Oxide ion conductivity of bismuth layer-structured Bi2K1−xNb2O8.5−δ

Polycrystals of Bi2K1−xNb2O8.5−δ (x=0.0−0.5), which is a member (m=2) of the bismuth layer-structured oxide (Bi2O2)2+ (Am−1BmO3m+1)2− and contains oxygen vacancies, were synthesized and their electrical conductivities were measured. By the Rietveld XRD analysis, a non-stoichiometric Bi2K0.65Nb2O8.325 was found to be a tetragonal phase and have the least amount of second phase in this system. Much higher oxide-ion conductivities were confirmed in Bi2K0.65Nb2O8.325 at a low temperature region below 700°C, compared with Bi2BaNb2O9 without extrinsic oxygen vacancies. Electronic conduction was observed at low oxygen partial pressures below 10−4 MPa at 900°C and 10−5 MPa at 600°C for Bi2K0.65Nb2O8.325.