STABILITY AND ELECTRICAL CONDUCTIVITY OF PEROVSKITE PROTON CONDUCTORS IN PRESSURIZED STEAM

摘要

Perovskite oxides of composition BaCe_(0.85)Gd_(0.15)O_(3-δ) (BCG15), Ba_3Ca_(1.18)Nb_(1.82)O_(9-δ)(BCN18), and BaZr_(0.93)Y_(0.07)O_(3-δ) (BZY7) were synthesized using conventional solid-state calcining. The as-calcined powders and sintered samples were exposed to pressurized steam at various p_(H_2O) and at T ≤ 500°C. The exposed samples were subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. BCG15 powder was found to completely decompose into Gd-doped CeO_2 and BaO_2·8H_2O at P_(H_2O) ≥ 9 bars. In the case of BCN18 and BZY7, Ba (and Ca in BCN18) was preferentially leached by H_2O to form BaO_2·8H_2O (and Ca(OH)_2 in BCN18) accompanied by recrystallization from the parent perovskite structure. The perovskite structures of BCN18 and BZY7, however, remained intact at p_(H_2O) up to 306 bars. Dense samples cracked and broke after exposure to high pressure steam. The electrical resistance of the samples was also characterized. It was observed that the electrical conductivity of BCN18 at 500°C increased by a factor of ～1.8 after exposure to p_(H_2O) = 9 bars in comparison to the conductivity at p_(H_2O) = 0.3 bar.