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

英国承诺到2050年实现温室气体排放量比1990年减少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。由于英国总能源消耗的大部分可归因于供暖(48%)和交通(38%)，这些显然是重要的改革目标。在国内范围内储存能源的一种可能途径是储存热量，如果需要，这些热量可以稍后转换为电力。设计用于回收或使用各种形式的能源(如动能、热能、声能或太阳能)的能源收集器，也可以在减少能源需求方面得到应用。一种适用于这两种应用的技术是热电能量发生器(TEG)。TEG通常基于塞贝克效应：当两个端子之间存在温差时，导致电流产生的物理过程。这项技术的优势包括可靠性、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质(即导热系数和电导率)之间的相互依赖关系。虽然纳米工程已经在这方面取得了一些进展，但在实现广泛的商业化之前，还有一段路要走。这一瓶颈的解决方案可以在一种新的现象中找到，这种现象涉及到热流和电子自旋流的相互作用：自旋塞贝克效应。它类似于塞贝克效应，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。这一点意义重大，因为它导致了与自旋相关的电导率的观察，这一特征可以让我们避开Wiedemann-Franz定律施加的限制，从而进一步提高TGS的效率。利用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金触点。因此，要让这种技术在经济上可行，就需要研究更便宜的替代方案。研究表明，与纯铂触头相比，在非活性铜中加入少量的铂、铋或钽可以产生类似的收获电压。因此，本研究项目的目的是探索基于自旋Seebeck效应的TGS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.