Characterization of Ln4Al2O9 (Ln=Y, Sm, Eu, Gd, Tb) rare-earth aluminates as novel high-temperature barrier materials

A family of cuspidine-type rare-earth (RE) aluminates with the general formula Ln4Al2O9 (Ln= Y, Sm, Eu, Gd, Tb) was prepared for potential use as thermal-barrier coating (TBC) materials with appropriate properties. Various trivalent lanthanides were applied to tailor the properties of the oxides for use as ceramic top coat (TC) materials intended for high-temperature applications. Following various heat treatments, the X-ray diffraction (XRD) results obtained demonstrated that Eu4Al2O9 (EuAM) possessed the greatest structural stability of all the samples at 1200 and 1300 °C. Moreover, Y4Al2O9 (YAM) had a long lifetime at 1000 °C, and was stable at 1100 °C. At 1200 °C, Sm4Al2O9 (SmAM) and Gd4Al2O9 (GdAM) were more stable than Tb4Al2O9 (TbAM). However, at 300-1000 °C, the TbAM exhibited the highest thermal expansion coefficient (TEC) of all the samples. At 600 °C, the thermal diffusivity values of the five compositions were favourable, and were lower than that of yttria-stabilised zirconia (YSZ) oxides.