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 degrees 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 beta-Bi2O3-type tetragonal phase around 400 degrees C. In the range 450-700 degrees C, alpha-Bi2O3-type monoclinic, Bi12PbO19-type bcc and beta(1)/beta(2)-type rhombohedral phases, and what appeared to be a epsilon-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.