Effect of the Ca-doping on the electrical conductivity of oxide ion conductor Yb2Ti2O7

The first results are presented on heterovalent substitution of alkaline-earth cations Ca2+for Yb3+in oxide ion conductor Yb2Ti2O7. (Yb1-xCax)2Ti2O7 (x = 0.05, 0.1) has been synthesized using mechanical activation of the oxides Yb2O3, CaO, TiO2 and subsequently sintering at 1400 °C in air, and their electrical conductivity has been measured from 300 to 950 °C. (Yb0.9Ca0.1)2Ti2O7 synthesized at 1400 °C from a mechanically activated oxide mixture has the highest conductivity among the pyrochlores studied so far: 2 × 10- 2 S/cm at 740 °C, i.e., 0.2 S/cm at 1000 °C. Neutron diffraction data indicate that the Сa2+in (Yb0.9Ca0.1)2Ti2O7 occupies the ytterbium site, leading to the formation of oxygen vacancies in the O2 (48f) site and the presence of oxygens in the O3 (8b) site, normally vacant in ordered pyrochlores. No evidence of Ca substitution on the Ti site has been found.