Accurate data, obtained by neutron diffraction, have been used to monitor the first-order reconstructive monoclinic↔tetragonal phase transition as a function of the temperature both during heating and cooling. Data analysis supports an orientational relationship $\left[010{]}_m\Vert \right[001{]}_t$ and ${\mathrm{}\left(100\right)\mathrm{}}_m\Vert {\mathrm{}\left(110\right)\mathrm{}}_t$ between the tetragonal and the monoclinic phases. The analysis of the oxygen atoms evolution in the tetragonal phase supports a displacive mechanism for the monoclinic↔tetragonal phase transition. Based on these data, a microscopic model is proposed explaining the unusual behavior of zirconia.

• Received 26 June 2002

DOI:https://doi.org/10.1103/PhysRevB.67.064111