Crystallization of a Glass‐Ceramic by Epitaxial Growth

The crystallization mechanism in a modified Li/sub 2/O-Al/sub 2/O/sub 3/-SiO/sub 2/ glass containing P/sub 2/O/sub 5/ nucleating agent was investigated by transmission electron microscopy, X-ray diffraction, and differential thermal analysis. During an initial 1000/sup 0/C treatment P/sub 2/O/sub 5/ and Li/sub 2/O react to precipitate Li/sub 3/PO/sub 4/ crystallites. At lower temperatures cristobalite, lithium metasilicate, and lithium disilicate crystallize by epitaxial growth on those Li/sub 3/PO/sub 4/ crystallites. Crystallographic orientation relations for epitaxy were determined by electron diffraction, and lattice misfits were found to be in the range -5.3 to +3.8%. These results provide the first direct proof that glass-ceramics can crystallize by epitaxial growth on heterogeneous nuclei formed from intentionally added nucleating agents.