Proton conduction in nitrate-based oxides and related ceramics at intermediate temperatures

The ionic conductivity and the crystal structure have been studied for two types of nitrate-based oxides and related ceramics. These materials are mainly proton conductors at intermediate temperatures, i.e. at 300 to 600°C. For type I samples, face centered cubic structures, with lattice parameters 8.545±0.0005 and 8.903±0.005 Å, were observed for RbNO₃ and CsNO₃-based samples. The type I samples have kept more or less the nitrate structures. For the type II samples, which are aluminium oxide-based ceramics, cubic structural characteristics were observed indicating a spinel structure. Ionic and proton conducting properties were investigated using complex impedance spectroscopy, and dc conductivity measurements of concentration cells and fuel cells. The highest proton conductivity for temperatures above 400°C, 10^-2 to 10^-1 S/cm, was obtained in RbNO₃ and CsNO₃-based materials. Solid state fuel cells using these materials as electrolytes have been constructed.