Feasibility of heat conversion to electricity by new spin Seebeck based thermoelectrics

英国承诺到2050年将温室气体排放量在1990年的基础上减少80%。目前，人们认识到，这可能源于可再生能源和现有能源的多样化组合，以及能源储存、转换和使用技术的发展。由于英国的大部分能源消耗可归因于供暖（48%）和运输（38%），这些显然是改变的重要目标。在国内规模上进行能量储存的一个可能途径是储存热量，如果需要的话，这些热量可以在以后转化为电能。旨在回收或利用各种形式的能源（如动能、热能、声学或太阳能）的能量收集器也可以在减少能源需求方面找到应用。热电发电机（TEG）是一种同时适用于这两种应用的技术。TEG通常基于塞贝克效应：当两个终端之间存在温差时产生电流的物理过程。该技术的优点包括可靠性、灵活性和相对较小的体积，但由于效率低和成本高，目前仅限于利基市场。根据Wiedemann-Franz定律，提高TEG效率的瓶颈之一是关键材料性能（即导热性和导电性）的相互依赖性。虽然纳米工程在这方面取得了一些进展，但要实现广泛的商业化仍有一段路要走。这个瓶颈的解决方案可以在一种涉及热和电子自旋电流相互作用的新现象中找到：自旋塞贝克效应。它与塞贝克效应相似，因为热梯度可以用来产生电流，但有两个主要区别：材料必须是磁性的（无论是金属的、绝缘的还是半导体的），产生的电流是自旋极化的。这是很重要的，因为它导致了自旋相关电导率的观察，这一特征可以让我们避开Wiedemann-Franz定律所施加的限制，从而进一步提高TEGs的效率。利用由自旋塞贝克效应产生的最大自旋极化电流通常需要使用昂贵的铂触点。因此，要使这种技术在经济上可行，就需要研究更便宜的替代品。研究表明，与纯铂触点相比，少量的铂、铋或钽在其他“非活性”铜中可以产生相似的收获电压。因此，本研究项目的目的是探索基于自旋塞贝克效应的teg的替代金属接触的可能性，并评估这种应用的可行性。

The UK has committed to meet an 80% reduction in greenhouse emissions relative to 1990 by 2050. Currently, it is recognised that this will likely stem from a diverse portfolio of renewable and existing energy sources as well as the development of technologies for energy storage, conversion and usage. As the majority of the UK's total energy consumption can be attributed to heating (48%) and transport (38%) these are clearly significant targets for change. One possible route for energy storage on a domestic scale is the storage of heat that could later be converted to electricity if required. Energy harvesters designed to recycle or use various forms of energy that would otherwise be wasted (such as kinetic, thermal, acoustic, or solar), could also find applications with regards to reduction of energy demands. A technology that applies to both these applications is the thermoelectric energy generator (TEG). The TEG is typically based on the Seebeck effect: a physical process that results in the generation of an electric current when a temperature difference exists between two terminals. Advantages of this technology include reliability, flexibility, and relatively small volumes, however due to low efficiencies and high costs it is currently limited to niche markets. One of the bottlenecks for improvement of the TEG efficiency is the co-dependence of the key material properties (i.e., thermal and electric conductivities) according to the Wiedemann-Franz law. Whilst some progress has been made on this by nano-engineering, there is still some way to go before widespread commercialisation becomes viable. A solution to this bottleneck could be found in a new phenomena that involves the interplay of thermal and electron spin currents: the spin Seebeck effect. It is similar to the Seebeck effect in that a thermal gradient can be used to generate a current, but with two main differences: the material must be magnetic (whether metallic, insulating or semiconducting), and the electric current generated is spin polarised. This is significant as it has led to the observation of spin dependant conductivity, a feature that could allow us to sidestep the limit imposed by the Wiedemann-Franz Law and thus improve the efficiency of TEGs further. Harnessing the maximum spin polarised current generated by the spin Seebeck effect typically requires the use of expensive platinum contacts. For such technology to become economically viable therefore would require research into cheaper alternatives. It has been shown that small amounts of platinum, bismuth or tantalum in otherwise 'inactive' copper can result in a similar harvested voltage compared to pure platinum contacts. The aim of this research project therefore, is to explore the possibility of alternative metal contacts with respect to spin Seebeck effect based TEGs and to assess the viability of such an application.