Variation of the density observed during the pressure-induced phase transition of a single crystal of RbCl

Pressure dependence of the density of a large-size single crystal of RbCl was observed cyclicly up to 860 MPa at 294 K and 383 K. The hysteresis loop observed in the second cycle was overlapped with that in the first cycle. While clicking sound accompanying the discontinuous increase in density was produced in the forward transition both in the first and second cycles, no sound was detected in the reverse one. The time variations of density at constant pressure were observed, where the density was nearly constant in the forward transition at 294 K, whereas steady decrease was observed in the reverse transition. Separate mechanisms are proposed, that is the Martensite transition in the forward transition, and the nucleation and its growth in the reverse one. At higher temperatures the nucleation and its growth in the forward transition are also proposed.