Crystallography and Properties of Lithium Niobate-Tantalate Solid Solutions:towards novel optically isotropic, electrically polar materials

铌酸锂-钽酸锂固溶体的晶体学和性质：新型光学各向同性、电极性材料

• 批准号: EP/F048254/1
• 负责人: A Glazer
• 金额: $ 36.51万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF048254%2F1
• 关键词: Crystallography; Properties; Lithium; Niobate; Tantalate

This proposal is a collaboration between Professor A.M. Glazer (Crystallography Group, Clarendon Laboratory, Oxford) and Professors P.A. Thomas and M.E.Smith (Physics Dept., University of Warwick). The overall aim is to make for the first time, the crucial link between the absolute crystal structure of solid solutions in the lithium niobate and lithium tantalate series (hereafter LNT) and some of their highly unusual physical properties. A particular focus and point of key interest in this proposal is the existence of a composition in the series where the birefringence is zero at room temperature, so that the crystals become optically isotropic and yet remain electrically polar, which is an unique and extremely odd combination of properties in a nonlinear-optical, functional ferroelectric material. As part of our research programme, we intend to investigate this fascinating composition closely with a view to establishing whether such a material has potential as an unusually sensitive component in optically-based sensing applications, which are of high technical importance and timely relevance. For other LNT compositions, the point of optical isotropy can be obtained by raising the temperature, so that a locus line of zero birefringence points exists in the two-dimensional composition-temperature map. It is our goal to understand the occurrence of this behaviour across the LNT series from a fundamental point of view, whilst keeping in mind the potential for devices based on a combination of compositional and temperature tuning. In an entirely new and innovative twist, we will investigate for the first time the effect of the additional parameter pressure on the structure and properties of LNT in general, and particularly in the vicinity of the points of zero birefringence . Using birefringent imaging microsocopy, x-ray diffraction and solid state NMR at elevated pressures in a powerful combination of methodologies, we will map out the occurrence of the contours of zero birefringence in a three-dimensional parameter space to construct a composition-temperature-pressure (x-T-P) diagram. Since LN itself has large photoelastic and piezoelectric coefficients, we expect the pressure-dependence of the zero-birefringence points to be extremely high, thereby opening up the potential for a highly-sensitive and tunable pressure sensor. Our research will concentrate on expert x-ray structural analysis including absolute polarity determination (that is determination of the relationship between the direction of off-centre ions in the structures and the sense of electrical polarization) using anomalous x-ray scattering. These studies will be extended to non-ambient temperatures and pressures in order to fill out the parameter map and give the necessary data for interpretation of the zero birefringence contours. Alongside this, birefringent imaging microscopy will be used to map out the optical properties and thus, the zero birefringence contours of LNT compositions as a function of temperature, pressure and optical wavelength. Multinuclear solid state NMR will include 7Li, 17O and 93Nb, particularly to understand the role that octahedral distortions and cation displacements play in structure-property relations for compositionally-disordered crystals such as the LNT family. These will be extended to high temperatures using a dedicated probe constructed for 93Nb NMR and ultimately, to pressures of up to 5 GPa for sensitive zero-birefringence compositions as high-pressure NMR comes on-line. In summary, this research programme combines state-of-the-art methodologies to undertake novel science of a fundamental nature on the LNT series. It will both reveal new materials physics and answer some long-standing questions in the x-T-P space for LNT. Ultimately, and most speculatively, it may provide a new impetus for the development of devices based on this most unusual combination of physical properties in future years.

该提案是AM Glazer教授（牛津大学克拉伦登实验室晶体学小组）和PA教授的合作成果托马斯和M.E.史密斯（物理系，沃里克大学）。总的目标是第一次在锂的碳酸盐和钽酸锂系列（以下简称LNT）中的固溶体的绝对晶体结构与它们的一些非常不寻常的物理性质之间建立关键联系。在该提议中的一个特别的焦点和关键兴趣点是在其中双折射在室温下为零的系列中的组合物的存在，使得晶体变得光学各向同性并且仍然保持电极性，这是非线性光学功能铁电材料中的特性的独特且极其奇怪的组合。作为我们研究计划的一部分，我们打算密切研究这种迷人的成分，以确定这种材料是否有潜力作为光学传感应用中异常敏感的成分，这具有很高的技术重要性和及时的相关性。对于其它LNT组合物，光学各向同性点可以通过升高温度来获得，使得零双折射点的轨迹线存在于二维组合物-温度图中。我们的目标是从基本的角度了解LNT系列中这种行为的发生，同时牢记基于成分和温度调整组合的设备的潜力。在一个全新的和创新的扭曲，我们将首次调查的影响，额外的参数压力的结构和性能的LNT一般，特别是在附近的点的零双折射。使用双折射成像显微镜，X射线衍射和固态NMR在高压下的一个强大的组合的方法，我们将绘制出的零双折射的轮廓在三维参数空间中的发生，构建一个组成-温度-压力（x-T-P）图。由于LN本身具有较大的光弹性和压电系数，我们预计零双折射点的压力依赖性非常高，从而为高灵敏度和可调压力传感器开辟了潜力。我们的研究将集中在专家X射线结构分析，包括绝对极性测定（即确定结构中偏离中心的离子方向与电极化方向之间的关系）使用异常X射线散射。这些研究将扩展到非环境温度和压力，以填写参数图并提供解释零双折射轮廓所需的数据。除此之外，双折射成像显微镜将用于绘制光学性质，因此，LNT组合物的零双折射轮廓作为温度、压力和光波长的函数。多核固态NMR将包括7 Li，17 O和93 Nb，特别是为了了解八面体扭曲和阳离子位移在组成无序晶体（如LNT家族）的结构-性质关系中的作用。这些将被扩展到高温使用专用探针构造的93铌NMR和最终，高达5 GPa的压力敏感零双折射组合物作为高压NMR上线。总之，该研究计划结合了最先进的方法，在LNT系列上进行基本性质的新科学。它将揭示新的材料物理学，并回答LNT在x-T-P空间中的一些长期存在的问题。最终，最具推测性的是，它可能会在未来几年为基于这种最不寻常的物理特性组合的设备的开发提供新的动力。