Different types of defects observed inside single crystals of ciclopirox (obtained by recrystallization in ethyl acetate) are characterized. Confocal Raman spectroscopy and optical microscopy analyses revealed the coexistence of three types of defects: (i) liquid inclusions containing saturated solution with or without gas bubbles inside these inclusions, (ii) open cavities with the shape of channels, (iii) isolated gas bubbles inside the crystal matrix. It seems that the two first types of defects originate from the trapping of mother solution during crystal growth. The trapped supersaturated solution continues to crystallize inside the defect, until the formation of a negative crystal (liquid inclusion having the shape of a single crystal). This crystallization is associated with a decrease in volume, responsible in some cases for the formation of a gas bubble. However, if the liquid pocket is not sealed when the crystal is extracted from the mother solution, it produces open channels by evaporation of the solvent. The formation of isolated gas bubbles seems to result from another mechanism.
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