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

Abstract

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 1·95 × 10− 6 S cm− 1 at 600°C, which is much lower than that of Y2O3 stabilized ZrO2 (YSZ) (4·59 × 10− 3 at 600°C). It indicates that the material Ba2DyAlO5 has excellent oxygen obstruction capability.