High Performance Room Temperature Thermoelectric Oxide Materials by Controlling Nanostructure

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.

The work will provide a foundation for the development and exploitation of room temperature (ambient to 200C) thermoelectric ceramics to generate energy via waste heat. The beneficiaries in the commercial sector are threefold: (i) ceramic manufacturers who will have new products, (ii) producers of energy management devices who will be able to develop new products for new markets, and (iii) users of thermoelectric modules, which will include domestic applications, as well as motor manufacturers, generating energy from waste heat. Policy makes will benefit from the research by knowledge of developments of environmentally friendly methods of energy generation and a way to help reduce the use of fossil fuels. There will be opportunities for museums with exhibits highlighting the principles of thermoelectric power generation and applications from automobiles to domestic environments. To the wider public there will be environmental benefits of utilising oxides in place toxic metal thermoelectrics and from the generation of energy from waste heat, leading to improved fuel consumption for automobiles and economic benefit to individuals and the UK. The research has the potential to impact the wealth and the economic competitiveness of the UK by the development of enhanced thermoelectric materials and power modules. For UK companies there will be new opportunities and new markets in the production of ceramics, the development of energy management systems, and exploitation of energy generation systems. All companies in the supply chain should become more competitive. With generation of power from waste heat in the automobile and other sectors there will be improved fuel consumption and the potential for reduction of imported oil to the UK, giving additional economic benefits. New thermoelectric power modules should be realised within 3-5 years, bringing benefits to companies in the supply chain within 3-7 years. The wider benefits of effective power generation and potential reduction of oil consumption should come within 5-10 years. The researchers working on the project will gain transferable skills in materials fabrication, microstructural and functional property characterisation, together with skills in report writing and critical analysis that will be of value in future employment. In addition to the collaborative partnership with Japan, we will establish links with UK industrial companies relevant to the supply chain, users of power generation modules, plus other academics in the field. Regular contact and news of developments will be circulated via electronic newsletters and a Workshop will be held in year 3 of the project. Non-confidential findings will be published on a project web page. Scientific and technological findings will be disseminated to the academic and industrial communities via presentations at major international conferences, including those of the International Thermoelectric Conference series, and high impact refereed publications.

With our collaborators in Japan we will jointly protect and exploit IP through the University of Manchester Technology Transfer Unit (UMIP) and the Research and Innovation Promotion Headquarters Department of AIST in Japan. The Manchester applicants (RF, CAL) have over twenty five years experience of investigating structure-property relationships in electroceramics, including thermoelectric materials. With established academic and industrial collaborators we have the necessary expertise and facilities to successfully undertake the programme of work.