Layered Oxides, Chalcogenides and Pnictides as Thermoelectric Materials

世界一直在通过消耗化石燃料等不可再生资源来满足日益增长的电力需求。我们对这些资源的严重依赖继续对环境产生惊人的影响，使我们和我们的自然系统都处于危险之中。由于英国的目标是到2050年实现净零碳排放，寻找更清洁、更可持续的能源变得至关重要。在英国，超过80%的浪费能源是以热能的形式存在的。在可持续发展技术的可行途径中，废热直接转化为电能是使我们的电力基础更具可持续性的有希望的途径，因为热可以被视为可再生资源。余热丰富且无处不在。来自家庭、汽车尾气和工业过程等来源的热量可以被收集起来，利用热电发电机转化为电能，而不是浪费掉；静音，可靠，可扩展的固态器件，不依赖于化学反应或产生有毒副产品。电力也可以用来为制冷或冷却提供冷却。热电原理是基于19世纪发现的塞贝克和珀尔蒂埃效应。这个过程可以理解为一个热机，有热的一面和冷的一面，利用电荷载流子作为工作介质来产生电流。相比之下，在内燃机中，燃料燃烧产生的气体是工作介质，产生机械运动。目前，热电的效率落后于其他余热能源转换技术，其特征是性能值zT。热电的广泛和可负担的应用依赖于开发具有更高zT值的高性能材料。为此，必须优化各种相互冲突的输运性质：高导电性、强塞贝克效应（高塞贝克系数）和低导热性。新材料的合成和表征对于提高热电性能机制的理论理解至关重要。最近的工作强调层状结构是有前途的热电材料。多阴离子固体含有元素周期表中的一种或多种金属元素与两种或多种阴离子形成元素结合，并倾向于形成层状结构。例子包括氧化物硫化物和氧化物氮化物。这些化合物产生了有趣的电子和磁性功能，可用于催化、电池和超导体。这些属性是由它们的组合来指定的。多阴离子固体的组成和性能的调整将为实现更高效率的热电提供一个有用的平台。本项目的目的是合成热电应用的新型层状氧化硫族化合物和氧化氮化物。在热电应用的背景下，现有的关于这种相的文献很少。这些固体的组成将在化学上进行调整，以发展对组成如何影响这些多阴离子化合物的结构、电子和磁性能以及最终热电性能的基本理解。软合成路线也将用于获得使用传统固态合成方法无法获得的组合物。广泛的分析技术将用于表征这些新材料，包括x射线和中子光谱学以及磁强计。该项目属于EPSRC能源应用材料研究领域，主题为能源。

The world has been meeting ever-growing demands for electricity through the consumption of non-renewable resources such as fossil fuels. Our crucial reliance on such sources has continues to have alarming environmental impacts, putting both us and our natural systems at risk. As the UK aims to achieve net zero carbon emissions by 2050, the search for cleaner, more sustainable energy sources has become vital.In the UK, over 80% of wasted energy is in the form of heat. Among the viable avenues for more sustainable technologies, direct waste heat-to-electricity energy conversion represents a promising route to make our electricity base more sustainable as heat can be considered a renewable resource. Waste heat is abundant and ubiquitous.Instead of going to waste, heat from sources such as homes, automotive exhausts and industrial processes could be scavenged and converted into electricity using thermoelectric generators; silent, dependable, and scalable solid-state devices which do not rely on chemical reactions or produce toxic by-products. Electricity can also be used to provide cooling for refrigeration or cooling.Thermoelectrics work based on the Seebeck and Peltier effects discovered in the 19th century. The process can be understood as a heat engine with a hot side and a cold side that uses electric charge carriers as the working medium to generate electrical current. For comparison, in an internal combustion engine, the gas produced from the combustion of fuel is the working medium, generating mechanical motion.Currently, the efficiency of thermoelectrics, characterised by the figure of merit zT, lags that of other waste heat energy-conversion technology. Broad and affordable application of thermoelectrics is reliant on developing higher performing materials with higher values of zT.For this, a variety of conflicting transport properties must be optimized: high electrical conductivity, a strong Seebeck effect (high Seebeck coefficient), and low thermal conductivity. The synthesis and characterisation of novel materials is critical to develop the theoretical understanding of the mechanisms that improve thermoelectric performance.Recent work has highlighted layered structures as promising thermoelectric materials. Multi- anion solids contain one or more metallic elements in the periodic table in combination with two or more anion-forming elements and tend to form layered structures. Examples include oxide sulfides and oxide nitrides. Such compounds give rise to interesting electronic and magnetic functionalities which can be utilised in catalysis, batteries, and superconductors. These properties are specified by their composition. The tuning of the composition and thus the properties of multi-anion solids will be a useful platform to achieve higher efficiency thermoelectrics.The proposed aim of this project is to synthesise novel layered oxide chalcogenides and oxide nitrides for thermoelectric applications. Existing literature on such phases in the context of thermoelectric applications is scarce. The compositions of these solids will be tuned chemically to develop a fundamental understanding of how composition affects structure, electronic and magnetic properties, and ultimately the thermoelectric performance in these multi-anion compounds. Soft synthetic routes will also be employed to obtain compositions that would not be accessible using traditional solid-state synthetic methods. A wide range of analytical techniques will be used to characterise these novel materials including x-ray and neutron spectroscopy and magnetometry.This project falls within the EPSRC Materials for Energy Applications research area, under the theme of Energy.