abstract
Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr0.9R0.1TiO3 +/-delta (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H-2-90%N-2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 mu W m(-1) K-2 at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics.
keywords
ELECTRONIC TRANSPORT-PROPERTIES; DOPED STRONTIUM-TITANATE; DEFECT CHEMISTRY; CERAMICS; CONDUCTIVITY; POLYCRYSTALS; SYSTEM; OXIDES; LA
subject category
Chemistry; Physics
authors
Kovalevsky, AV; Yaremchenko, AA; Populoh, S; Thiel, P; Fagg, DP; Weidenkaff, A; Frade, JR
our authors
Aleksey Yaremchenko
Principal Researcher
Andrei Kavaleuski
Principal Researcher
Jorge Ribeiro Frade
Retired Professoracknowledgements
This work was supported by the FCT, Portugal (project PEst-C/CTM/LA0011/2013 and FCT Investigator program, grants IF/00302/2012 and IF/01072/2013). Financial support from the SNF-NCCR Manep, 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 M.J. de Pinho Bastos (UA) for her experimental assistance.