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Concurrent La and A-site vacancy doping modulates the thermoelectric response of SrTiO3: experimental and computational evidence

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posted on 03.01.2018, 09:41 authored by Feridoon Azough, Samuel S. Jackson, Dursun Ekren, Robert Freer, Marco Molinari, Stephen Yeandel, Pooja GoddardPooja Goddard, Stephen C. Parker, David Hernandez Maldonado, Demie M. Kepaptsoglou, Quentin M. Ramasse
To help understand the factors controlling the performance of one of the most promising n-type oxide thermoelectric SrTiO3, we need to explore structural control at the atomic level. In Sr1–xLa2x/3TiO3 ceramics (0.0 ≤ x ≤ 0.9), we determined that the thermal conductivity can be reduced and controlled through an interplay of La-substitution and A-site vacancies and the formation of a layered structure. The decrease in thermal conductivity with La and A-site vacancy substitution dominates the trend in the overall thermoelectric response. The maximum dimensionless figure of merit is 0.27 at 1070 K for composition x = 0.50 where half of the A-sites are occupied with La and vacancies. Atomic resolution Z-contrast imaging and atomic scale chemical analysis show that as the La content increases, A-site vacancies initially distribute randomly (x < 0.3), then cluster (x ≈ 0.5), and finally form layers (x = 0.9). The layering is accompanied by a structural phase transformation from cubic to orthorhombic and the formation of 90° rotational twins and antiphase boundaries, leading to the formation of localized supercells. The distribution of La and A-site vacancies contributes to a nonuniform distribution of atomic scale features. This combination induces temperature stable behavior in the material and reduces thermal conductivity, an important route to enhancement of the thermoelectric performance. A computational study confirmed that the thermal conductivity of SrTiO3 is lowered by the introduction of La and A-site vacancies as shown by the experiments. The modeling supports that a critical mass of A-site vacancies is needed to reduce thermal conductivity and that the arrangement of La, Sr, and A-site vacancies has a significant impact on thermal conductivity only at high La concentration.

Funding

The authors gratefully acknowledge the support and the provision of funding from EPSRC for this work (EP/H043462, EP/I036230/1, EP/L014068/1, EP/L017695/1, EP/I03601X/1, and EP/K016288/1).

History

School

  • Science

Department

  • Chemistry

Published in

ACS Applied Materials and Interfaces

Citation

AZOUGH, F. ... et al, 2017. Concurrent La and A-site vacancy doping modulates the thermoelectric response of SrTiO3: experimental and computational evidence. ACS Applied Materials and Interfaces, 9 (48), pp. 41988–42000.

Publisher

© American Chemical Society

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Acceptance date

10/11/2017

Publication date

2017

Notes

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsami.7b14231.

ISSN

1944-8244

eISSN

1944-8252

Language

en