Acceptor doping of Ln2Ti2O7 (Ln = Dy, Ho, Yb) pyrochlores with divalent cations (Mg, Ca, Sr, Zn)

New LANTIOX high-temperature conductors with the pyrochlore structure, (Ln1−xAx)2Ti2O7−δ (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn; x = 0, 0.01, 0.02, 0.04, 0.07, 0.1), have been prepared at 1400–1600 °C using mechanical activation, co-precipitation and solid-state reactions. Acceptor doping in the lanthanide sublattice of Ln2Ti2O7 (Ln = Dy, Ho, Yb) with Ca2+, Mg2+ and Zn2+ increases the conductivity of the titanates except in the (Ho1−xCax)2Ti2O7−δ system, where the conductivity decreases slightly at low doping levels, x = 0.01–0.02. The highest conductivity in the (Ln1−xAx)2Ti2O7−δ (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn) systems is offered by the (Ln0.9A0.1)2Ti2O7−δ and attains maximum value for (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.9Mg0.1)2Ti2O6.9 solid solutions:∼2 × 10−2 and 9 × 10−3 S cm−1 at 750 °C, respectively. Ca and Mg are best dopants for Ln2Ti2O7 (Ln = Dy, Ho, Yb) pyrochlores. Using impedance spectroscopy data, we have determined the activation energies for bulk and grain-boundary conduction in most of the (Ln1−xAx)2Ti2O7−δ (Ln = Dy, Ho; A = Ca, Mg, Zn) materials. The values obtained, 0.7–1.05 and 1–1.4 eV, respectively, are typical of oxygen ion conductors. We have also evaluated defect formation energies in the systems studied.