Raman spectra and vibrational analysis of nanometric tetragonal zirconia under high pressure

Raman spectra of nanometric tetragonal zirconia have been recorded under hi gh pressure up to 31 GPa. The two lowest frequency modes exhibit an unusual over-damped soft mode behaviour upon increasing pressure. The non-crossove r of these modes is the indication that they belong to the same symmetry an d this lead us to reconsider the previous normal mode assignment. A new ass ignment of Raman active mode is deduced from normal mode calculations based on the linear chain model. The continuous loss of intensity and the soften ing of the Eg low frequency mode are likely associated with a phase transit ion which could take place around 38 GPa. The discussion of an evolution of the compound towards a possibly distorted fluorite-like structure at high pressure is based on the reduction of the number of Raman bands and on the decrease of the anisotropy of the microscopic compressibility coefficients estimated from the pressure evolution of force constants. (C) 2000 Elsevier Science Ltd. All rights reserved.