Conductivity measurements were made of this pyrochlore compound, as a function of temperature, O partial pressure and dopant concentration. Doping additions were made, to the Gd and Ti cation sub-lattices, to levels of up to 15mol% of substituted cations. In the case of Ca doping, the conductivity increased by 2 orders of magnitude with increasing Ca content. It attained a maximum value of 0.05S/cm at 1000C, for a Ca mole fraction of 0.10. This was the highest conductivity that had been reported for a Ti-based material. The increase in conductivity was associated with a decrease in the activation energy. This fell from 0.94 to 0.63eV when the mole fraction of Ca was increased from 0 to 0.02. Similar increases in conductivity and decreases in activation energy were found for so-called B-site Al doping of Gd2(Ti1-xAlx)2Ti2O7. However, this applied only up to an Al mole fraction of 0.01. At higher dopant levels, the conductivity fell sharply when the solubility limit was exceeded. The compositional dependence of the ionic conductivity, for both A-site and B-site acceptor doping, was explained in terms of defect interactions which led to the creation of favorable transport paths.

S.A.Kramer, H.L.Tuller: Solid State Ionics, 1995, 82[1-2], 15-23