RECONSTRUCTIVE TRANSFORMATIONS IN CRYSTAL STRUCTURES. V.P. Dmitriev, Institute of Physics, Rostov State University, Rostov on Don 344090, Russia

Most of the phase transformations occuring in crystalline objects possess a reconstructive character, with an absence of group-subgroup relarionship between the symmetries of the structures of the phases surrounding the transition. There exists however a close relationship between the preceding structures. A modern view will be presented on the theory of reconstructive phase transitions [1] which makes use of a density-wave description of the structures instead of the traditional approach based on purely symmetry considerations. The basic ideas of this modified theory of reconstructive phase transitions will be presented through the examples of compounds displaying a complex polymorphism, such as carbon, ice, silicium dioxide and cryogenic crystals.

[1]. P. Toledano and V. Dmitriev, "Reconstructive Phase Transitions" (World Scientific, Singapore, 1996).