Thermoelectric performance enhancement by manipulation of Sr/Ti doping in two sublayers of Ca 3 Co 4 O 9
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ISSN 2226-4108 CN 10-1154/TQ
Research Article
Thermoelectric performance enhancement by manipulation of Sr/Ti doping in two sublayers of Ca3Co4O9 Li ZHANGa,†,*, Yichen LIUb,†, Thiam Teck TANb, Yi LIUa, Jian ZHENGb, Yanling YANGa, Xiaojiang HOUa, Lei FENGa, Guoquan SUOa, Xiaohui YEa, Sean LIb a
Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, School of Materials Science and Engineering, Shaanxi University of Science & Technology, Xi’an 710021, China b UNSW Materials and Manufacturing Futures Institute, School of Material Science and Engineering, The University of New South Wales, Kensington, New South Wales, 2052, Australia Received: May 29, 2020; Revised: August 18, 2020; Accepted: August 21, 2020 © The Author(s) 2020.
Abstract: Thermoelectric (TE) performance of Ca3Co4O9 (CCO) has been investigated extensively via a doping strategy in the past decades. However, the doping sites of different sublayers in CCO and their contributions to the TE performance remain unrevealed because of its strong correlated electronic system. In this work, Sr and Ti are chosen to realize doping at the [Ca2CoO3] and [CoO2] sublayers in CCO. It was found that figure of merit (ZT) at 957 K of Ti-doped CCO was improved 30% than that of undoped CCO whereas 1 at% Sr doping brought about a 150% increase in ZT as compared to undoped CCO. The significant increase in electronic conductivity and the Seebeck coefficient are attributed to the enhanced carrier concentration and spin-entropy of Co4+ originating from the Sr doping effects in [Ca2CoO3] sublayer, which are evidenced by the scanning electron microscope (SEM), Raman, Hall, and X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, the reduced thermal conductivity is attributed to the improved phonon scattering from heavier Sr doped Ca site in [Ca2CoO3] sublayer. Our findings demonstrate that doping at Ca sites of [Ca2CoO3] layer is a feasible pathway to boost TE performance of CCO material through promoting the electronic conductivity and the Seebeck coefficient, and reducing the thermal conductivity simultaneously. This work provides a deep understanding of the current limited ZT enhancement on CCO material and provides an approach to enhance the TE performance of other layered structure materials. Keywords: layered structures; manipulation doping sites; Ca3Co4O9 (CCO); spin-entropy; thermoelectric performance
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Introduction
The need for sustainable and clean energy is more † Li Zhang and Yichen Liu contributed equally to this work. * Corresponding author. E-mail: [email protected]
urgent over the past decades. Thermoelectric (TE) materials are known to convert waste heat to electricity directly, driving extensive attention in the field of energy conversion and storage. The dimensionless figure of merit (ZT) is usually used to evaluate the TE performance of materials by ZT = S2σT/κ [1], where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, temperature, and thermal conductivity,
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