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/F042787/1
• 负责人: Pamela Thomas
• 金额: $ 23.67万
• 依托单位: University of Warwick
• 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%2FF042787%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.

该建议是A.M.教授之间的合作。 Glazer（晶体学小组，克拉伦登实验室，牛津）和P.A.教授托马斯（Thomas）和史密斯（M.E. Smith）（沃里克大学物理部）。总体目的是首次建立，即尼贝特锂和诱导锂系列（以下称LNT）中实心溶液的绝对晶体结构与其一些高度不寻常的物理特性之间的关键联系。该提案中的一个特定重点和关键兴趣的重点是该系列中存在组合物，在室温下，双折射为零，因此晶体在光学上具有各向同性，但保持电极性，这是一种独特而极其奇怪的组合非线性光学功能性铁电材料中的性质。作为我们研究计划的一部分，我们打算密切研究这种引人入胜的组成，以确保在基于光学的感应应用中，这种材料是否具有异常敏感的组件，这具有很高的技术重要性和及时的相关性。对于其他LNT组成，可以通过提高温度来获得光学各向同性的点，因此在二维组成 - 温度图中存在一个零双向弗林格点的基因座线。从基本的角度来看，我们的目标是了解LNT系列中这种行为的发生，同时牢记基于组合和温度调整组合的设备的潜力。在一个全新的创新性转折中，我们将首次研究附加参数压力对LNT的结构和特性的影响，尤其是在零双向弗林格的点附近。在高架压力下，使用双重成像的微型副本，X射线衍射和固态NMR在强大的方法组合中，我们将在三维参数空间中绘制出零双向反射的轮廓的出现，以构建组成 - 表现力压力压力。 （X-T-P）图。由于LN本身具有较大的光弹性和压电系数，因此我们期望零透射点的压力依赖性极高，从而为高度敏感和可调的压力传感器开辟了潜力。我们的研究将集中于专家X射线结构分析，包括使用异常的X射线散射，包括绝对极性测定（即确定结构中中心离子的方向与电化感之间的关系）。这些研究将扩展到非接合温度和压力，以填写参数图，并提供必要的数据来解释零双重轮廓轮廓。除此之外，双重成像显微镜将用于绘制光学特性，因此，LNT组合物的零双向轮廓是温度，压力和光波长的函数。多核固态NMR将包括7LI，17O和93NB，特别是要了解八面体畸变和阳离子位移在结构 - 质体关系中起到诸如LNT家族等组成级别的晶体的作用。这些将使用为93NB NMR构建的专用探针扩展到高温，并最终以高压NMR的敏感零透射弗林格组成的压力最高为5 GPa。总而言之，该研究计划结合了最先进的方法，以在LNT系列中进行基本性质的新科学。它既可以揭示新材料物理学，又可以回答LNT X-T-P空间中的一些长期存在的问题。最终，也是最投机性的，它可能会基于未来几年中最不寻常的物理特性组合来开发设备的新动力。

项目成果

Relationship between the structure and optical properties of lithium tantalate at the zero-birefringence point

钽酸锂零双折射点结构与光学性质的关系

• DOI: 10.1063/1.4973685
• 发表时间: 2017
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: Huband S

Powder Diffraction Study of LNT

LNT 的粉末衍射研究

• 发表时间: 2011
• 作者: Steven Huband