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Lowering the thermal conductivity of Sr(Ti0.8Nb0.2)O3 by SrO and CaO doping: microstructure and thermoelectric properties

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Abstract

Excess SrO and CaO were added to the Sr(Ti0.8Nb0.2)O3 thermoelectric material, which was structurally compensated by the formation of Ruddlesden–Popper-type planar faults with the compositions SrO and/or (Sr, Ca)O. Both types of doping significantly changed the original isotropic Sr(Ti0.8Nb0.2)O3 microstructure and resulted in the formation of lamellar Ruddlesden–Popper-type phases within the Sr(Ti0.8Nb0.2)O3 grains. Three-dimensional networks of single Ruddlesden–Popper-type faults were also observed in the Sr(Ti0.8Nb0.2)O3 for both types of doping. The combination of both structural features significantly lowered the thermal conductivity in comparison with Sr(Ti0.8Nb0.2)O3 due to the enhanced phonon scattering observed at the planar faults, which proves that introducing such defects is a promising method for lowering the thermal conductivity of the Sr(Ti0.8Nb0.2)O3 thermoelectric material. The highest figure of merit (ZT = 0.08) was achieved with CaO doping, since the significantly reduced thermal conductivity was accompanied by an increased power factor.

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Acknowledgements

The authors would like to thank the Slovenian Research Agency (ARRS), project number PR-03768, and to the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement n°312483 (ESTEEM2), for the financial support of this work. Also, we would like to thank Silvo Zupančič for technical assistance in the high-temperature sintering, Medeja Gec and Andreja Šestan for TEM sample preparation, Werner Schönau for thermal conductivity measurements, and Paul McGuiness for proofreading.

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Authors and Affiliations

  1. Department for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia

    Marja Jerič & Miran Čeh

  2. Jožef Stefan Postgraduate School, Jamova 39, 1000, Ljubljana, Slovenia

    Marja Jerič

  3. Institute of Materials Research, German Aerospace Center, 51147, Cologne, Germany

    Johannes de Boor

  4. Center for Electron Microscopy and Analysis, Jamova 39, 1000, Ljubljana, Slovenia

    Janez Zavašnik & Miran Čeh

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  1. Marja Jerič
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  2. Johannes de Boor
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  3. Janez Zavašnik
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  4. Miran Čeh
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Correspondence to Marja Jerič.

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Jerič, M., de Boor, J., Zavašnik, J. et al. Lowering the thermal conductivity of Sr(Ti0.8Nb0.2)O3 by SrO and CaO doping: microstructure and thermoelectric properties. J Mater Sci 51, 7660–7668 (2016). https://doi.org/10.1007/s10853-016-0048-8

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  • DOI: https://doi.org/10.1007/s10853-016-0048-8

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