Ferro- and Antiferroelectric Tetragonal Tungsten Bronzes for Capacitor Applications

用于电容器应用的铁电和反铁电四方钨青铜

• 批准号: 2449026
• 金额: --
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2449026
• 关键词: Ferro; Antiferroelectric; Tetragonal; Tungsten; Bronzes

Ferroelectricity is defined by a spontaneous polarisation which is reversible under an applied electric field. Ferroelectric (FE) materials also exhibit piezoelectricity: the material mechanically distorts under an applied voltage and also, if mechanical pressure is applied, an electric charge is generated. Ferroelectric (FE) materials are therefore used in a wide range of electronic devices including capacitors, electro-optic switches, non-volatile memory chips (a non-volatile memory retains data in the absence of power) and a number of piezoelectric (PE) transducers and sensors. While FE random access memories (FRAMs) use the two voltage-switchable polarisation states (+ve, "up" and -ve, "down") to represent binary code, PE devices convert electric fields to mechanical displacements (utilised in fuel injectors, inkjet print heads, loudspeakers), mechanical energy to electrical charge (gas ignitors, microphones), or both (medical ultrasound, sonar). Antiferroelectric materials are less common, but have potential application as multi-layer ceramic capacitors (MLCCs) in high field applications either as a result of high voltage or device miniaturisation. The current annual worldwide market for MLCCs is in excess of 4 trillion parts per annum, with growing in demand outstripping manufacture. The electronics industry is constantly seeking new ferroelectric and antiferroelectric materials. Currently the two most widely used ferroelectric (BaTiO3) and antiferroelectric (PbZrO3) materials are both perovskites and the quest for new materials has largely stayed within this family type because of the simplicity of structure and its ability to accommodate nearly every element from the periodic table.The aim of this project is to investigate the influence of composition and crystal structure on the dielectric and (anti-)ferroelectric properties of a range of materials with the tetragonal tungsten bronze (TTB - A'2A"4B'2B"8O30) structure. The TTB structure is closely related to the most widely studied perovskite (ABO3) in that it consists of a corner-sharing network of BO6 octahedra (B is typically a d-block metal), with larger cations (s-block or lanthanide) occupying the channels between octahedra. The structural, dielectric and ferroelectric properties of a range of TTB compounds will be investigated for their potential use in high voltage capacitors; these studies follow on from preliminary work already carried out in our research group. The project will involve: (solid-state) synthetic work, including ceramic processing; crystallographic structure determination using both x-ray and neutron diffraction and total scattering techniques; and electrical characterization using a range of techniques such as dielectric and impedance spectroscopy, polarization-field and thermally stimulated depolarization current measurements.

铁电性定义为在外加电场下可逆的自发极化。铁电(FE)材料也表现出压电性：材料在外加电压下机械变形，如果施加机械压力，也会产生电荷。因此，铁电(FE)材料被广泛用于各种电子设备中，包括电容器、电光开关、非易失性存储器芯片(非易失性存储器在没有电源的情况下保存数据)以及多个压电(PE)换能器和传感器。FE随机存取存储器(FRAM)使用两种电压可切换的极化状态(+Ve、“Up”和-Ve、“Down”)来表示二进制码，而PE设备将电场转换为机械位移(用于燃油喷射器、喷墨打印头、扬声器)、机械能转换为电荷(气体点火器、麦克风)，或两者兼而有之(医学超声、声纳)。反铁电材料不太常见，但由于高压或器件小型化，在高场应用中具有作为多层陶瓷电容器(MLCC)的潜在应用。目前全球MLCC的年度市场每年超过4万亿个部件，需求的增长超过了生产。电子工业一直在寻找新的铁电和反铁电材料。目前应用最广泛的两种铁电(BaTiO_3)和反铁电体(PbZrO_3)材料都是钙钛矿型，由于结构简单，几乎可以容纳元素周期表中的所有元素，因此对新材料的探索在很大程度上停留在这一家族中。本项目的目的是研究组成和晶体结构对一系列具有四方钨青铜(TTB-A‘2A“4B’2B”8O30)结构的材料的介电和(反)铁电性能的影响。TTB结构与研究最广泛的钙钛矿结构(ABO3)密切相关，因为它由BO6八面体(B通常是d-块金属)组成的角落共享网络组成，较大的阳离子(S块或稀土元素)占据了八面体之间的通道。我们将研究一系列TTB化合物的结构、介电和铁电性能，以了解它们在高压电容器中的潜在用途；这些研究是在我们课题组已经开展的前期工作的基础上进行的。该项目将涉及：(固态)合成工作，包括陶瓷加工；使用X射线和中子衍射和总散射技术确定晶体结构；以及使用介电和阻抗光谱、极化电场和热刺激去极化电流测量等一系列技术进行电气表征。