Structural characterization of a novel spatially coherent crystalline nanocomposite obtained from a melt of KBr, RbCl, RbBr, KI and RbI salts

摘要

Large transparent bulks, grown by a pulling technique from a melt prepared by mixing equal molar fractions of KBr, RbCl, RbBr, KI and RbI salts, are characterized by X-ray diffractometry, Laue photography and low-current-field-emission high-resolution electron microscopy. The bulks consist of a multiphase crystalline material made of nanocrystallites (with a size distribution range of 5-60 nm) of three different fcc-phases. One of these phases is identified as single RbBr while the other two are discussed to be binary KI(39%): RbI(61%) and ternary KBr(47%): RbCl( 39%): RbBr(14%), respectively, with unit-cell sizes of 6.889 +/- 0.007, 7.234 +/- 0.025 and 6.631 +/- 0.005 angstrom, respectively. The lattices of the crystallites, no matter the particular phase they belong to, are spatially coherent to each other so that the normal vectors to a lattice (HKL)-plane, in different crystallites, are confined in the space within a narrow circular cone around the lattice [HKL]-direction. For this cone, the semi-apical angle was determined for the cases of HKL equal to 301, 411, 331, 401, 311, 511, 221 and 321. The ternary phase crystallites contribute mainly to the observed departure of the composite crystallographic texture from a condition of full spatial coherence.