and fast-cooled down to room temperature. In the second step, the materials were appropriately heat-treated to induce formation of crystallites of β, δ or γBi 2O 3 phases confined in a glassy matrix, depending on the process conditions. It was found out that the vitrification of the initial Bi 2O 3 and the subsequent nanocrystallization were unexpectedly possible due to the presence of some Al, and Si impurities from the crucibles. Systematic DTA, XRD, optical, Raman and SEM/EDS studies were carried out to investigate the influence of the syntheses processes and allowed us to determine conditions under which the particular phases appear and remain stable down to room temperature.