A study was made of the cleavage and twinning character in single crystals of the chalcopyrite CuInSe2, copper indium diselenide, grown in the laboratory by a vertical Bridgman method. In this material, with a cia ratio of 2.006, the two main cleavage orientations were found to be {101} and {112} (corresponding to the descriptions {201} and {111}, respectively, in a cubic lattice). The plane identifications were made by measuring angles between adjacent cleaved surfaces and verifying the orientations by X-ray Laue and diffractometry. Cleavage was also found less frequently in a {110} plane, but here microscopic examination of the surface revealed it to consist of ridges in a [110] direction, where the microplanes on either side of a ridge edge were {112} planes. Twinning in the grown crystals was found, by angle measurements and X-ray diffraction, to occur along {112} planes, which is similar to the result in face-centred cubic, diamond and zinc blende lattices, where they are the corresponding {111} planes.
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