High Performance Room Temperature Thermoelectric Oxide Materials by Controlling Nanostructure

塞贝克效应是一种热电效应，通过这种效应，材料上的温度梯度被转换成电压，这种电压可以用于发电。对化石燃料和碳排放的日益关注导致对能源生产的各个方面和减少消耗的路线进行了详细的审查。热电（TE）技术，利用废热直接转化为电能，已经成为一个重要的竞争者，特别是在汽车和运输相关的应用中。热电模块采用多对n型和p型TE材料。传统的金属TE材料（如Bi2Te3和PbTe）已经有50年的历史了，但它们是基于有毒材料的，对环境的关注日益增加。此外，碲是一种稀有且日益昂贵的元素。在过去的十年里，人们对氧化物热电材料的兴趣越来越大，因为它们的结构和化学成分可以很容易地修改（以调整性能），它们在各种操作条件下都很稳定，并且具有令人鼓舞的热电性能。虽然氧化物是高温应用的候选材料，但它们也有相当大的潜力作为“室温”热电材料（室温至200℃），用于一系列家庭应用，以及多级高温热电发电机的元件。本研究旨在了解和改善以钙钛矿或尖晶石结构为主的钛基氧化物材料的热电性能；目标应用于低温（低于200摄氏度）。热电材料的转换效率用性能曲线ZT表示（其中T为温度）；ZT应该尽可能高。为了使Z值最大化，需要高塞贝克系数(S)，再加上小导热系数和高导电性。原则上，导电性可以通过改变正离子/阴离子的组成来调节。更大的挑战是同时降低热导率。然而在氧化物陶瓷中，晶格电导率主导着热传递，因为声子是热的主要载体。这为一系列减少热传导的策略提供了基础；本质上是纳米级的微结构工程，以增加声子散射。纳米结构方法将包括：自组装纳米结构（通过棘状分解）、纳米颗粒沉淀和控制晶界电导率的纳米网络。另外，热电增强也可以通过替代掺杂剂来调节电导率来实现。通过系统地研究不同纳米结构策略的影响，我们将能够理解热电氧化物中控制热传导和电子传递的机制。这项工作的一个关键特点是，我们将采用一种综合的方法，结合英国和日本合作伙伴的优势来解决材料开发问题，探索纳米结构策略，研究热电性能作为温度的函数，研究从微观结构到原子水平的结构，并从最好的材料准备测试模块，以评估其在功率模块中的热电性能。

The Seebeck effect is a thermoelectric effect whereby a temperature gradient across a material is converted to a voltage, which can be exploited for power generation. The growing concern over fossil fuels and carbon emissions has led to detailed reviews of all aspects of energy generation and routes to reduce consumption. Thermoelectric (TE) technology, utilising the direct conversion of waste heat into electric power, has emerged as a serious contender, particular for automotive and transport related applications. Thermoelectric power modules employ multiple pairs of n-type and p-type TE materials. Traditional metallic TE materials (such as Bi2Te3 and PbTe), have been available for 50 years, but are based on toxic materials over which there is increasing environmental concern. Furthermore Te is a rare and increasingly expensive element. In the past decade there has been growing interest in oxide thermoelectrics because their structures and chemistry can be readily modified (to adjust properties), they are stable under a wide variety of operating conditions and have encouraging thermoelectric properties. Whilst oxides are candidates for high temperature applications, they also have considerable potential as "room temperature" thermoelectrics (ambient to 200C) for a range of domestic applications as well as elements in multi-stage high temperature thermoelectric generators.This investigation is concerned with understanding and improving the thermoelectric properties of Ti based oxide materials having mainly perovskite or spinel structures; targeted applications are for low temperatures (less than 200C). The conversion efficiency of thermoelectric materials is characterised by the figure of merit ZT (where T is temperature); ZT should be as high as possible. To maximise the Z value requires a high Seebeck coefficient (S), coupled with small thermal conductivity and high electrical conductivity. In principle electrical conductivity can be adjusted by changes in cation/anion composition. The greater challenge is to concurrently reduce thermal conductivity. However in oxide ceramics the lattice conductivity dominates thermal transport since phonons are the main carriers of heat. This affords the basis for a range of strategies for reducing heat conduction; essentially microstructural engineering at the nanoscale to increase phonon scattering. The nanostructuring approaches will be: Self Assembly Nanostructures (by spinoidal decomposition), nanoparticles precipitation, and nanonetworks where the grain boundary conductivity is controlled. Independently, thermoelectric enhancement can also be achieved by substitution of dopants to adjust the electrical conductivity. By systematically investigating the effect of different nanostructuring strategies we will be able to understand the mechanisms controlling thermal and electron transport in thermoelectric oxides. A key feature of the work is that we will adopt an integrated approach, combining the strengths of the UK and Japanese partners to address materials development, exploring nanostructuring strategies, investigating thermoelectric properties as a function of temperature, investigating the structures from the microstructure to the atom level, and preparing test modules from the best materials to evaluate their thermoelectric performance in power modules.