Order-disorder transition of the metal vacancies in the vanadium-sulfur system. I. An experimental study
The phase diagram of the VS-VS 2 system was studied by high-temperature DTA and X-ray measurements. As a result, it has been confirmed that the vacancy-ordered V 3S 4-type structure transforms into the CdI 2-type structure at Tc 1 while the vacancy-ordered V 5S 8-type structure shows successive transformations on heating; V 5S 8 type limit→T c2V3S4 type limit→T c1Cdl2 type. The mechanisms of the phase transitions are discussed from the viewpoint of structural relationships. The phase diagram of the VS-VS 2 system is constructed in the temperature range up to 1200°C. In the VSe system similar results to those in the VS system have been obtained. The VSSe system has also been studied and the result supports the above-mentioned results on the VS and VSe systems.