Raman spectroscopic studies on sodium metavanadate

Abstract

Sodium metavanadate (NaVO₃) has been reported earlier to exhibit ferroelectric behaviour below 380°C, but unlike many other known ferroelectrics it does not show a very strong dielectric anomaly, indicating that the structural change during the ferroelectric phase transition may be only a slight modification of the paraelectric phase. This is in conformity with the X-ray data at room temperature, which could be refined to the same R value either in space group C2/c or Cc. Further, it is known that NaVO₃ occurs also in another polymorphic modification (β-form), the structure of which has not been established. Raman spectroscopic studies of single crystals of the α-form of NaVO₃ have been carried out and a crystalline powder of the β-form has been made. The Raman spectra have been interpreted in terms of the linear VO₃⁻ chains formed by VO₄ tetrahedra sharing two corners with each other. The temperature variation of the intensity and width of the Raman lines through the phase transition has been measured and the observed LO-TO splitting in the room temperature phase confirm the Ce ferroelectric space group.