Solid-State NMR Characterization of the Local Structure of Lead-Free Relaxor Ferroelectrics

无铅弛豫铁电体局部结构的固态核磁共振表征

• 批准号: 397608312
• 负责人: Professor Dr. Gerd Buntkowsky
• 金额: --
• 依托单位: Fachgebiet Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/397608312?language=en
• 关键词: Solid; State; NMR; Characterization; Local

Sodium-bismuth titanate and its solid-solutions with barium (100-x)(Na1/2,Bi1/2)TiO3 (x)BaTiO3 (NBT xBT) stand out as a promising and environmentally friendly alternative to lead-based piezoelectric ceramics. These intrinsically inhomogeneous materials exhibit structural distortions with small magnitude and short coherence length, which pose a challenge to their characterization with conventional methods that are sensitive only to the average structure. As a consequence, key aspects of the structure-property relations in these materials are still unclear, as for example the role of chemical modifications, the nature of phase transitions (either temperature or electric field-induced) and the occurrence of a relaxor ferroelectric state. In this project, we employ solid-state nuclear magnetic resonance (ssNMR) spectroscopy in order to face the challenges posed by this class of materials and to learn about their structure at the local scale. This will be achieved by the analysis of static, one-dimensional MAS and in particular two-dimensional 3QMAS NMR spectra, which enable a description of the local structure in terms of the nuclear interactions present for 23Na and other NMR-active nuclei available. The investigation of the temperature dependence of relevant NMR parameters should shed light on the changes occurring to the local structure of the NBT-xBT compositions, both unpoled and poled, throughout the temperature range from below the depolarization temperature (Td) over the ferroelectric-to-relaxor transition temperature (TF R) and the dielectric permittivity’s maximum temperature (Tm) and above. Dynamical aspects of the local structure will be investigated both in the ferroelectric and relaxor states by the investigation of NMR relaxation times, aiming at the identification of the nature of local structural fluctuations present in these materials. The focus of the first application period was the characterization of the dependence of the local structure and electric polarization of (Na1/2,Bi1/2)TiO3 solid-solutions with barium titanate (NBT xBT, 0≤x≤15) with solid-state NMR. In the second application period we first want to (a) finish our studies on the nature of the apparently cubic phase in the NBT xBT system. For this we will (a) solve the problem of the missing side-band intensity in the MAS-NMR spectra and (b) complete the field dependent 23Na-T1-relaxation curves in order to be able to have enough data to model the T1- and T2-dispersion and reveal information about the dynamical nature of the apparent cubic phase. In parallel, we want (b) to employ these techniques to a detailed analysis of solid solutions of BaTiO3-CaTiO3, (barium calcium titanate, BCT), its poling/depoling behavior, the precipitation hardening process and its effect on the poling/depoling process inside these materials. Our interest in this type of materials is triggered by their favorable electric loss properties.

钛酸铋钠及其与钡（100-x）（Na 1/2，Bi 1/2）TiO 3的固溶体 （x）BaTiO 3（NBT xBT）是铅基压电陶瓷的一种有前途的环保替代品。这些本质上不均匀的材料表现出小幅度和短相干长度的结构畸变，这对仅对平均结构敏感的传统方法的表征提出了挑战。因此，这些材料的结构-性能关系的关键方面仍然不清楚，例如化学修饰的作用，相变的性质（温度或电场诱导）和弛豫铁电状态的发生。在这个项目中，我们采用固态核磁共振（ssNMR）光谱，以面对这类材料所带来的挑战，并了解它们在局部范围内的结构。这将通过分析静态的一维MAS，特别是二维3QMAS NMR谱来实现，这使得能够根据23 Na和其他可用的NMR活性核存在的核相互作用来描述局部结构。相关的NMR参数的温度依赖性的调查应该揭示发生的变化的NBT-xBT组合物的局部结构，无论是非极化和极化，在整个温度范围内，从下面的去极化温度（Td）的铁电弛豫转变温度（TF R）和介电常数的最大温度（Tm）和以上。动力学方面的本地结构将调查在铁电和弛豫状态的NMR弛豫时间的调查，目的是在这些材料中存在的本地结构波动的性质的识别。第一个应用阶段的重点是用固体NMR表征（Na 1/2，Bi 1/2）TiO 3与钛酸钡（NBT xBT，0≤x≤15）固溶体的局部结构和电极化的依赖性。在第二个应用阶段，我们首先要（a）完成对NBT xBT系统中明显立方相性质的研究。为此，我们将（a）解决MAS-NMR谱中丢失边带强度的问题，以及（B）完成场相关的23 Na-T1弛豫曲线，以便能够有足够的数据来模拟T1和T2色散，并揭示有关表观立方相的动力学性质的信息。同时，我们希望（B）使用这些技术来详细分析BaTiO 3-CaTiO 3（钛酸钡钙，BCT）的固溶体、其极化/去极化行为、沉淀硬化过程及其对这些材料内部的极化/去极化过程的影响。我们对这类材料的兴趣是由其良好的电损耗特性引发的。