Effect of oxygen partial pressure on the bulk and grain-boundary components of conductivity in (Yb1−xCax)2Ti2O7−δ (x = 0, 0.05, 0.1) solid solutions

• (Yb1−xCax)2Ti2O7−δ (x = 0, 0.05, 0.1) pyrochlores were investigated in a flowing O2 + N2 mixture.
• The relationship between the bulk and GB conductivities of Yb2Ti2O7 is independent of PO2.
• The active-electrode resistance drops with increasing oxygen partial pressure.
• The (Yb1−xCax)2Ti2O7−δ (x = 0, 0.05, 0.1) pyrochlores are pure oxygen ion conductors.
• The (Yb1−xCax)2Ti2O7−δ (x = 0.05, 0.1) solid solutions have high bulk conductivity.

The electrical conductivity of (Yb1−xCax)2Ti2O7−δ (x = 0, 0.05, 0.1) pyrochlore solid solutions in a flowing mixture of oxygen and nitrogen has been determined as a function of oxygen/nitrogen ratio using impedance spectroscopy. The materials are shown to be oxygen ion conductors. The 700 °C conductivity of undoped Yb2Ti2O7 is ~1 × 10−3 S/cm and that of (Yb0.95Ca0.05)2Ti2O7−δ and (Yb0.9Ca0.1)2Ti2O7−δ is ~7 × 10−3 S/cm. The increase in the bulk and grain boundary conductivity in the (Yb1−xCax)2Ti2O7−δ (x = 0, 0.05, 0.1) series is connected with a Ca doping effect, which ensures the high oxygen vacancy concentration in the grain interior and at grain boundaries.

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