Solid-state reaction pathways of Sillenite-phase formation studied by high-temperature X-ray diffractometry and differential thermal analysis

This paper reports on the use of high-temperature X-ray diffractometry, in conjunction with differential thermal analysis, to study the solid-state reactions and phase transformations involved in and leading to the synthesis of various (bismuth oxide-based) Sillenite-type compounds. These, which have γ-body centered cubic (bcc) structures related to γ-Bi2O3, are generally represented by the formula Bi12MO20; here, the second cation M=Ge, Si, Ti, Zn, Al, as well as the two-cation combination {Si0.5Ge0.5}. In each case, using the two techniques, measurements were performed on starting powder-mixtures of bismuth and cation M oxides, formulated with desired proportions to favor the Sillenite (γ-)phase formation. Henceforth, the proceeding of solid-phase reactions and occurring of phase transitions, with rising temperature, were monitored and elucidated by the evolution of the X-ray diffractometry patterns and the appearance of thermal events in the differential thermal analysis curve, as both sets of results were also correlated.