Pretransition state and structural transition in a deformed crystal

It is shown theoretically that a deformed crystal exhibiting structural instability can be treated as a quantum system of pseudospins. The quantum behavior of atoms becomes significant when the characteristic distance between sites of the original crystal lattice and the corresponding sites of the final phase is less thanthe amplitude of zero-point oscillations of atoms (0.1 Å) and when the area under the barrier separating the two minima of the double-well potential is less than aV2=5×10−10 eV cm.