CRYSTALLINE TO NON-CRYSTALLINE TRANSFORMATION OF IRRADIATED QUARTZ.

摘要

The solid-state, irradiation-induced, crystalline to non-crystalline transformation of synthetic (alpha)-quartz was studied during in situ electron irradiation using transmission electron microscopy (TEM). The transformation proceeds in two stages: (1) rapid, heterogeneous nucleation and growth of three-dimensional amorphous inclusions, and (2) more gradual, homogeneous loss of long-range correlations in the surrounding matrix. Both of these processes were studied using convergent beam electron diffraction (CBED), high resolution structure imaging (HRSI), and as a function of temperature from (TURN)15K to (TURN)1100K.;The radiolytic production of point defects (including broken bonds and anion Frenkel pairs) results in a decrease in the connectivity of the network structure and provides topological freedom for rearrangement to an amorphous (metamict) state.;The nucleation and growth of amorphous inclusions is found to be controlled by temperature dependent point defect migration and aggregation. The amorphization of the matrix, as imaged in TEM, appears to be a surface-initiated process. The structural information obtained from CBED and HRSI indicates that short-range correlations are lost first during transformation; subsequent loss of long-range order occurs through extensive, cooperative rearrangement of the {SiO(,4)} coordination tetrahedra.