Аннотация:High-temperature transformation of β-PtBi2, a synthetic analogue of insizwaite, was studied under oxidizing conditions (on air). The behavior of the sample upon heating up to 660°C and cooling was studied by differential thermal analysis (DTA) and high-temperature X-ray powder diffraction. It was shown that polymorphic transitions of β-PtBi2 into high-temperature γ- and δ-polymorphs do not occur under thermal treatment in the oxidizing conditions (on air). The DTA curve shows two exothermic peaks at 318 and 620°C. The total weight change in the temperature range studied is +10.5%. No thermal reactions or weight changes were recorded upon cooling of the sample. According to the high-temperature diffraction experiment in situ, the decomposition of the synthesized phase into Pt and Bi was recorded with their subsequent oxidation to bismuth oxide Bi2O3 with the bismite-type structure and double platinum and bismuth oxide with the pyrochlore-type structure Bi2Pt2O7. The study by electron microprobe analysis showed that the grains of the transformed insizwaite are a finely dispersed mixture of two oxides.
