Phase relationships in neodymia and ytterbia containing SiAlONs

The Si3N4-rich corner of the phase diagrams for neodymia and ytterbia
containing sialons has been investigated by a systematic variation of
the m and n values for compositions between 0.5 and 2.0 with a step
size of 0.5. Samples requiring nitrides of the rare earth elements have
not been prepared. Sintering has been performed at 1800degreesC for one
hour in a nitrogen atmosphere of 1 MPa. The sintered samples were
characterized by X-ray diffraction analysis to identify the crystalline
phases in equilibrium with sialon. alpha- and beta-sialon, the 21R AlN
polytypoid, and N-melilite M' were found in the Nd containing system.
Materials with Yb showed the formation of alpha- and beta-sialon, and
the AIN polytypoids; 12H and 21R. The m and n values of the
alpha-sialon phase have been calculated via their lattice parameters
that were refined by a least squares routine. The occurence and
composition of the phases were used-to outline their stability region.