ON AN INTRINSIC MECHANISM OF SURFACE DEFECT FORMATION PRODUCING POLAR, MULTIDOMAIN REAL-STRUCTURES IN MOLECULAR-CRYSTALS

Dipolar but achiral organic molecules may undergo orientational disord er in the bulk but particularly at the surface of a seed crystal. In c ases where the activation energy for reversal of the dipoles in the bu lk is much larger than that for reversal at the growing crystal faces, thermodynamic arguments predict that orientational disorder occurring at surface attachment sites can produce metastable but macroscopicall y large growth sectors, featuring different polar properties than the seed. If the process of nucleation produces a non-pyroelectric symmetr y group, then orientational disorder at the surface may give rise to p yroelectric properties during subsequent growth. Similarly, for seeds belonging to a pyroelectric group, orientational disorder can reduce t he initial pyroelectric effect. According to this new surface-related mechanism of intrinsic defect formation, acentric and achiral molecule s are likely to form real-structures which show a pyroelectric effect, although from a crystallographic point of view, such crystals map be described topologically by e.g. a centric structure. These present vie ws are applied to the space group P2(1)/c, supplemented by comments on techniques available for an experimental investigation of the predict ed real-structures.