Characterisation of Generation II/III Piezoelectric Single Crystals for use in Sonar Transducers

单晶弛豫铁电体在前所未有的频率范围内表现出对压电系数和动力学的强烈温度依赖性。这项工作的主要目的是通过研究这些系统中的结构响应作为温度和频率的函数来了解这些材料特殊介电特性的起源。本项目旨在通过中子散射（通过爱丁堡大学）和介电测量（格拉斯哥大学）的应用来表征这两个方面。该项目还将研究负μ子在块状单晶材料化学和价态测定中的应用。中子散射是由于中子通过与原子核的弱力与物质相互作用而产生的一种非破坏性的材料体探测。这提供了厘米数量级的光束穿透深度，这已被用于工程工业部件的表征。中子在反应堆和加速器中产生，其波长和能量尺度与材料的典型激发相匹配。特别是，晶格激发（称为声子）可以作为动量和能量传递的函数来测量，从而区分中子在其他“Q=0”探针上的区别，例如包括拉曼和红外在内的光谱学。该项目将利用大规模中子仪器的最新发展来研究弛豫铁电体中的低能晶格波动，并将其与格拉斯哥大学和爱丁堡大学进行的介电测量进行比较。该项目还将探索使用负介子确定铁电体化学成分的可能性，以及区分铁、钴和锰等单一离子的不同价。最初，该项目将涉及使用爱丁堡大学的多区炉开发压电材料的生长技术。与此同时，一种新的电容桥装置将在极端条件下科学中心（CSEC）现有的低温设备上使用可用的量子设计PPMS进行测试。这将通过在格拉斯哥进行的测量以及对标准已知材料的测量来验证。该项目的第二部分将开发新的中子自旋回波光谱仪，用于测量GHz频率尺度上的晶格波动。这些测量结果将与使用当前三轴光谱仪的测量结果进行比较和联系。这些测量将作为温度的函数进行，并与上面讨论的电容测量相连接。中子提供了一种直接的动量和能量分解的结构特性测量方法，提供了可以与实验室体探针相比较的微观信息。在测量电容和中子光谱时，该项目还将研究在静水压力下进行这些测量的可能性。目前的大型设备都有大型压力电池，可以在低温和至少几千巴的压力范围下使用。还将研究外加电场下的测量。这个项目的最后一个组成部分是研究使用负介子来测定化学成分。目前需要在不像EXAFS或EDX那样破坏材料的情况下确定材料中的化学成分。负介子可以提供一种空间依赖的探针，可用于扫描浓度。最初，项目的这一部分将测试已知化合价的标准材料。项目的第二部分将扩展到新的松弛材料。这项工作将在STFC-ISIS中子和介子设施进行。

Single crystal relaxor ferroelectrics have shown a strong temperature dependence to the piezoelectric coefficient as well as dynamics over an unprecedented frequency range. The main objective of this work is to understand the origin of the exceptional dielectric properties of these materials through studying the structural response in these systems as a function of both temperature and frequency. This project will aim to characterize these two aspects through the application of neutron scattering (through the University of Edinburgh) and dielectric measurements (University of Glasgow). The project will also investigate the application of negative muons for chemical and valence determination in bulk single crystalline materials.Neutron scattering is a bulk and non-destructive probe of materials resulting from the fact that neutrons interact with material via weak forces with the nuclei. This affords beam penetration depths on the order of centimeters and this has been exploited for characterization of industrial components for engineering. Neutrons are produced at reactors and accelerators with wavelengths and energy scales that match typical excitations of materials. In particular, lattice excitations (termed phonons) can be measured as a function of momentum and energy transfer distinguishing neutrons over other "Q=0" probes such as optical spectroscopy including Raman and infrared.This project will exploit recent developments in neutron instrumentation at large scale facilities to investigate the low-energy lattice fluctuations in relaxor ferroelectrics and compare them with dielectric measurements performed at the Universities of Glasgow and Edinburgh. The project will also explore the possibility of using negative muons to determine chemical composition in ferroelectrics and also to distinguish different valency of single ions such as iron, cobalt, and manganese. Initially, the project will involve the development of growth techniques of piezoelectric materials using the multizone furnace at the University of Edinburgh. In parallel, a new capacitance bridge setup will be tested on the current low-temperature equipment at the Centre for Science at Extreme Conditions (CSEC) using an available Quantum Design PPMS. This will be validated by measurements performed at Glasgow and also on standard known materials. The second part of the project will exploit new neutron spin echo spectrometers for the measurement of lattice fluctuations on the GHz frequency scale. These measurements will be compared and connected with measurements using current triple-axis spectrometers. These measurements will be done as a function of temperature and connected with capacitance measurements discussed above. Neutrons provide a direct momentum and energy resolved measure of the structural properties providing microscopic information that can be compared with lab based bulk probes.In the measurement of both capacitance and neutron spectroscopy, the project will also investigate the possibility of performing these measurements under hydrostatic pressure. Current large facilities have large pressure cells that can be used at cryogenic temperatures and pressure scales of up to at least several kbar. Measurements under applied electric fields will also be investigated.A final component of this project is the investigation of the use of negative muons for chemical composition determination. There is a current need to determine chemical composition in materials without destroying the material like is required for EXAFS or EDX. Negative muons may provide a spatially dependent probe that can be used to scan concentration. Initially, this part of the project will test standard materials with known valency. The second part of the project will then extend this to new relaxor materials. This work will be performed at the STFC-ISIS neutron and muon facility.