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

单晶弛豫铁电体在一个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的温度依赖性。这项工作的主要目的是通过研究这些系统中作为温度和频率函数的结构响应来理解这些材料特殊介电性能的起源。该项目旨在通过应用中子散射(通过爱丁堡大学)和介电测量(通过格拉斯哥大学)来表征这两个方面。该项目还将研究负µ子在块状单晶材料中的化学和价态测定中的应用。中子散射是一种对材料的整体和非破坏性探测，其原因是中子通过与原子核的弱作用力与材料相互作用。这提供了约厘米量级的束流穿透深度，并已被用于工程工业部件的表征。中子是在反应堆和加速器中产生的，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)可以作为区分中子的动量和能量传递的函数来测量，例如包括拉曼和红外在内的光学光谱学。这个项目将利用大型设施中中子仪器的最新发展来研究弛豫铁电体中的低能晶格涨落，并将它们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µ子来确定铁电材料中的化学成分的可能性，并还将区分铁、钴和锰等不同价态的单一离子。最初，该项目将涉及开发使用爱丁堡大学多区熔炉生长压电材料的技术。同时，将使用现有的量子设计PPMS在极端条件科学中心(CSEC)的现有低温设备上测试新的电容电桥设置。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声光谱仪，用于测量GHz频率尺度上的晶格涨落。这些测量将与目前使用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关联。中子提供了一种直接的动量和能量分辨的结构性质测量方法，提供了微观信息，可以与基于实验室的整体探测器相比较。在电容和中子光谱的测量中，该项目还将研究在静水压力下进行这些测量的可能性。目前的大型设施有大型压力室，可以在至少几千巴的低温和压力范围内使用。还将研究在外加电场下的测量。该项目的最后一个组成部分是调查使用负µ子进行化学成分测定。目前需要在不破坏材料的情况下确定材料的化学成分，就像EXAFS或EDX所需的那样。负µ子可以提供一个空间相关的探测器，可以用来扫描浓度。最初，该项目的这一部分将测试已知价态的标准材料。该项目的第二部分将把这一点扩展到新的松弛材料。这项工作将在STFC-ISIS中子和Muon设施中进行。

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.