FORMATION AND STABILITY OF BETA-QUARTZ SOLID-SOLUTION PHASE IN THE LI-SI-AL-O-N SYSTEM

The development of crystalline phases in lithium oxynitride glass-cera mics was examined, with particular emphasis placed on the effect of th e nitrogen source (AlN or Si3N4) on the formation and stability of a b eta-quartz solid-solution (ss) phase. Oxynitride glasses derived from the Li-Si-Al-O-N system were heat-treated at temperatures up to 1200 d egrees C to yield glass-ceramics in which beta-quartz(ss) and beta-spo dumene(ss) of approximate composition Li2O . Al2O3 . 4SiO(2) formed as major phases and in which X-phase (Si3Al6O12N2) and silicon oxynitrid e (Si2N2O) were present as minor phases. The nitrogen-containing beta- quartz(ss) phase that was prepared with AlN was stable at 1200 degrees C; however, the use of Si3N4 as the nitrogen source was significantly less effective in promoting such thermal stabilization. Lattice param eter measurements revealed that AlN and Si3N4 had different effects on the crystalline structures, and it was proposed that the enhanced the rmal stability of the beta-quartz(ss) phase that was prepared with AlN was due to both the replacement of oxygen by nitrogen and the positio ning of excess Al3+ ions into interstitial sites within the beta-quart z(ss) crystal lattice.