Growth morphology of zinc tris(thiourea) sulphate crystals
SUNIL VERMA, M K SINGH, V K WADHAWAN and C H SURESH*
Laser Materials Division, Centre for Advanced Technology, Indore 452 013, India
The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution as zinc tris(thiourea) ions and sulphate ions.
Keywords.:Morphology of crystals; Hartman-Perdok theory; cohesive energy of crystals; ZTS crystals.
Pacs No.:81.10.Aj; 81.10.-h
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