Evidence for oxygen nonstoichiometry in a stabilized Bi–Ca–Pb–O fluorite-type phase

Abstract

Investigations performed on quenched samples of the Bi–Ca–Pb–O fluorite-type phase using thermogravimetry (TG), X-ray diffraction (XRD) and chemical analysis have unambiguously provided evidence for the formation of Bi⁵⁺. When samples were annealed in air below the decomposition temperature of the fluorite phase (ca. 420 °C), the Bi⁵⁺/(Bi³⁺+ Bi⁵⁺) ratio increased progressively versus temperature up to a maximum value, being a function of the composition, and the cubic-cell parameter decreased. This decrease has been interpreted as due to the joint effects of Bi³⁺→Bi⁵⁺ partial oxidation and oxygen ordering.