Effect of nanostructure on the thermal conductivity of La-doped SrTiO3 ceramics

A series of La-doped (10 at.%) SrTiO3 ceramics with grain size ranging from 6 pm to 24 nm was prepared from nanocrystalline powders using high-pressure field assisted sintering (HOP-FAST). A progressive reduction of thermal conductivity kappa with decreasing grain size was observed. At room temperature, kappa of the ceramic with grain size of 24 nm (1.2 Wm(-1) K-1) is one order of magnitude lower than that of undoped single crystals. The strong suppression of kappa can be ascribed to (i) the high concentration of lattice defects, (ii) the increasing contribution of grain boundaries to phonon scattering when the grain size is decreased to the nanoscale and (iii) a moderate amount (10-15 vol.%) of nanopores. These results demonstrate that nanostructuration can be a successful strategy to attain a considerable reduction of kappa in heavily doped bulk oxide ceramics. The low electrical conductivity of the La:SrTiO3 nanoceramics represents a major obstacle for thermoelectric applications. (C)2013 Elsevier Ltd. All rights reserved.