The phase Bi20 2Te exists in the pseudobinary system Bi203/Bi2Te3. The thermal behaviour of Bi2Ö2Te was determined by DTA and X-ray analysis: The phase exists up to 620 °C and decomposes into the solid phases Bi12TeO20, Bi10Te2O 19 [1] and liquid BiTe. The relations of the phase coexistences in the pseudobinary system and in the ternary area Bi20 3/Te02/Bi2Te3/Te were investigated by solid state reactions, chemical transport reactions, and by total pressure measurements.

Six phases exist in the binary system iron-germanium Fe3Ge, β, η, Fe6Ge5, FeGe and FeGe2. All phases could be prepared by chemical transport with iodine as transport agent in the temperature range between T1 (600 °C) and T2 (950 °C). Two phase diagrams have been known in the literature from specific experiments of chemical vapour transport. It is now possible to decide which phase diagram is the most valid description.

Chemical Vapour Transport, Calculation of CTR, Thermodynamic Data Five phases exist in the system Co-Si: Co3Si, aand /?-Co2Si, CoSi and CoSi2. The phases a-Co2Si and CoSi could be prepared by chemical transport with iodine as transport agent in the temperature range between Ti (700 °C) and T2 (900 °C). In a attempted systematic clarification of the chemical transport reactions of all phases in the system, the effective transport equilibria were determined. Thermodynamic data show satisfactory agreement bet ween calculation and experiment.

Five phases exist in the system Fe-Si: Fe3Si, Fe2Si, Fe5Si3, FeSi, α-and β-FeSi2. All phases could be prepared by chemical transport with iodine as transport agent in the temperature range between T1 (700 °C) and T2 (1030 °C). In a attempted systematic clarification of the chemical transport reactions of all phases in the system, the effective transport equilibria were determined. Thermodynamic calculations show satisfactory agreement between calcula­tion and experiment.

Chemical Transport Reactions, Total Pressure Measurement, Calculation o f CTR, Thermodynamic DataGeTe, SnTe, and PbTe have been prepared by chemical transport reactions with iodine as transport agent in the temperature range between T2 (800 -700 °C) and T , (700 -500 °C). The effective transport equilibria were determineted. Total pressure measurements in the system Ge-Te-I give the coexistence equlibria for condensed phases, and also for the gasphase equilibra. GeTe4 exists only as a metastable phase at lower temperatures and decom poses near 260 °C in GeTe and Te.Thermodynamic calculations show satisfactory agreement between calculation and experi ment.