Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7–δ pyrochlore

The results of concentration cell electromotiveforce methods (EMF) and electrochemical impedancespectroscopy measurements on the pyrochlore systemSm1.92Ca0.08Ti2O7–δ are presented. The data have beenused to estimate total and partial conductivities anddetermine transport numbers for protons and oxide ionsunder various conditions. The EMF techniques employedinclude corrections for electrode polarisation resistance.The measurements were performed using wet and dryatmospheres in a wide pO2 range using mixtures of H2, N2,O2, and H2O in the temperature region where protonconductivity was expected (500–300 \ub0C). The impedancemeasurements revealed the conductivity to be mainly ionicunder all conditions, with the highest total conductivitymeasured being 0.045 S/m under wet oxygen at 500 \ub0C.Both bulk and grain boundary conductivity was predominantlyionic, but electronic conductivity appeared to playa slightly larger part in the grain boundaries. EMF dataconfirmed the conductivity to be mainly ionic, with oxideions being the major conducting species at 500 \ub0C and protons becoming increasingly important below thistemperature