TOPICAL SEMINAR on structure and dynamics of crystals

04-16-2024 15:00 Conference hall (bldg. 42, 3rd floor)

Trigger transitions are structural transitions in which the structural distortion is the sum of two distortions corresponding to different irreducible concepts and the critical stiffness behavior (soft mode) is observed for only one of them. Previously, such transitions were identified for ferroelectrics. New experiments have revealed another type of trigger transitions - trigger incommensurate transitions, where the occurrence of an incommensurate modulation wave is caused by a soft mode with respect to another order parameter - antiphase tilts of oxygen octahedral groups. Such transitions were detected experimentally in the antiferroelectric PbHfO3 and were also studied in a wider group of materials and under changing external conditions, such as hydrostatic pressure and positioning the material in an epitaxial heterostructure. Using pressure and chemical substitutions, it is possible to separate the trigger transition into two separate transitions, thus developing an intermediate phase in which the disproportionate soft mode is activated. The experiments were carried out using diffraction, diffuse and inelastic scattering of synchrotron radiation and various approaches to simulation of phenomena were used. Qualitatively new phase transitions have been revealed in the epitaxial structures of antiferroelectrics. The results may be useful for the development of new approaches to the use of antiferroelectrics in the field of electrical energy storage and non-volatile data storage.