Investigation of the phase composition and stability of the α-SiAlONs by the Rietveld method

Different compositions of Y- and Nd-α-SiAlONs were sintered at 1825 °C and analysed by the XRD method. The Rietveld technique was used for characterisation of the diffraction pattern and the x value of α-SiAlON, which has a composition of Rx+vSi12−(m+n)Alm+nOnN16−n (R=Y, Nd). It was shown that the method yields reliable data for the content of the rare earth cations in the α-SiAlON phase, even in mixtures of α-SiAlONs with β- or α-Si3N4, but cannot be used for the determination of the Al and/or O contents of the α-SiAlONs. On the basis of these data, the stability regions of Y- and Nd-α-SiAlONs were established. Furthermore, it was found that the solubility area of the α-SiAlONs depends on the size of the additives. It was also shown that the solubility area of the Y-α-SiAlON is extended to lower X values than those suggested in the literature.