Can stacking faults in hard-sphere crystals anneal out spontaneously?

We estimate the rate at which randomly stacked hard-sphere crystals transfo rm into the thermodynamically stable face-centered cubic phase. As an input for this estimate we need both the free-energy difference between bulk fac e-centered cubic (fcc) and hexagonal close packed (hcp) phases, and the hcp -fcc interfacial free energy. The latter quantity was computed using a latt ice-switch Monte Carlo (MC) simulation method. We find the interfacial free energy to be nonzero but extremely small: 26 +/- 6.1(05)kT/sigma(2),where sigma is the particle diameter. The free energy difference between the bulk phases was calculated using two different techniques. On the basis of our simulation results we estimate that in hard-sphere colloidal suspensions mi llimeter-sized randomly stacked crystal will anneal to form essentially pur e fcc crystal on a time scale of months to years. (C) 1999 American Institu te of Physics. [S0021-9606(99)51709-1].