The electrical conductivity of (Yb1-xCax)(2)Ti2O7-delta (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 degrees C conductivity of undoped Yb2Ti2O7 is similar to 1 x 10(-3) S/cm and that of (Yb0.95Ca0.05)(2)Ti2O7-delta and (Yb0.9Ca0.1)(2)Ti2O7-delta is similar to 7 x 10(-3) S/cm. The increase in the bulk and grain boundary conductivity in the (Yb1-xCax)(2)Ti2O7-delta (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. (C) 2013 Elsevier Ltd. All rights reserved.