Lu, Z., Sinclair, D.C. orcid.org/0000-0002-8031-7678 and Reaney, I.M. orcid.org/0000-0003-3893-6544 (2015) The Influence of La Doping and Heterogeneity on the Thermoelectric Properties of Sr3Ti2O7 Ceramics. Journal of the American Ceramic Society, 99 (2). pp. 515-522. ISSN 0002-7820
Abstract
La-doping mechanisms and thermoelectric properties of Sr3Ti2O7 Ruddlesden-Popper (RP) ceramics sintered under air and flowing 5% H2 at 1773 K for 6 hours have been investigated. Changes in lattice parameters and conductivity revealed a limited interstitial anion mechanism (~1 at.%) based on La3+ + ½O2- → Sr2+ which resulted in insulating samples when processed in air. In contrast, electronic donor-doping (La3+ + e- → Sr2+) and oxygen loss [O2- → ½ O2 (g) + 2 e-] are the dominant mechanism(s) in 5% H2- sintered ceramics with a solution limit of ~5 at.%. The increased solubility limit is attributed to the formation of Ti3+ during reduction which compensates for the extra positive charge associated with La on the A-site and also to the occurrence of oxygen loss due to the reducing conditions. For 5% H2-sintered samples, an insulating surface layer formed associated with SrO volatilisation and oxygen up-take (during cooling) from the sintering. Unless removed, the insulating layer masked the conductive nature of the ceramics. In the bulk, significantly higher power factors were obtained for ceramics that 2 were phase mixtures containing highly conductive perovskite-based (Sr,La)TiO3- (ST). This highlights the superior power factor properties of reduced perovskite-type ST phases compared to reduced RP-type Sr3Ti2O7 and serves as a precaution for the need to identify low levels of highly conducting perovskite phases when exploring rare-earth doping mechanisms in RP-type phases.
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Copyright, Publisher and Additional Information: | © 2015 Wiley. This is an author produced version of a paper subsequently published in Journal of the American Ceramic Society. Uploaded in accordance with the publisher's self-archiving policy. | ||||
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Institution: | The University of Sheffield | ||||
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield) | ||||
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Depositing User: | Symplectic Sheffield | ||||
Date Deposited: | 19 Sep 2016 14:56 | ||||
Last Modified: | 24 Oct 2016 19:05 | ||||
Published Version: | http://dx.doi.org/10.1111/jace.13998 | ||||
Status: | Published | ||||
Publisher: | Wiley | ||||
Refereed: | Yes | ||||
Identification Number: | https://doi.org/10.1111/jace.13998 | ||||
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