HIGH-DEFINITION MICROSCOPY OF PRESSURE-INDUCED NACL-CSCL TRANSITION IN RBCL

Both forward and backward phase transitions of RbCl were observed, in cases in which as-grown single crystals of RbCl were prepared even for obtaining a high-pressure phase by rearrangement of ions through the intermediary of the solution. Our high-definition microscopy revealed new characteristics of the dynamics of this well-known phenomenon: On compression, the NaCl-type single crystal was slowly transformed with retention of single crystallinity and without apparent change in cryst al shape and size. Moreover, the reverse transition was totally destru ctive; the mother single crystal of CsCl-type broke into fragments. Th ese characteristics are inconsistent with the widely accepted transiti on mechanism based on highly cooperative movement of ions.