Electrical conductivity and thermal expansion of Ln-substituted SrTiO_3 for solid oxide cell electrodes and interconnects: The effect of rare-earth cation size

摘要

The present work aims to evaluate relevant effects of the size of substituting rare-earth cation on electrical conductivity and thermal expansion of donor-doped SrTiO3 as ceramic components of electrochemical solid electrolyte cells. A series of strontium titanate-based ceramics with a moderate doping level and different cation stoichiometry, Sr(0.90)Ln(0.10)TiO(3 +/-delta) and Sr(0.85)Ln(0.10)TiO(3 +/-delta) (Ln = La-Yb), are prepared under identical conditions with the final reductive treatment in 10%H-2-N-2 atmosphere at 1500 degrees C for 10 h. The solubility of rare-earth cations in the strontium sublattice of perovskite-type SrTiO3 is found to decrease with reducing ionic radius leading to a segregation of secondary pyrochlore-type Ln(2)Ti(2)O(7) phase in the case of smaller rare-earth cations (Ln = Dy-Yb). The results of electrical, dilatometric and thermogravimetric studies suggest that the size of donor Ln(3+) cation and cation stoichiometry have no evident impact on the electrical conductivity or thermal expansion behavior as long as the content of Ln(3+) is within the solubility limits. All reduced donor-doped titanate ceramics (except Yb-doped) show a similar level of electrical conductivity, 100-155 S cm(-1) at 800 degrees C, determined by the content of Ln(3+) in the strontium sublattice, and moderate thermal expansion coefficients, 11.9-12.1 ppm K-1 at 25-1100 degrees C, compatible with that of conventional solid electrolytes.