| Oxygen Defect Application for Oxide Thermoelectrics |
| Soonil LEE |
| Korea Institute of Ceramic Engineering and Technology |
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| Perovskite materials have been studied intensively for decades due to their broad applications, most of which are requiring to be insulating for better ferroelectric properties. On the contrary, there is lack of studies on the ferroelectrics with high concentration of electronic charge carriers. This paper demonstrates ferroelectric oxides in the unusual condition where the concentration of electronic carriers is close to a metal-insulator transition; in certain structures and compositions these materials have properties of interest for oxide based thermoelectric applications. To introduce certain amount of electronic carriers in the oxides, oxygen vacancies were generated by reduction process.In the heavily reduced perovskites (BaTiO3-¥ä, SrTiO3-¥ä), tungsten bronze structured ((Sr,Ba)Nb2O6-¥ä), and perovskite layer structured (Sr2Nb2O7-¥ä) materials, thermopower and electrical conductivity anomalies are observed due to dipole moments, depending on the carrier concentration. The nonstoichiometric n-type perovskite BaTiO3−¥ä and tungsten bronze (Sr1−xBax)Nb2O6−¥ä shows that metallic-likeconductivity occurs in the paraelectric phase and the onset of ferroelectricity stabilizes semiconducting character. The (Sr1−xBax)Nb2O6−¥ä relaxor ferroelectric single crystals, which have nanopolar regions associated with intrinsic localized phonon modes, have a high thermoelectric power factor along the c-axis, showing a strong crystal anisotropic effect. The charge transport mechanism was controlled by polaron hopping conduction above the 4mm-4/mm phase transition temperature (TC), and below TC the behavior depends on the degree of reduction. The reduced SrTiO3-¥ä crystals also show a high thermoelectric power factor at room temperature, which is related with the defect heterogeneity. With this work, the complex nature of the oxygen defect engineered ferroelectrics is discussed in terms of the thermoelectric properties and coupling of ferroelectrics and thermoelectrics |
| Acknowledgements : Clive A. Randall, Gaiying Yang, Rudger H. T. Wilke, Susan Trolier-McKinstry, Shujun Zhang, Sinan Dursun, Cihangir Duran, Takashi Teranishi, Daniel J. Magagnosc, Jonathan A. Bock, Steve Perini, Paul Moses, Jeff Long, Weiguo Qu, Petro Maksymovych, Arthur P. Baddorf |
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