Growth and dislocation studies of ?-HMX

<p>Background: The defect structure of organic materials is important as it plays a major role in their crystal growthproperties. It also can play a subcritical role in “hot-spot” detonation processes of energetics and one suchenergetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (?-HMX).Results: The as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, allwith {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two ofwhich could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact ofthe twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one typeof etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgersvector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated withline dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristicof mechanical deformation by dislocation slip.Conclusions: Crystals of ?-HMX grown from acetone show good morphological agreement with that predicted bymodelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution.Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant athigher super saturations. The twin plane in ?-HMX was identified as a (101) reflection plane. The low plasticity of?-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays.On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screwdislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pitsare associated with pure screw dislocations with b = [010].</p>