Preparation and characterization of LnMgAl₁₁O₁₉ (Ln=La, Nd, Gd) ceramic powders

Lanthanide hexaaluminate powders of LaMgAl₁₁O₁₉ (LMA), NdMgAl₁₁O₁₉ (NMA) and GdMgAl₁₁O ₁₉ (GMA) were synthesized via the solid state reaction or sol-gel and calcination method. The LMA and NMA powders synthesized by the sol-gel and calcination method at 1600 C for 8 h exhibit a single hexaaluminate phase with magnetoplumbite structure; however, the GMA powder synthesized by the sol-gel and calcination method at 1600 C for 8 h contains both a hexaaluminate phase and a small amount of second phase GdAlO₃ with a perovskite structure. The powders synthesized by the solid state reaction method at 1500 C for 4 h have a small particle size of 1-3 μm, and a large specific surface area and a good uniformity. The powders synthesized by the sol-gel and calcination method at 1600 C for 8 h have a particle size of 5-20 μm, and exhibit to a certain extent agglomeration.