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The Nature of One‐sided Intergrowths on (00 1 ) of Triclinic Centrosymmetric K 2 Cr 2 O 7 (II)
Author(s) -
Heide G.,
Follner H.,
Jackson R. A.,
Wilde P. J.
Publication year - 1996
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170310802
Subject(s) - triclinic crystal system , crystallite , crystallography , crystal twinning , crystal (programming language) , orientation (vector space) , electron diffraction , diffraction , chemistry , supersaturation , condensed matter physics , materials science , crystal structure , mathematics , physics , microstructure , optics , geometry , computer science , programming language , organic chemistry
SHUBNIKOV first observed in 1912 that centrosymmetric K 2 Cr 2 O 7 crystals (P 1 ) exhibit a growth anomaly in highly supersaturated solutions. The (001) faces of these crystals are always smooth, the parallel opposite faces are always rough. Electron micrographs show these rough surfaces to be crystallites that have grown in stacks. In Part I of this publication, the crystallite orientation was determined using electron‐induced diffraction methods. As a rule, these crystallites are parallel intergrowths. Only a small number of crystals near the surface of the host crystal are twinned according to [010]. Part II sought to ascertain the cause of these one‐sided intergrowths. To determine the most favourable energetic arrangement of two intergrown individuals, interactions across the intergrowth face as a function of shifts parallel to (001) and to (00 1 ) were calculated, 64 theoretically possible cases were considered. Only in the [010]‐twin and the seldom‐occurring [1 1 0]‐twin is an approximation of the 2/m symmetry of the macroscopic twin arrangements also found in the intergrowth structure, and this is the case only when the (00 1 ) faces of the host and guest crystal are intergrown.