A NOVEL TITANATE-BASED OXYGEN-ION CONDUCTOR - GD2TI2O7

Electrical conductivity measurements are reported on the rare-earth py rochlore compound Gd2Ti2O7 as a function of temperature, oxygen partia l pressure and aliovalent dopant concentration. Doping experiments wer e performed on both the Gd and Ti cation sublattices with doping level s of 0.0 to 15.0 mol% cation substitution. For Ca doped (Gd1-xCax)(2)T i2O7, the ionic conductivity, sigma(i), was observed to increase over 2 orders of magnitude with increasing x reaching a maximum value of 5 x 10(-2) S/cm at 1000 degrees C and x = 0.10. This value represents th e highest ionic conductivity reported to date for a titanate based mat erial. Accompanying the increase in sigma(i) was a corresponding decre ase in ionic activation energy E(i) which dropped from 0.94 to 0.63 eV in the composition range of x = 0.00 to x = 0.02. Similar increases i n sigma(i) and decreases in E(i) were evident for ''B'' site Al doping in Gd-2(Ti1-yAly)Ti2O7 but valid only up to a doping level of y = 0.0 1. At higher dopant levels, sigma(i) dropped sharply when the solubili ty limit was exceeded, as confirmed by X-ray diffraction lattice param eter measurements. The composition dependence of the ionic conductivit y for both ''A'' and ''B'' site acceptor dopants are discussed in term s of defect interactions leading to favorable transport paths.