Vibrational properties of NaV2O5 under high pressure studied by Raman spectroscopy

Vibrational properties of NaV2O5 under pressures up to 33 GPa have been stu died by Raman spectroscopy (T = 300 K). Up to 10 Cpa the phonon frequencies exhibit pronounced nonlinear pressure dependences which can be correlated with distinct structural changes. Increasing layer interaction causes a maj or softening of the V=O1 out-of-plane stretching mode. The phonon-electroni c-excitation coupled mode at 453 cm(-1) was found to be particularly sensit ive to structural changes. A phase transition from the layered towards a th ree-dimensionally linked structure starts near 25 Gpa. The transition press ure is significantly reduced under non-hydrostatic pressure conditions. The intercalation of Na stabilizes the low-pressure phase of NaV2O5 in compari son to V2O5. (C) 1999 Elsevier Science Ltd. All rights reserved.