Characterization and Stabilization of Metastable Tetragonal ZrO ₂

Fine single‐domain and polydomain particles of tetragonal ZrO 2 were prepared by hydrothermal and heat treatment of ZrO 2 · n H 2 O. The particles were characterized by X‐ray diffraction, electron microscopy, NMR, mass spectrometry, and ir spectroscopy. The main impurity in the samples was 1 to 2 wt% OH − ions, most of which were concentrated on the particle surfaces or at domain boundaries; some were also distributed in the lattice. Fine single‐domain tetragonal particles were strain‐free, but polydomain particles had large strains. The single‐domain tetragonal particles were transformed much more easily than the polydomain particles by mechanical treatment. The stablization of metastable tetragonal ZrO 2 cannot be explained adequately by the surface‐energy theory. An explanation based on the concept of a martensitic transformation may be more reasonable.