UV Raman spectroscopic study on the phase transformation of ZrO2, Y2O3-ZrO2 and SO42-/ZrO2

The phase evolution of zirconia (ZrO2), sulfated zirconia (SO42-/ZrO2) and yttrium oxide incorporated zirconia (Y2O3-ZrO2) from the tetrahedral phase to the monoclinic phase was studied using UV Raman spectroscopy, visible Raman spectroscopy and x-ray diffraction (XRD). It is clearly observed that there are discrepancies between the results from the UV Raman spectra, visible Raman spectra and XRD patterns. The phase change from tetragonal to monoclinic is always earlier or at lower calcination temperatures as observed by UV Raman spectroscopy than by visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD supply the information mainly from the bulk. The inconsistency in the results from the three techniques suggests that the phase transformation of zirconia starts from its surface region and then gradually develops into its bulk. For SO42-/ZrO2 and Y2O3-ZrO2, the transformation from the tetragonal to the monoclinic phase is significantly retarded owing to the presence of the sulfated groups and the yttrium oxide. Particularly, the tetragonal phase of Y2O3-ZrO2 can be maintained up to 800degreesC although its phase at the surface region changed into monoclinic at 500degreesC. Copyright (C) 2002 John Wiley Sons, Ltd