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Role of Structure and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides

DOI: 10.1021/acs.chemmater.6b03200 DOI Help

Authors: Jakub D. Baran (Department of Chemistry, University of Bath) , Demie Kepaptsoglou (SuperSTEM Laboratory) , Marco Molinari (Department of Chemistry, University of Bath) , Nuth Kulwongwit (School of Materials, University of Manchester) , Feridoon Azough (School of Materials, University of Manchester) , Robert Freer (School of Materials, University of Manchester) , Quentin M. Ramasse (SuperSTEM Laboratory) , Stephen C. Parker (Department of Chemistry, University of Bath)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials , VOL 28 , PAGES 7470 - 7478

State: Published (Approved)
Published: October 2016

Abstract: [Bi0.87SrO2]2[CoO2]1.82 (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still poorly understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking, we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then used to discuss the material’s electronic, magnetic, and transport properties. We show that Bi deficiency leads to a band gap opening and increases p-type electronic conductivity due to the formation of Co4+ species that serve as itinerant holes within the predominantly Co3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.

Subject Areas: Materials, Chemistry


Instruments: I11-High Resolution Powder Diffraction

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