Thermal stability of yittrium-and-neodymium-doped alpha/beta-SiAlON ceramics

Abstract

A series of samples of yttrium and neodymium containing alpha-SiAlON (Rx+vSi12-(m+n)Alm+nOnN16-n with R = Y, Nd) has been synthesised at different temperatures and isothermal sintering times. The Rietveld technique was used for the determination of the x value of the alpha-SiAlONs. This method offers the possibility to determine the boundaries of two phase field beta-SiAlON/alpha-SiAlON with a high accuracy. On the basis of these data, the stability regions of Y- and Nd-alpha-SiAlONs were established at different temperatures. At n-values less than 0.5 x-values as low as 0.24 +/- 0.02 for Y and 0.30 +/- 0.02 for Nd-alpha-SiAlON were observed. The m values at the boundary of the stability region are nearly independent on the temperature (1650 - 1900degreesC).