Mixed ionci-electronic conduction in ni doped lanthanum gallate perovskites

摘要

Lanthanum, gallate is a promising material for "monolithic" fuel cells or oxygen pumps, i.e. one in which the electrolyte and electrodes are formed from a common phase. We have investigated La_(1-x)Sr_xGa_(1-y)Ni_yO_3 (LSGN_(x-)) with x chemical bounds 0.2 and 0.5 as a potential cathode material for such an electrochemical device. The sigma (PO_2, T) for LSGN_(10-2-) points to a p-type electronic conductivity at high PO_2 and predominantly ionc conductivity at low PO_2. LSGN_(10-50) has an electronic conductivity suitable for SOFC applications of approximately 50 S/cm in air at high temperature. AC impedance spectroscopy on an electron blocking cell of the form M/LSG/LSGN/LSG/M was used to isolate the ionic conductivity in the LSGN_(10-20) material. The ionic conductivity was found to have a similar magneitude and acivation energy to that of undoped LSG material with sigma _i chemical bounds 0.12 S/cm at 800 deg C and E_A chemical bounds 1.0 +- 0.1 eV. Thermal expansion measurements on the LSGN materials were characterized as a function of temperature and dopant level and were found to mathc that of the electrolyte under opeating conditions.