Formation of an fcc phase through a bcc metastable state in crystallization of charged colloidal particles

By in situ monitoring structural changes with the reflection spectrometer during the colloidal crystallization, we present direct experimental evidence of liquid-bcc-fcc phase transition in crystallization of charged colloidal particles, as a manifestation of the Ostwald's step rule. In addition, the lifetime of the bcc metastable structure in this system decreases significantly with increasing particle volume fraction, offering a possible explanation for exceptions to the step rule.