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Impedance spectroscopy methods applied to thermoelectric materials and devices

Dr. Jorge García-Cañadas holds a BSc. in Chemistry (2000) and MPhil. in Physical Chemistry (2002) based on the electrosynthesis and chemical characterisation of conductive polymers (both at the Universidad Autónoma de Madrid, Spain). In 2002 he was at the University of Bath (UK) as a research visitor working on the preparation and characterisation by means of electrochemical methods of nanostructured electrodes for electrochromic devices. In 2003 he joined the Photovoltaic and Optoelectronic Devices Group at the Universitat Jaume I (Castellón, Spain) where he obtained his PhD in 2006 based on the preparation and development of physical models of semiconductor devices such as electrochromics, dye-sensitised solar cells and conductive polymers. After finishing his PhD he was contracted as R&D manager by the spin-off Company Xop Física S. L. at the Science Park of the Universitat Jaume I for the development of soil moisture and conductivity sensors based on semiconductor metal oxides. In 2010 he joined the Thermoelectric Group at Cardiff University where he works in the fabrication and development of instrumentation and characterisation methods for thermoelectric devices and materials. Additionally, he is also involved in the characterisation of dye-sensitised solar cells and photovoltaics. During his career he has co-authored more than 25 papers in international journals, he is the inventor of two patents and have participated in several national and European research projects.

Impedance spectroscopy is one of the most helpful techniques for the characterization of a wide range of devices (solar cells, supercapacitors, fuel cells, etc.). However, it is not extensively used in the thermoelectric field and most of existing work is mainly focused on determining the figure of merit zT. This seminar analyses the use of impedance spectroscopy as a characterization tool for thermoelectric elements and devices. The theoretical background required for the interpretation of the measurements, based on solving the heat balance equation in the frequency domain, will be presented and validated with experimental results. It will be shown that all the relevant thermoelectric parameters and thermal properties can be potentially extracted at a given temperature from the impedance spectra, i. e., the Seebeck coefficient, electrical resistivity, thermal conductivity, figure of merit (zT), specific heat, and thermal diffusivity. The simple nature of the measurements in conjunction with the advantage of obtaining all the important thermoelectric parameters opens up the possibility of establishing impedance spectroscopy as a very useful characterization method for thermoelectricity.

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