Physico-chemical properties of V_1-XFe_X O₂ and FeV₂O₆

Abstract

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.

Precise Characterization of the Rich Structural Landscape Induced by Pressure in Multifunctional FeVO4

“…Indeed, phase transitions are known to produce an entropy increase in iron vanadate, which would probably produce a decrease of the free energy favoring the transition to FeVO 4 -II′ . On the other hand, the entropy increase observed in the phase transitions suggests a possible diffusion of V and Fe, which is generally favored by temperature but can happen with pressure also, in particular in the case of a first-order reconstructive transition. Making calculations at finite temperatures to include the entropy is computationally demanding because it is required to determine the complete phonon dispersion, which is beyond the scope of this work.…”

“…The differences in the enthalpies between FeVO 4 -I′ and FeVO 4 -II′ (∼0.1 eV) are comparable with the thermal energy at 300 K, which suggests that the FeVO 4 -I′-to-FeVO 4 -II′ transition could be driven by phonon entropy effects or atomic diffusion, which were not included in the calculations . Indeed, phase transitions are known to produce an entropy increase in iron vanadate, which would probably produce a decrease of the free energy favoring the transition to FeVO 4 -II′ . On the other hand, the entropy increase observed in the phase transitions suggests a possible diffusion of V and Fe, which is generally favored by temperature but can happen with pressure also, in particular in the case of a first-order reconstructive transition.…”