Stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) and (Tb0.9Ca0.1)2Ti2O7−δ pyrochlores under redox conditions

► Stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7 − δ (Ln=Dy, Yb; Ln=Ce, Tb) pyrochlores (air, dry and wet H2). ► The Ce-containing materials less stable under reducing conditions than Tb-containing materials. ► Exposure to 5% H2-Ar at 900 °C for 100 h had no significant effect on the conductivity of Tb samples. ► The size mismatch between Ln and Ln´ lanthanide cations affects the bulk to grain boundary conductivity ratio.