Crystal Phases and Lattice Dynamics of Slip-Cast β'-Sialons

Abstract

ABSTRACTThe crystal structures and phonon densities of states (DOS) of β'-Sialon ceramics, Si6-zAlzOzN8-z (0 ≤ z ≤ 6), prepared by a novel slip-cast method were studied by neutron scattering techniques. A Rietveld analysis of the diffraction patterns shows that samples of z < 4 form a single-phase solid solution of Si-A1-O-N isostructural to β-Si3N4 (space group P63/m). Within this structure there is a consistent preferred occupation of 0 on the 2c sites and N on the 6h sites. For z > 4 the materials exhibit multiple-phase structure. The observed phonon DOS of the 0 ≤ z ≤ 4 ceramics displays phonon bands at about 50 and 115 meV. These features are considerably broader than the corresponding ones in β-Si3N4 powder. As z increases, effects due to atomic disorder lead to an overlap of the two phonon bands and a complete fill up of the phonon gap at ˜100 meV.