The article presents the results of a study of the heat capacity of V1-XFeXO2, temperatures of phase transformations in the semiconductor phase have been determined. The phase transition diagram of the V1-XFeXO2 system is presented. Values of the change in the entropy of phase transformations for V1-XFeXO2 materials are determined. It was determined that the values of the change in the entropy of the metal-semiconductor phase transition decrease with iron concentration increasing. The results of differential thermal analysis, temperature dependences of electrical resistivity, magnetic susceptibility, and thermoelectric coefficient are presented for the FeV2O6 compound. It was determined that the FeV2O6 compound is a semiconductor in the temperature range from 100 К up to 400 К.
The article presents the research results of the thermal cycling influence on the ratio of the ultimate composition, chemical state and electrical resistance of VO2±Y system materials. It is established that for all VO2±Y system materials a phase transition semiconductor-metal (PTSM) is observed at temperature of ∼ 340 K, accompanied by a sharp change in electrical resistance both before and after thermal cycling. Despite the fact that PTMD retained after thermal cycling, the resistivity jump Δln(R/R0) at PTMD for all test materials decreases, the transition temperature becomes more diffused. It is shown that after a series of 30 thermal cycles, the ratio of the surface ultimate composition of all the materials under study changes to a decrease in the oxygen content. Minimal changes in properties as a result of thermal cycling are observed in vanadium dioxide of stoichiometric composition. According to the results of XPS spectra, it was determined that V4+ oxide predominates in the surface layer of VO2 samples, both before and after thermal cycling, and there are also small inclusions of V5+ oxide.
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