Coexistence of rhcp and fcc phases in hard-sphere colloidal crystalsI. P. Dolbnya1, 2, A. V. Petukhov1, D. G. A. L. Aarts1, G. J. Vroege1 and H. N. W. Lekkerkerker1
1 Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute Utrecht University - Padualaan 8, 3584 CH Utrecht, The Netherlands
2 DUBBLE CRG/ESRF, The Netherlands Organisation for Scientific Research ESRF - BP 220, F-38043 Grenoble Cedex, France
received 18 March 2005; accepted in final form 13 October 2005
published online 11 November 2005
We present results for high-resolution small-angle single-crystal X-ray diffraction of hard-sphere silica colloidal crystals. Our results indicate that the stacking probability of finding an fcc stacking sequence in a strongly compressed sample can only have two discrete values of either 0.5 (for rhcp) or 1 (for fcc) in contrast to previous observations on more dilute systems that metastable hard-sphere rhcp crystals may have various values of . This suggests that, in a concentrated sample, the transition from rhcp to fcc does not go by a smooth variation of , but through a rearrangement mechanism via melting, which leads to the formation of perfect fcc crystallites. These crystallites do not possess a single stacking fault as evidenced by the absence of twin fcc reflections.
61.10.-i - X-ray diffraction and scattering.
82.70.Dd - Colloids.
61.72.Nn - Stacking faults and other planar or extended defects.
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