Determination of stability areas of Yb- and Nd-alpha-SiAlON phases using the Rietveld method

A series of samples with ytterbium and neodymium contg. a-SiAlON (Rx+vSi12-(m+n)Alm+nOnN16-n with R = Yb, Nd) have been synthesized at 1800 DegC. The Rietveld technique was used for the detn. of the x value of the a-SiAlON modification. On the basis of these data, the stability regions of Yb- and Nd-a-SiAlONs were established. These results were compared with data obtained by other methods, e.g. XRD. The results show that the Rietveld method results in the most accurate data. This method offers the possibility to det. the boundaries of two phase field b-SiAlON / a-SiAlON with a high accuracy. At n values less than 0.9, x values as low as 0.25 +- 0.01 for Yb and 0.30 +- 0.01 for Nd-a-SiAlON were obsd. This is a evidence that the soly. area of the Yb-a-SiAlON is extended to lower x values than those suggested in the literature.