Rietveld refinements for calcium and yttrium containing α-sialons

Abstract

The crystal structures of calcium and yttrium containing α-sialons, Mx (Si, Al)12(N, O)16, were refined by the Rietveld analysis of their X-ray powder diffraction patterns. Rather low R factors obtained in the refinements provide conclusive evidence for a structural model proposed by the Newcastle group. In these α-sialons, the modifying cations occupy large closed interstices of the (Si, AD-(N, O) network similar structurally to that in α-Si3N4; each cation is coordinated to seven (N, O) atoms with an average M-(N, O) length of ∼0.26nm. The (Si, Al)-(N, O) bonds range in distance from 0.17 to 0.18nm (average 0.176 nm). The Rietveld method has been shown to give highly accurate occupation factors for the interstitial cations. © 1984 Chapman and Hall Ltd.