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

弛豫铁电体是一种具有优异介电性能、压电响应和电光系数的功能材料，具有广泛的应用前景。这些材料独特的宏观性质与其相当复杂的纳米级结构有关，该结构与衍射分析可检测到的平均结构有很大差异。为了更好地理解局部结构现象和弛豫行为之间的相互作用，我们将在原位p/T条件下应用衍射和声子光谱方法。压力将有助于阐明优先的局部原子有序，因为它主要影响短程原子间的相互作用。主要的弛豫剂是铅基复合钙钛矿。本项目旨在研究（i）具有相同化学计量和离子半径的两种化合物PbSc0.5Nb0.5O3和PbSc0.5Ta0.5O3在高p/T条件下的局部结构，以分析Pb B B 0.5O3型弛豫器中的原子团簇、压力诱导相变和重整化现象。- 阳离子混合PbSc_（0.5）Nb_（0.5）O_3和PbSc_（0.5）Ta_（0.5）O_3的弹性场诱导结构转变的组分重整化。高压拉曼散射和X射线衍射实验将在单晶上而不是在陶瓷上进行，以实现对晶体块体中发生的局部结构现象的正确区分。将在极高p/T下进行合成以定制新型弛豫剂。

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.