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

弛豫铁电体具有优异的介电性能、压电响应和电光系数，是一种具有多种用途的功能材料。这些材料独特的宏观性质与其相当复杂的纳米结构有关，这与通过衍射分析可以检测到的平均结构有很大偏离。为了更好地理解局域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。压力主要影响原子间的短程相互作用，有助于阐明局域原子的优先有序。一大类弛豫剂是铅基复合钙钛矿。本项目旨在研究两种相同化学计量比和离子半径的化合物PbSc0.5Nb0.503和PbSc0.5Ta0.503在高p/T条件下的局域结构，以分析PbB0.5B和0.5O3型驰豫材料中的弹性张力偏爱原子团簇、压力诱导相变和重整化现象；(Ii)A掺杂和B阳离子混合PbSc0.5Nb0.503和PbSc0.5Ta0.503，以分析弹性场诱导结构转变的成分重整化。高压拉曼散射和X射线衍射实验将在单晶上进行，而不是在陶瓷上进行，以实现对结晶体中发生的局部结构现象的正确区分。将在极高的p/T下进行合成，以量身定制新型松驰剂。

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.