Raman spectroscopic characterization of ZrO₂ and yttrium stabilized zirconias

Current literature on the analysis of vibrational spectra of monoclinic, tetragonal and cubic zirconias is reviewed. The selection rules based on simple factor group analysis are not obeyed for the structurally disordered tetragonal and cubic materials. The interpretation is thus not straight forward.

The spectral features of the Raman spectra do furthermore not only depend on the phase composition, but also depend on the frequency of the excitation, temperature of experiment and texture/orientation of zirconia crystallites under investigation. These effects are illustrated by Raman spectra obtained on ZrO2 and YSZ (Yttrium Stabilized Zirconias) in the range 8, 12 and 18 mol% Y2O3 and 4 mol% Yb2O3 + 4 mol% Y2O3.

The peak positions in the spectra of 8 mol% YSZ (Viking) are lowered by up to 20 cm-1 upon heating to 700 oC. Intense fluorescence/luminescence bands at 1000-1600 cm-1 were observed in clear single crystals and may tentatively be assigned to rare earth impurities (e.g. Er, Tb, Ho, Eu), although other causes are possible.

Upon cooling to liquid temperature these bands grow in intensity, ruling out their assignment as vibrational over- or combination tones. The low frequency modes at <800 cm-1, however, are reduced in intensity, only the F2g mode survives.