Application of In-situ Raman Spectroscopy on NaVO₂F₂ Phase Transformation Study

The NaVO₂F₂ compound was synthesized by hydrothermal method. The crystal structure of NaVO₂F₂ was analyzed by X-ray diffraction. In-situ Raman spectra of NaVO₂F₂ during the heating from 73 K to 573 K was obtained by Raman spectroscopy. The changes of characteristic peaks with temperature was analyzed and the phase transformation behavior was obtained. The results show that the obtained NaVO₂F₂ crystal was monoclinic at room temperature with space group P2₁/c. During the heating process, the low-temperature first-order phase transformation, transformation from low-temperature phase to P2₁/c phase and transformation from P2₁/c phase to P2₁/m phase occurred at the temperature point of 93, 233, 453 K, respectively. The results were in good agreement with those obtained by non-in-situ testing method, indicating that the in-situ Raman spectroscopy could be used to study the phase transformation behavior of NaVO₂F₂.