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 = 0.0,0.1) has been synthesized using mechanical activation of the oxides Yb2O3, CaO, TiO2 and subsequently sintering at 1400 deg C in air, and their electrical conductivity has been measured from 300 to 950 deg C. (Yb0.9Ca0.1)2Ti2O7 synthesized at 1400 deg C from a mechanically activated oxide mixture has the highest conductivity among the pyrochlores studied so far: 2 X 10- 2 S/cm at 740 deg C, i.e., 0.2 S/cm at 1000 deg C. Neutron diffraction data indicate that the Ca2+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.