Design of SrTiO3-Based Thermoelectrics by Tungsten Substitution

abstract

Among n-type oxide thermoelectrics, donor-substituted strontium titanates, prepared in highly reducing conditions, show a particularly attractive thermoelectric figure of merit. High electrical conductivity, combined with outstanding redox tolerance and perovskite-phase stability of these materials, also make them prospective candidates for solid oxide fuel cell (SOFC) anode components. This work represents a first attempt to process strontium titanate ceramics with significant W for Ti substitution and to assess their relevant defect chemistry-related aspects and electrical and thermal properties, seeking mainly highly performing oxide thermoelectrics. Combined XRD/XPS/SEM/EDS studies of SrTi1-xWxO3 +/-delta (x = 0.01-0.10), prepared by a conventional solid state route, demonstrated that the maximum solubility of tungsten corresponds to 3-5% mol, depending on firing conditions and other composition changes. Separation of tungsten-containing phases on a submicro- and nanoscale level and formation of core-shell microstructures were confirmed for x >= 0.06, suggesting possibilities for tuning the thermal and electrical conductivities. Titanium cations are substituted predominantly by W6+ and partially by W5+ . High electrical conductivity and the Seebeck coefficient resulted in a maximum power factor of similar to 0.5 mW x m(-1) x K-2 for SrTi0.99W0.01O3 +/-delta; maximum ZT values, observed in the case of x = 0.01-0.06, amounted to 0.18-0.24 at 1173-1273 K. Co-substitution in Sr(Ti,Nb,W)TiO3 +/-delta materials showed good prospects for boosting thermoelectric performance in titanates, predominantly by significant reduction of the thermal conductivity.

keywords

NB-DOPED SRTIO3; STRONTIUM-TITANATE; HIGH-TEMPERATURE; FERROELECTRIC CERAMICS; ELECTRICAL-PROPERTIES; TRANSPORT-PROPERTIES; FUEL-CELLS; CONDUCTIVITY; PERFORMANCE; DEFECT

subject category

Chemistry; Science & Technology - Other Topics; Materials Science

authors

Kovalevsky, AV; Populoh, S; Patricio, SG; Thiel, P; Ferro, MC; Fagg, DP; Frade, JR; Weidenkaff, A

Groups

G3 - Electrochemical Materials, Interfaces and Coatings
G5 - Biomimetic, Biological and Living Materials

Projects

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

Centre for Research in Ceramics and Composite Materials - CICECO (LA0011: 2013-2014) (PEst-C/CTM/LA0011/2013)

acknowledgements

The work was developed in the scope of the project CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. It was partially supported by the FCT, Portugal (project PEst-C/CTM/LA0011/2013, FCT Investigator program, grant IF/00302/2012 and postdoctoral grant BPD/75943/2011). Financial support from the SNF-Sinergia project TEO, the DfG-SPP 1386, the Competence Centre Energy and Mobility (CCEM, HITTEC Project), the Swiss Federal Office of Energy (BfE), and Empa is greatly acknowledged. The authors are thankful to Prof. Carlos Sa (CEMUP) for the helpful discussion of XPS results and M.J. de Pinho Bastos (UA) for her experimental assistance.