New quenched-in fluorite-type materials in the Bi2O3–La2O3–PbO system: Synthesis and complex phase behaviour up to 750 °C

New quenched-in fluorite-type materials with composition (BiO1.5)0.94−x(LaO1.5)0.06(PbO)x, x = 0.02, 0.03, 0.04 and 0.05, were synthesised by solid state reaction. The new materials undergo a number of phase transformations during heating between room temperature and 750 °C, as indicated by differential thermal analysis. Variable temperature X-ray diffraction performed on the material (BiO1.5)0.92(LaO1.5)0.06(PbO)0.02 revealed that the quenched-in fcc fluorite-type material first undergoes a transformation to a β-Bi2O3-type tetragonal phase around 400 °C. In the range 450–700 °C, α-Bi2O3-type monoclinic, Bi12PbO19-type bcc and β1/β2-type rhombohedral phases, and what appeared to be a ɛ-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 °C.