Proton Conductivity of La2(Hf2-xLax)O7-x/2 Stuffed Pyrochlores

The design of new oxygen- and proton-conducting materials is of paramount importance for their possible utilization in solid oxide fuel cells. In the present work, La-2(Hf2-xLax)O7-x/2 (x = 0, 0.1) ceramics were prepared using ball milling of oxide mixtures (La2O3 and HfO2) followed by high-temperature annealing at 1600 degrees C for 10 h in air. La2Hf2O7 ceramics exhibit an ordered pyrochlore-type structure, whereas La-2(Hf1.9La0.1)O-6.95 has a defect pyrochlore structure type with oxygen vacancies at the 48f positions. The oxygen ion and proton conductivity of La-2(Hf1.9La0.1)O-6.95 stuffed pyrochlore ceramics was investigated by electrochemical impedance spectroscopy (two-probe AC) and four-probe DC measurements in a dry and a wet atmosphere (air and nitrogen). The use of two distinct conductivity measurement techniques ensured, for the first time, the collection of reliable data on the proton conductivity of the La-2(Hf1.9La0.1)O-6.95 stuffed hafnate pyrochlore. La2Hf2O7 was found to be a dielectric in the range 400-900 degrees C, whereas the La-2(Hf1.9La0.1)O-6.95 stuffed pyrochlore had both oxygen ion and proton conductivities in this temperature range. The proton conductivity level was found to be equal to similar to 8 x 10(-5) S/cm at 700 degrees C. Clearly, the proton conductivity of the La-2(Hf1.9La0.1)O-6(.)95 stuffed hafnate pyrochlore is mainly due to the hydration of oxygen vacancies at 48f positions.

Automated summary

The design of new oxygen- and proton-conducting materials is crucial for their potential application in solid oxide fuel cells. In this study, La-2(Hf2-xLax)O7-x/2 ceramics were prepared and investigated for their conductivity properties. It was found that La-2(Hf1.9La0.1)O-6.95 stuffed pyrochlore ceramics exhibited both oxygen ion and proton conductivities.