Study of defects and structure in organic crystals of potassium hydrogen phthalate

Imperfections in the (100), (010) and (001) plates of potassium hydrogen phthalate (KC₈H₅O₄) crystals, cut from various growth zones in different blocks, have been studied by means of X-ray diffraction topography. The experimental results show that there are mainly grown-in dislocations with the Burgers vector b = [100], [110], [10] and [101], inclusion-induced dislocations with b = [100] and <110>, glide dislocations in the systems of (001) [10], (010) [110] and (010)[10], a stacking fault with fault vector R = ± 1/3[20] and fault plane (12), growth layers mostly parallel to <111> faces, and aqueous inclusions. The dependence of the defect formation on the open structure of the crystal is discussed on the basis of the structure. The variation of the glide-dislocation contrast with wavelength, obtained using synchrotron-radiation section topography, is also given. An inclusion-probed method has proved to be powerful for determining the nature of the strains with large areas caused by thermal action, through study of the black-white contrast variation of inclusions in different strained regions.