Kunyo I. The modulated structure dynamics in strong pinning conditions in [N(CH3)4]2МеCl4 (Me = Cu, Zn, Mn), Cs2HgCl4, Cs2HgBr4 і Cs2CdBr4 crystals

The dissertation is devoted to complex study of the external factors (temperature, uniaxial pressure and electrical field along different crystal-physical directions) influence on the modulated structure dynamics in [N(CH3)4]2МеCl4 (Me = Cu, Zn, Mn), Cs2HgCl4, Cs2HgBr4 і Cs2CdBr4 crystals. The regularities of the modulated superstructure in strong pinning conditions have been state. In soliton mode of the incommensurate modulation in conditions of defects density wave existence the new multimode state of incommensurably modulated structure appears. The multiwave state is characterized by superposition of few modulation waves in one crystal-physical direction or the crystal on account of soliton structure stiffness decreasing takes domain-like structure with different periodicity of superstructure. On the basis of time behavior of the birefringence, the optical indicatrix rotation and the heat capacity it has been defined that at incommensurate superstructure changing the incommensurate wave period is not able to take equilibrium value right away but takes in series all allowed anticipant values. Therefore, the time of modulation wave formation at certain temperature relates to the creation of every anticipant modulation period value as a result of soliton motion and their interaction with defects and basis atoms of crystal lattice. At the conditions of few defect density waves existence the stochastic mode of incommensurate superstructure with chaotic phase origin realizes in the crystal.