AVS 53rd International Symposium
    Thin Film Wednesday Sessions
       Session TF-WeM

Paper TF-WeM12
Thermoelectric Properties of Compositionally Graded Co-Doped TiO@sub 2@ Thin Films

Wednesday, November 15, 2006, 11:40 am, Room 2022

Session: Thin Films for Photovoltaics and Energy Applications
Presenter: N. Nguyen, University of Washington
Authors: N. Nguyen, University of Washington
D. Kukuruznyak, National Institute for Materials Science, Japan
A. Yamamoto, Advanced Industrial Science and Technology Institute, Japan
T. Chikyow, National Institute for Materials Science, Japan
F.S. Ohuchi, University of Washington
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There has been a recent interest in improving thermoelectric performance using segmented thermoelectric elements. Concentration gradient of dopants in the material can be regarded as a continuously segmented component composed of a single parent material. In terms of material processing, concentration gradient is more advantageous, and may result in better compatibility for device applications, especially for thin film structures. The compositionally graded Co-doped TiO@sub 2@ thin films were grown on (001) LaAlO@sub 3@ substrates by a pulsed laser deposition. Spatial distribution of the electrical resistance and thermopower mapping of the samples were mapped using a custom-designed scanning conducting probe. The Seebeck coefficients were varied from -10 µV/K to -30 µV/K, whereas the resistivity changed from 1 @Ohm@cm to 150 @Ohm@cm. The I-V characteristics under the presence of the temperature gradient were then measured by applying a current source in such a way that the thermopower current was suppressed by applying the current in the opposite direction. Power factors (S@super 2@@sigma@) were then evaluated as a function of temperature, where those for Co-doped TiO@sub 2@ were increased as compared to non-doped TiO@sub 2@ by a factor of multiple times. A part of the reason for enhancement of the power factor may relate to a spin entropy effect induced by Co doping to TiO@sub 2@. Since the maximum power factor occurs at certain temperature and/or range for given concentration of the Co-doping, the concentration graded films have an advantage to broaden the temperature range for operation with the peak performance occurring continuously over the wide temperatures of interest.