1 Thermoelectric properties of A-site deficient La-doped SrTiO3 at 100-900 °C under reducing conditions Sathya Prakash Singh 1 , Nikola Kanas 1 , Temesgen D. Desissa 2* , Mats Johnsson 3 , Mari- Ann Einarsrud 1 , Truls Norby 2 , and Kjell Wiik 1 1 Department of Materials Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway 2 Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, Norway 3 Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden Keywords: Thermoelectric properties, A-site deficient SrTiO3, grain size, figure-of-merit Abstract Lanthanum doped strontium titanate is a potential n-type thermoelectric material at moderate and high temperatures. (La0.12Sr0.88)0.95TiO3 ceramics were prepared by two different routes, conventional sintering at 1500 °C and spark plasma sintering at temperatures between 925 and 1200 °C. Samples with grain size between 40 nm and 1.4 µm were prepared and characterized with respect to their thermoelectric transport properties at temperatures between 100 and 900 o C under reducing conditions (H2/H2O-buffer mixtures). The thermal conductivity was significantly reduced with decreasing grain size reaching a value of 1.3 W . m -1. K -1 at 600 °C for grain size of 40 nm and porosity of 19 %. Electrical conductivity increased with increasing grain size showing a maximum of 500 S . cm -1 at 200 °C for a grain size of 1.4 µm. The highest figure-of-merit (zT) was measured for samples with 1.4 m average grain size reaching 0.2 at 500 °C. 1. Introduction The efficiency of energy systems can be improved by converting waste heat to electricity by thermoelectric generators (TEGs). These are silent and compact but have limited efficiencies as well as stability challenges under high temperature operation [1, 2]. The efficiency of a given * Present address: Department of Materials Science and Engineering, Adama Science and Technology University, P.O.Box: 1888, Adama, Ethiopia.