Bond-switching mechanism for the zircon-scheelite phase transition

The stress-induced zircon-scheelite phase transition is theoretically studied by means of ab initio and shell-model calculations. It is shown that this phase transition may originate from shear elastic strains which bring together the structures of both phases and draw them unstable against the SiO4- tetrahedron rotations necessary for direct and inverse conversions. As a result, a structural catastrophe occurs within the ZrO8 polyhedrons: part of the Zr-O bonds disrupts and new ones form. Such a bond switching is crucial for the first-order reconstructive character of the transition which, according to this study, would proceed via the D-4h(19)-D-2h(24)-C-2h(6)-C-4h(6) symmetry group succession.