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为可用于发电的电压。对化石燃料和碳排放的日益担忧，导致人们对能源生产的各个方面以及减少消耗的途径进行了详细的审查。热电(TE)技术利用废热直接转化为电能，已成为一个强有力的竞争者，特别是在汽车和交通相关应用中。热电功率模块采用多对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，但它们是以有毒材料为基础的，因此越来越受到环境的关注。此外，Te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与日俱增，因为它们的结构和化学成分可以很容易地进行修改(以调整性能)，它们在各种操作条件下都是稳定的，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一系列家庭应用的“室温”热电材料，以及多级高温热电发电机中的元件。本研究旨在了解和改进主要具有钙钛矿或尖晶石结构的钛基氧化物材料的热电性能；目标应用于低温(低于200℃)。热电材料的转换效率用优值系数ZT(其中T是温度)来表征；ZT应该尽可能地高。要使Z值最大化，需要高的塞贝克系数(S)，再加上小的热导率和高的电导率。原则上，电导率可以通过改变阳离子/阴离子组成来调节。更大的挑战是同时降低导热系数。然而，在氧化物陶瓷中，由于声子是热的主要载体，晶格电导主导着热的传输。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。纳米结构的方法将是：自组装纳米结构(通过螺旋体分解)，纳米粒子沉淀，以及晶界电导率可控的纳米网络。独立地，也可以通过替代掺杂来调节电导率来实现热电增强。通过系统地研究不同纳米结构策略的影响，我们将能够理解控制热电氧化物中热和电子传输的机制。这项工作的一个主要特点是，我们将采用综合方法，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，研究热电性能随温度的变化，调查从微观结构到原子水平的结构，并用最好的材料制备测试模块，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.