High-temperature Raman spectroscopic study of vanadoborate Na_3VO_2B_6O_(11)

Raman spectra of a vanadoborate (Na₃VO₂B₆O₁₁) crystal from room temperature up to the melting point have been recorded. The main internal vibrational modes of the crystal have been assigned. It was found that all the Raman bands exhibit decreases in frequency and the widths of the Raman bands increase with the increase of temperature. However, no phase transition was observed under 525 ℃. The micro-structure of its melt was studied by quantum chemistry ab initio calculation. The continuous three-dimensional network of the crystal collapsed and transformed into VO₄ and VBO₆ clusters during the melting process with an isomerization reaction from four-coordinated boron to a three-coordinated species.