Thermoanalytical study of the polymorphism and melting behavior of Cu2V2O7

We have developed a procedure for the synthesis of phase-pure alpha- and beta-Cu2V2O7. Thermal analysis and X-ray diffraction demonstrate that the beta-phase (monoclinic structure) exists at low temperatures (stability range 25-610A degrees C), while alpha-Cu2V2O7 (orthorhombic structure) is stable in the range 610-704A degrees C. The alpha-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase gamma-Cu2V2O7, which forms between 704 and 716A degrees C, has the highest rate in the range 770-785A degrees S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9A degrees C) is attributable to the crystallization of the peritectic melt, one (620.1A degrees C) is due to the gamma -> alpha -> beta phase transformations of Cu2V2O7, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing alpha- and beta-Cu2V2O7, CuVO3, and other compounds.