X-ray data for new Y-Si-Al-O-N glass ceramics

Since the 1970s an increasing number of crystalline oxynitrides have been observed as grain boundary phases in sialon ceramics. In particular, the well-known four- and five-component phases in the Y-Si-Al-O-N system have been accepted as the total picture in this system and the potential for new phases has not been considered. However, with further development of sialon glasses and glass ceramics, post-preparative heat-treatment has revealed a number of previously uncharacterised crystalline phases occurring particularly at temperatures below 1200°C. Three such phases are discussed, I_w, Q and D, all of which have been observed previously by other researchers but without X-ray diffraction data; Q-phase occurs in some rare earth as well as yttrium sialon systems. All these phases can be produced only within a limited temperature range and are critically dependent on starting composition and heat-treatment temperature, so the present data will complement those already existing for deviitrified sialon glass products, with potentially more phases yet to be identified.