Investigations on the system BiOCl/SeO2

The section BiOCl/SeO2 was shown to be quasibinary one and include only one intermediate phase BiOCl . SeO2 = BiSeO3Cl. The phase barogram and the pha se diagram were determined by total pressure measurements and DTA. BiSeO3Cl shows on heating two transitions in crystal phase, (alpha --> beta) at 400 +/- 2 degreesC and (beta --> gamma) at 410 +/- 3 degreesC. The compound me lts peritectically at 417 +/- 3 degreesC. The experiments on sublimation of BiSeO3Cl in the temperature gradient and chemical vapour transport with Se O2 allowed to make the conclusion on the existence of BiSeO3Cl molecules in the vapour. Some standard thermodynamic data were determined by solution c alorimetry and evaluated from the vapour pressure and chemical vapour trans port rate data.