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令人担忧的影响，将我们和我们的自然系统置于危险之中。随着英国的目标是到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，80%以上的浪费能源是以热能的形式存在的。在更可持续技术的可行途径中，直接将废热转换为电能是使我们的电力基础更可持续的一条有希望的途径，因为热能可以被视为一种可再生资源。废热丰富且普遍存在。来自家庭、汽车尾气和工业过程等来源的热量可以被回收并利用热电发电机转化为电力；安静、可靠和可扩展的固态设备不依赖化学反应或产生有毒副产品。电也可以用于制冷或冷却。热电工作是基于19世纪发现的塞贝克和帕尔蒂埃效应。这个过程可以理解为一个热端和冷端的热机，它使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，以优值系数ZT为特征的热电效率落后于其他余热能量转换技术。热电材料的广泛和实惠的应用依赖于开发具有更高zT值的更高性能的材料。为此，必须优化各种相互冲突的传输特性：高导电性、强塞贝克效应(高塞贝克系数)和低导热系数。新型材料的合成和表征对于从理论上理解提高热电性能的机理至关重要。最近的工作强调了层状结构是很有前途的热电材料。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形成阴离子的元素结合在一起，并倾向于形成层状结构。例如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。这些属性由它们的组成指定。多阴离子固体的组成和性质的调节将是获得更高效率热电的有用平台。本项目的目的是合成用于热电应用的新型层状氧化物硫化物和氧化物氮化物。在热电应用的背景下，关于这类相的现有文献很少。这些固体的组成将进行化学调整，以加深对组成如何影响结构、电子和磁性，以及最终这些多阴离子化合物的热电性能的基本理解。软合成路线也将被用来获得使用传统固态合成方法无法获得的组合物。我们将使用广泛的分析技术来表征这些新材料，包括X射线、中子能谱和磁学。这个项目属于EPSRC能源应用材料研究领域，主题是能源。

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.