Monoclinic to tetragonal semireconstructive phase transition of zirconia

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 [010](m)parallel to [001](t) and (100)(m)parallel to (110)(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.