Chemical compatibility and oxygen-ion conductivity of Ba₂DyAlO₅ ceramic for thermal barrier coatings

Owing to its low thermal conductivity, and high thermal expansion coefficient at high-temperature, a novel ceramic Ba₂RAlO₅ (R represents rare-earth element) will be one of the candidate materials used for the thermal barrier coatings (TBCs). The chemical compatibility is critical to the durability of the TBCs system. Ba₂DyAlO₅ powder and ceramic were prepared by traditional solid state reaction and pressure-less sintering. The chemical compatibility of Ba₂DyAlO₅ with Al₂O₃ was investigated by annealing approximate diffusion couples and mixed powder at 1300, 1400, and 1500°C for 8 h, respectively. The microstructures of the interface between the Ba₂DyAlO₅/Al₂O₃ approximate diffusion couples were observed, and the phase compositions of sintered mixed powder were characterised. The oxygen-ion conductivity of the material was studied using the ac impedance spectroscopy technique over a wide temperature (400-600°C) and frequency (1 Hz-1 MHz) ranges. The results show that Ba₂DyAlO₅ and Al₂O₃ keep good chemical compatibility on the whole after heating at 1300°C for 8 h. Only a few Ba element diffuses into Al₂O₃ lattice. As the temperature increases to 1400 and 1500°C, the obvious chemical reaction occurs producing Ba₂Al₂O₄, AlDyO3 and BaO. The highest oxygen-ion conductivity of Ba₂DyAlO₅ is 1·9561026 S cm-1 at 600°C, which is much lower than that of Y2O3 stabilized ZrO₂ (YSZ) (4·5961023 at 600°C). It indicates that the material Ba₂DyAlO₅ has excellent oxygen obstruction capability.