The high temperature proton conductor Ba3Ca1.18Nb1.82O9-δ.: I.: Electrical conductivity

The electrical conductivity of the complex perovskite Ba3Ca1.18Nb1.82O9-delta (BCN18) was systematically investigated by repeatedly charging identical samples with increasing amounts of water. Below 300 degrees C the bulk conductivity increases Linearly with the frozen-in proton concentration. The proton mobility derived from these data shows an activation energy of (0.53+/-0.01) eV and agrees with results from quasi-elastic neutron scattering. For these samples a significant grain boundary impedance is found. At temperatures below 500 degrees C the grain boundary conductivity is much smaller than the proton conduction in the grain interior and dominated by electron holes even in the wet samples. Under equilibrium conditions, i.e. for temperatures above 700 degrees C ionic transport numbers are calculated from the results of the impedance measurements. They agree with those from EMF measurements. In summary, a consistent picture of the electrical conductivity of ceramic BCN18 is derived. With respect to the grain interior excellent protonic conduction is found while the low grain boundary conductivity in our samples requires further investigations. (C) 1999 Published by Elsevier Science B.V. All rights reserved.