NUMERICAL-SIMULATION OF ALPHA-QUARTZ UNDER NONHYDROSTATIC COMPRESSION- MEMORY GLASS AND 5-COORDINATED CRYSTALLINE PHASES

The behavior of alpha-quartz under hydrostatic and nonhydrostatic high -pressure conditions has been investigated in molecular dynamics simul ations of silica in order to clarify the role of nonhydrostatic stress es in the amorphization process. It is shown that the amorphization th reshold is not modified if the stress along the c direction is lowered , so that the mean amorphization pressure can effectively be lowered u nder nonhydrostatic conditions. On the other hand, the application of a positive uniaxial stress along the c axis results in the appearance of a new crystalline phase, where all silicon atoms are in fivefold co ordination.