On the extension of the alpha-sialon phase area in yttrium and rare-earth doped systems

The extension of the alpha-sialon phase area in Y, Yb, Dy and Nd doped sialon systems has been mapped out on the basis of element analysis of individual alpha-sialon grains. The alpha-sialon-forming area expands with decreasing size of the M ion in MxSi12-(m+n)Alm+nOnN16-n. The maximum n value, n(max) is similar to 1.0 for M = Nd and similar to 1.2 for the other dopants. The m value varies from similar to 1.0 in all systems studied to a value of 2.75 in the Yb-alpha-sialon system, indicating that the substitution of Al-O units for Si-N in alpha-sialon is more restricted than substitution of Al-N for Si-N. It is shown that the lattice expansion of the alpha-sialon phase with increasing content of M ions is due to the substitution of Al-N units for Si-N, while the lattice parameters ave not at all or only very slightly dependent on the ionic radius of the M ion. Based on the elemental analysis of individual alpha-sialon grains and the lattice parameters obtained, the following empirical relation between the sizes of the a and c axes and the m and n values of the alpha-sialon phase was obtained: a(Angstrom) = 7.752 + 0.036 m + 0.02 n c(Angstrom) = 5.620 + 0.031 m + 0.04 n (C) 1997 Elsevier Science Limited.