New quenched-in fluorite-type materials in the Bi_2O)3-La)2O)3-PbO system: Synthesis and complex phase behaviour up to 750 ℃

摘要

New quenched-in fluorite-type materials with composition (BiO_(1.5))_(0.94-x)(LaO_(1.5))_(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 (BiO_(1.5)_(0.92)(LaO_(1.5))_(0.06)(PbO)_(0.02) revealed that the quenched-in/cc fluorite-type material first undergoes a transformation to a ss-Bi_2O_3-type tetragonal phase around 400 C In the range 450-700 C, α-Bi_2O)3-type monoclinic, Bi_(12)PbO_(19)-type bcc and ss_1/ss_2-type rhombohedral phases, and what appeared to be a s-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 ℃.