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Structural Disorder and Coherence across the Phase Transitions of Lead-Free Piezoelectric Bi0.5K0.5TiO3
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-03-30 00:00:00 , DOI: 10.1021/acs.chemmater.7b05278 Bo Jiang 1 , Trygve M. Raeder 1 , De-Ye Lin 2 , Tor Grande 1 , Sverre M. Selbach 1
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-03-30 00:00:00 , DOI: 10.1021/acs.chemmater.7b05278 Bo Jiang 1 , Trygve M. Raeder 1 , De-Ye Lin 2 , Tor Grande 1 , Sverre M. Selbach 1
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Relaxor ferroelectrics exhibit superior properties for converting mechanical energy into electrical energy, and vice versa, but the structural disorder hampers an understanding of structure–property relationships and impedes rational design of new, lead-free materials. Bi0.5K0.5TiO3 (BKT) is a prototypical lead-free relaxor ferroelectric, but the microscopic origins of polarization, nature of the ferroelectric transition (TC), and structural changes across the tetragonal to pseudocubic transition (T2) are poorly understood. Here the local and intermediate structure of BKT is studied from room temperature to above TC by pair distribution functions (PDFs) from synchrotron X-ray total scattering experiments and complemented by ab initio molecular dynamics (AIMD) simulations. The local structure varies smoothly across T2 as well as TC, in contrast to the abrupt changes at TC inferred from conventional diffraction. Ferroelectric distortions are larger on the local scale than in the average structure, with polar Ti4+ displacements prevailing above TC. We find that local polar regions partly cancel each other below TC, while completely averaging out above, implying that BKT goes through a transition from partial to complete disorder across TC.
中文翻译：
无铅压电Bi 0.5 K 0.5 TiO 3相变中的结构无序和相干性
弛张铁电体具有将机械能转换为电能的优良特性，反之亦然，但是结构紊乱妨碍了对结构与特性关系的理解，并阻碍了新的无铅材料的合理设计。Bi 0.5 K 0.5 TiO 3（BKT）是一种典型的无铅弛豫铁电体，但是其极化的微观起源，铁电跃迁的性质（T C）和从四方到伪立方跃迁的结构变化（T 2）都很差。了解。在此研究了从室温到高于T C的BKT的局部和中间结构通过同步加速器X射线总散射实验中的对分布函数（PDF）进行计算，并辅以从头算分子动力学（AIMD）模拟。与传统衍射推断的T C处的突变相比，T 2和T C处的局部结构平滑变化。铁电失真是在本地规模比平均结构较大，与极性的Ti 4+位移盛行以上Ť Ç。我们发现局部极区在T C以下相互抵消，而在上面将其完全取平均值，则意味着BKT在T C上经历了从部分无序到完全无序的过渡。
更新日期：2018-03-30
中文翻译：
无铅压电Bi 0.5 K 0.5 TiO 3相变中的结构无序和相干性
弛张铁电体具有将机械能转换为电能的优良特性，反之亦然，但是结构紊乱妨碍了对结构与特性关系的理解，并阻碍了新的无铅材料的合理设计。Bi 0.5 K 0.5 TiO 3（BKT）是一种典型的无铅弛豫铁电体，但是其极化的微观起源，铁电跃迁的性质（T C）和从四方到伪立方跃迁的结构变化（T 2）都很差。了解。在此研究了从室温到高于T C的BKT的局部和中间结构通过同步加速器X射线总散射实验中的对分布函数（PDF）进行计算，并辅以从头算分子动力学（AIMD）模拟。与传统衍射推断的T C处的突变相比，T 2和T C处的局部结构平滑变化。铁电失真是在本地规模比平均结构较大，与极性的Ti 4+位移盛行以上Ť Ç。我们发现局部极区在T C以下相互抵消，而在上面将其完全取平均值，则意味着BKT在T C上经历了从部分无序到完全无序的过渡。
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