Mesoscopic-scale transformation processes in Bi-based perovskite-type ferroelectric solid solutions

我们的现代生活是不可想象的，没有铁电体：材料与自发极化开关下的外部电场，表现出大的介电常数以及强大的压电，热电和光电响应。大多数先进的铁电体是钙钛矿型（ABO 3）固溶体，具有准同型相界（MPB）：一个临界组成x，铁电长程有序的对称性发生变化，性质被强烈放大。众所周知，在MPB附近存在丰富的纳米级结构不均匀性。然而，尽管在过去的几十年里，建立了一个广义的组成-结构-性能关系的原子模型的巨大努力，化学诱导的结构不稳定性和MPB附近的宏观性能增强的驱动机制仍然没有得到澄清。寻找环境友好的铅减少或无铅的替代品的著名的PbZrxTi 1-xO 3的追求导致了越来越多的兴趣，铋基钙钛矿型铁电体。利用拉曼光谱和总中子散射对新型Bi基固溶体中局部结构和原子动力学的成分依赖性进行了深入研究，这是MI 1127/8-1项目的主题。到目前为止所获得的结果表明，在MPB的较大的压电响应是由于A-和B-位点阳离子振动之间的同步增加。在特定的ABO 3型固溶体的上级压电性能的结果从绝对平坦的局部电位的所有铁电活性阳离子保持相对较高的极性位移在MPB。本延续项目的主要目标是完成（1-x）PbTiO 3-xBiMeO 3固溶体（Me = Mg 0. 5 Ti 0. 5，Ni 0. 5 Ti 0. 5，Ni 0. 5 Zr 0. 5）介观尺度相变过程的比较研究。对于每个系列，将通过拉曼光谱和成对分布函数分析，并在宽温度范围内（包括远高于居里温度的高温）进行反向蒙特卡罗模拟，对MPB中的四种选定化合物进行分析。结果有望澄清的原子驱动力形成的高度无序的结构状态在MPB，从我们的分析显示在室温下。对重归一化现象的比较分析将大大提高我们对居里温度和压电系数依赖于掺杂剂类型的微观起源的理解，从而可能对设计新型功能材料的策略产生关键影响。

Our modern life is unthinkable without ferroelectrics:materials with spontaneous polarization switchable under an external electric field, which exhibit large dielectric permittivity as well as strong piezoelectric, pyroelectric and optoelectric responses. The majority of advanced ferroelectrics are perovskite-type (ABO3) solid solutions possessing a morphotropic phase boundary (MPB): a critical composition x at which the symmetry of the ferroelectric long-range order changes and the properties are strongly amplified. It is well known that in the vicinity of MPB there are abundant nanoscale structural inhomogeneities. However, although the enormous efforts over the past decades to establish a generalized atomistic model of the relation composition - structure – properties, the driving mechanism of chemically induced structural instability and enhanced macroproperties near MPB is still not clarified. The quest to find environmentally friendly Pb-reduced or Pb-free alternatives of the famous PbZrxTi1-xO3 has led to an increasing interest in Bi-based perovskite-type ferroelectrics. A thorough study of the composition dependence of the local structure and atomic dynamics in novel Bibased solid solutions using Raman spectroscopy and total neutron scattering was the subject of project MI 1127/8-1. The results obtained so far reveal that the larger piezoelectric response at the MPB is due to the increased synchronization between the A- and B-site cation vibrations. The superior piezoelectric properties in specific ABO3-type solid solutions result from to the absolute flattening of the local potentials for all ferroelectrically active cations preserving relatively high polar displacements at MPB. The major goal of this continuation project is to complete the comparative study on the mesoscopic-scale transformation processes in (1-x)PbTiO3-xBiMeO3 solid solutions with Me = Mg0.5Ti0.5, Ni0.5Ti0.5, Ni0.5Zr0.5. For each series four selected compounds across the MPB are going to be analyzed by Raman spectroscopy and pair-distribution-function analyses complemented by reverse Monte Carlo simulations in a wide temperature range, including high temperatures well above the Curie temperature. The results are expected to clarify the atomistic driving forces of formation of highly disordered structural state at the MPB, as revealed from our analyses at room temperature. The comparative analyses of the renomalization phenomena will considerably improve our understanding of the microscopic origin of the dependence of the Curie temperature and piezoelectric coefficients on the type of the dopant and thus, may have critical effect on the strategy of designing novel functional materials.