CONDUCTION IN TITANATE PYROCHLORES - ROLE OF DOPANTS

Electrical conductivity measurements have been performed on the pyrochlore compounds Y2Ti2O7, Gd2Ti2O7 and Sm2Ti2O7 as a function of temperature, oxygen fugacity and aliovalent dopant concentration. Both the magnitude and type of conduction (ionic and/or electronic) were found to be influenced by dopant size, site location (''A'' or ''B'' cation sublattice) and net dopant density. While Ca doping on the ''A'' cation sublattice (Ca'(Gd,sm,Y)) was found to increase the ionic conductivity by as much as two and half orders of magnitude, Sr and Mg dopants with larger dopant-host size mismatch induced a drop in ionic and an enhancement in electronic conductivity. Acceptor doping on the ''B'' cation sublattice, e.g. Al'(Ti), increased the ionic conduction only at low dopant levels, while RU(TI) enhanced electronic conduction at high P-O2 Trends in ionic and electronic conduction as a function of T, P-O2, and dopant density are analyzed with the aid of a defect chemical model.