The solubility of aluminium in rare earth nitrogen melilite phases

The incorporation of Al into nitrogen (N-)melilite phases has recently been reported [Cheng and Thompson, J. Am. Ceram. Sec., 77, 143-48 (1994)]. This occurrence allows simultaneous substitution of Al and O through replacement of Al-O for Si-N bonds and therefore, may offer potential improvement to the oxidation resistance properties of original N-melilite, which in the past was a problem that deterred the utilization of N-melilite as a grain boundary phase for Si3N4-based ceramics. In this work, the techniques of X-ray diffraction, scanning electron microscopy with quantitative energy dispersive X-ray spectroscopy and solid state Al-27 and Si-29 nuclear magnetic resonance spectroscopy with magic angle spinning have been used to study the solubility of Al in the structure of neodymium and samarium N-melilite phases.