Mixed n-type electronic, oxide ion, and protonic conduction in In-doped SrTi1-xRuxO3-δ

Abstract As part of a study of mixed n-type electronic and ionic conductors, the conductivities of indium doped strontium ruthenium titanates were determined. The SrTi1-x-yRuxInyO3-δ (x ​= ​0.1–0.4, y ​= ​0–0.2) compositions were prepared by conventional solid-state synthesis. Samples were determined to be of a single phase by X-ray powder diffraction and electron probe microanalysis. The temperature and pO2 dependences of the electrical conductivities were investigated by using DC and AC four-probe methods. STRIO820 and STRIO640 have conductivity of 6.4 and 5.4 Scm−1, respectively, at 900 ​°C and pO2 ​= ​1 ​atm. The conductivities of the In-doped samples under the same conditions were lower than that of SrTi1-xRuxO3-δ by around two orders of magnitude. For STRIO622, when pO2 was increased from 10−4 to 1 ​atm, the DC conductivities decreased, indicating n-type conduction. The pO2 dependence of conductivity was analyzed using the relation σT ​= ​ApO21/x ​+ ​σi. STRIO622 shows significant ionic conductivity, with σi ~0.21 Scm−1 at 1000 ​°C. The DC conductivities of STRIO622 in reducing environments (5% H2/N2 saturated with water) show protonic conduction at low temperatures. The thermal expansion coefficients (TECs) were ~8.9–11.2 ​× ​10−6 ​K−1 ​at 200 ​≤ ​T ​≤ ​990 ​°C.