Investigation of phase transition in self-flux grown VO2 single crystals

초록

We report the growth and phase transition of VO2 single crystals. Millimeter-sized VO2 single crystals were obtained by a self-flux method, in which the molten phase of V2O5 at 1000 degrees C was slowly cooled to room temperature at a rate of 5 degrees C/h. Rietveld analysis of X-ray powder diffraction shows a low-temperature monoclinic structure with the V-V dimer spacings of 2.57 angstrom and 3.20 angstrom and a high-temperature rutile structure with the V-V spacing of 2.85 angstrom. Raman scattering measurement suggests that the VO2 single crystal is highly stoichiometric with negligible oxygen deficiency. Electrical resistivity, magnetic susceptibility, specific heat, and heat flow measurements show drastic changes during heating (similar to 338 K) and cooling (similar to 334 K) with a narrow temperature range (similar to 1 K). The low-temperature insulating phase with negligible magnetic susceptibility changes to a high-temperature metallic phase with Pauli paramagnetic susceptibility. The enthalpy change during the phase transition was estimated to be similar to 87 J/g by specific heat and differential calorimetry measurements. This work provides useful quantitative information for the phase transition of VO2 single crystals.

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