PECULIARITIES OF THE PIEZOOPTIC EFFECT IN INCOMMENSURATE CRYSTALS

The influence of uniaxial mechanical stress on the modulated structure which consists of a superstructure sequence is investigated in [N(CH3 )(4)](2)MeCl(4) (Me = Cu, Fe, Zn) crystals. The peculiarities of the e ffective piezooptic coefficients pi(ij)(0) within the incommensurate p hase of these crystals are studied by Senarmont's method. The influenc e of uniaxial mechanical stress disturbs the conditions of modulated s tructure interaction with defects what leads to the appearance of the widening of metastable states and to anomalies in the physical charact eristics. It causes the change of the region of the localization of th e incommensurability wave vector k on the commensurate values of highe r order.