Vanadium oxides V2O5 and NaV2O5 under high pressures: Structural, vibrational, and electronic properties

The effect of pressure on the physical properties of V2O5 and NaV2O5 has be en studied by high-resolution angle-dispersive X-ray powder diffraction, Ra man spectroscopy, and optical reflectivity measurements. We present a compa rative study of the structural, vibrational and electronic properties of bo th compounds under pressure. The compression of V2O5 and NaV2O5 is highly a nisotropic with the stacking directions of the layered structures being the soft axes. A structural phase transition to a three-dimensionally linked s tructure occurs at similar to7 GPa in V2O5 as compared to similar to 25 GPa in NaV2O5. This indicates that intercalation of Na results in a higher sta bility of the V2O5 layers under pressure. Ln either case the V coordination changes from 5- to 6-fold. Substantial red shifts of the optical excitatio n spectra and changes of the vibrational properties accompany the phase tra nsitions. (C) 2001 Elsevier Science B.V. hll rights reserved.