High pressure-induced structural transformations in lead-based perovskite type relaxor ferroelectrics

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Relaxor ferroelectrics are functional materials with multiple applications due to their extraordinary dielectric properties, piezoelectric response and electrooptical coefficients. The unique macroproperties of these materials are related to their rather complex nanoscale structure, which deviates substantially from the average structure detectable by diffraction analysis. In order to better understand the interplay between the local structural phenomena and relaxor behaviour we are going to apply diffraction and phonon spectroscopic methods under in situ p/T conditions. Pressure will help to elucidate the preferential local atomic ordering, since it affects mainly the short-range interatomic interactions. A major group of relaxors are lead-based complex perovskites. This project aims to study (i) the local structure of two compounds with equal stoichiometry and ionic radii, PbSc0.5Nb0.5O3 and PbSc0.5Ta0.5O3, under high p/T conditions in order to analyse elastic tension-favourite atomic clustering, pressure-induced phase transformations and renormalization phenomena in relaxors of type PbB¿0.5B¿0.5O3; (ii) A-doped and B¿-cation mixed PbSc0.5Nb0.5O3 and PbSc0.5Ta0.5O3 in order to analyse the compositional renormalization of elastic field-induced structural transformations. The high-pressure Raman scattering and X-ray diffraction experiments will be performed on single crystals, not on ceramics, to achieve correct differentiation of the local structural phenomena occurring in the crystalline bulk. Syntheses under extremely high p/T will be performed to tailor novel relaxors.