Department of Materials Science, Indian Association for the Cultivation of Science^* Department of Physics, Vivekananda Mahavidyalaya, Haripal, Hooghly 712405, India^**
○Apurba Kanti Deb^* Partha Chatterjee^** Siba Prasad Sen Gupta^*

A detailed study on the phase stability of ZrO₂ in the tetragonal phase at room temperature and near its transformation temperature and its structural and microstructural features in the alpha-Al₂O₃ matrix has been conducted using X-ray structural and microstructural refinement using Rietveld method, TEM, FTIR and Raman spectroscopy. It is observed that the tetragonal ZrO₂ is stabilized in an alumina matrix up to a wt. fraction of ~ 0.58. The crystallite size (54 nm), obtained from the X-ray diffraction analysis, is in accordance with TEM studies (65 nm). The size value is well above the critical size limit as reported in the literature. It is found that microstrains play a role in the stabilization process. A detailed structural analysis reveals that the tetragonal distortion for t-ZrO₂ in the composites is similar to that of pure t-ZrO₂, no indication of Al₂O₃ -ZrO₂ solid solution formation from X-ray and FTIR study was obtained. The Rietveld refinement discloses oxygen deficiency in t-ZrO₂. Thus in conclusion for size-stabilized t-ZrO₂ the critical size limit is proposed to be ~ 54 nm and that the stabilization process is also influenced by other factors such as oxygen vacancy, microstrain.