High pressure Raman studies of β-NaVO3

Abstract In an earlier study, the α-phase, which is one of the stable forms of NaVO 3 under ambient conditions, has been shown to undergo a crystalline-amorphous phase transition at c . 60kbar [Shen el at., J. Phys. Chem. Solids 55 , 665 (1994)]. In the amorphous phase, the chains consisting of corner-sharing VO 4 tetrahedra break up into individual VO 3 pyramids. We now report on the high pressure study of the β-form, for which three phase transitions have been found. The first transition at 14 kbar is of first order and involves major structural changes. The second at about 44 kbar is second order and only subtle spectral changes are seen. The third is at 80 kbar and the sample may be partially disordered in this phase. Most importantly, despite the fact that both the α- and β-forms are stable phases of NaVO 3 under ambient conditions, their difference persists to very high pressure, and no amorphous phase is observed up to 166 kbar in β -NaVO 3 .