Structure of crystalline and paracrystalline condensed matter

The experience of microparacrystals, in intermediate stages between “perfect crystalline” and “amorphous structures,” and as “building bricks” in condensed matter, has become accepted as a basic physical concept. Their existence was proven by optical and x-ray diffraction studies. A review and summary of the following aspects is presented mainly for the benefit of scientists working in the field of polymers: (1) basic features of the paracrystal; (2) types of paracrystalline distortions and their effects on the reflection profiles of the x-ray diffraction pattern; (3) the physical basis of the theory of paracrystallinity; (4) experimental determination of the paracrystalline distortion parameter g, the crystallite size L_hkt , and the α? value; (5) x-ray diffraction evidence of the existence of microparacrystals; and (6) examples of electron microscope observations of paracrystals in polymers as well as in other materials.