Growth Mechanism and Crystal Form of Potassium Dichromate
The structure of potassium dichromate (P1, Z = 4) consists of two layers parallel to (001), between which no crystallographic symmetry relation exists. These layers are nearly coincident with each other when rotated through 90° about c * . One question remained unanswered: do the crystals grow parallel to {001} with d(002) or d(001) layers? The pseudo-fourfold axis does not run parallel to a crystallographic direction and acts only between two layers. This means that crystal growth parallel to {001} occurs in d(001) layers, which corresponds to the occurrence of one-sided intergrowths on (001). The layers are also nearly coincident with each other through pseudo-twofold axes parallel to [110] and [110], These axes do not act in the (100) or (010) projections. In the projections along the [110] and [110] directions, the lattice directions are then extended by a factor of approximately √2, and the formula units in the cell of the d(002) layer are doubled. This indicates a further possible growth mechanism. The theoretical growth forms of the crystals were calculated with the Fourier transform method of morphology.
Crystal Structure of K2Cr2O7, and a Structural Aspect of its Morphology
The structure of triclinic crystals of K-bichromate is fully determined. The structure was separated from the three-dimensional P(uvw) Patterson function by using the strong (multiple) peaks of the latter. The carefully worked out algorythm allowed the separation of 16 points of the fundamental set from the vector set (eight K atoms and eight Cr atoms). The remaining (light) atoms of the structure were localized at the second stage by reference to these latter. For the structure with 66 independent coordination parameters the divergence factor R over the entire volume of the sphere of 2500 non-zero reflections hk0-hk7 and 0kl-3kl is equal to 0138. 
 
 
 
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Growth morphology of potassium bichromate crystals from aqueous solutions
Abstract The results of a systematic study of growth morphology of potassium bichromate single crystals on seeds and by self-nucleation at different temperatures and supersaturations are presented. The observed growth morphology is analysed in the light of theoretical predictions. An increase in both growth temperature and supersaturation leads to a symmetrical morphology, and the transition from asymmetrical to symmetrical morphology is monotonous. The predicted sequence of morphological importance agrees only in the case of crystals grown at low temperatures and supersaturations.