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Face-centered Cubic (face-centered + cubic)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Concentric Sub-micrometer-Sized Cables Composed of Ni Nanowires and Sub-micrometer-Sized Fullerene Tubes,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2007
F. Tao
Abstract Highly ordered arrays of submicrometer-sized coaxial cables composed of submicrometer-sized C60 and C70 tubes filled with Ni nanowires are successfully prepared by combining a sol,gel method with an electrodeposition process. The wall thickness of the submicrometer-sized tubes can be adjusted by the concentration of fullerenes and the immersion time. The thermal stability of the submicrometer-sized C60 tubes is studied by Raman spectroscopy and it is found that these structures can be easily decomposed to form carbon nanotubes at relatively low temperatures (above 573,K) in an alumina template. These novel coaxial cable structures have been characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), field-emission SEM (FESEM), Raman spectroscopy, elemental mapping, energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), vibrating sample magnetometer (VSM) experiments, and superconducting quantum interference device (SQUID) measurements. Magnetic measurements show that these submicrometer-sized cables exhibit enhanced ferromagnetic behavior as compared to bulk nickel. Moreover, submicrometer-sized C70/Ni cables show uniaxial magnetic anisotropy with the easy magnetic axis being parallel to the long axis of the Ni nanowires. C70/Ni cables also exhibit a new magnetic transition at ca.,10,K in the magnetization,temperature (M,T) curve, which is not observed for the analogous C60/Ni structures. The origin of this transition is not yet clear, but might be related to interactions between the Ni nanowires and C70 molecules. There is no preferred magnetization axis in submicrometer-sized C60/Ni cables, which implies that the Ni nanocrystals have different packing modes in the two composites. These different crystalline packing modes lead to different magnetic anisotropy in the two composites, although the Ni nanocrystals have the same face-centered cubic (fcc) structure in both cases. [source]

Mechanisms Controlling Crystal Habits of Gold and Silver Colloids

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005
C. Lofton
Abstract Examples of gold and silver anisotropic colloids, such as prisms and rods, have appeared in the literature for many years. In most cases, the morphologies of these thermodynamically unfavorable particles have been explained by the particular reaction environment in which they were synthesized. The mechanisms used to explain the growth generally fall into two categories, one in which chemically adsorbed molecules regulate the growth of specific crystal faces kinetically, and the other where micelle-forming surfactants physically direct the shape of the particle. This paper raises questions about the growth of anisotropic metal colloids that the current mechanisms cannot adequately address, specifically, the formation of multiple shapes in a single homogeneous reaction and the appearance of similar structures in very different synthesis schemes. These observations suggest that any growth mechanism should primarily take into consideration nucleation and kinetics, and not only thermodynamics or physical constrictions. The authors suggest an alternative mechanism where the presence and orientation of twin planes in these face-centered cubic (fcc) metals direct the shape of the growing particles. This explanation follows that used for silver halide crystals, and has the advantage of explaining particle growth in many synthesis methods. In this mechanism, twin planes generate reentrant grooves, favorable sites for the attachment of adatoms. Shape and structural data are presented for gold and silver particles synthesized using several different techniques to support this new model. Triangular prisms are suggested to contain a single twin plane which directs that growth of the initial seed in two dimensions, but limits the final size of the prism. Hexagonal platelets are suggested to contain two parallel twin planes that allow the fast growing edges to regenerate one another, allowing large sizes and aspect ratios to form. Rods and wires were found to have a fivefold symmetry, which may only allow growth in one dimension. It is expected that a superior mechanistic understanding will permit shape-selective synthesis schemes to be developed. [source]

Architecture of Polymeric Superstructures Constructed by Mesoscopically Ordered Cubic Lattices

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2003
Koji Ishizu
Abstract Highly monodisperse crosslinked core-shell polymer microspheres could be prepared easily by introducing special crosslinking reagents into the segregated core in block copolymer assembly films. The crosslinked core was stabilized sterically by highly branched shell chains in solution. These microspheres moved like pseudo-latex. The microspheres formed a lattice with a body-centered cubic (BCC) structure near the overlap threshold (C*). This structure changed to a face-centered cubic (FCC) lattice in the bulk region of the films. Photofunctionalized core-shell microspheres were prepared by introducing dithiocarbamate (DC) groups into shell parts by means of polymer reactions, where DC groups could be propagated using vinyl monomers such as methyl methacrylate (MMA) with living radical mechanism. Polymeric superstructure (three microphase-separated structure) films were constructed by graft copolymerization of MMA initiated with photofunctionalized microspheres such as macroinitiators under UV irradiation, exhibiting self-coloring due to Bragg diffraction. These materials can be used for the construction of optical devices such as for the fabrication of light modulators. Photograph of a solution of the microsphere in MMA. [source]

Crystal mismatched layers in pentagonal nanorods and nanoparticles

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
L. M. Dorogin
Abstract Pentagonal nanorods (PNRs) and nanoparticles (PNPs) covered by mismatched shell layers are theoretically investigated. Mechanical stresses and elastic energies of such objects are calculated analytically and analyzed in the framework of linear isotropic elasticity. Difference between elastic modules of core and shell is taken into account. The threshold radiuses as the minimal radiuses of PNR and PNP for which the formation of the shell layer is energetically favorable are found. The threshold radius is approximately 10,nm for PNPs and 100,nm for PNRs of typical face-centered cubic (FCC) metals. The optimal magnitudes of mismatch parameter giving the maximal energy release for shelled PNRs and PNPs are determined. [source]

Compounds with a `stuffed' anti-bixbyite-type structure, analysed in terms of the Zintl,Klemm and coordination-defect concepts

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2009
Angel Vegas
The bixbyite structure (Mn2O3) () is often described as a distorted face-centered cubic (f.c.c.) array of Mn atoms, with O atoms occupying 3/4 of the tetrahedral holes. The empty M4 tetrahedra are centred at 16c. In anti-bixbyite structures (Mg3N2), cation vacancies are centred in empty N4 tetrahedra. If 16 hypothetical atoms were located at this site they would form the structure of ,-Si. This means that anti-bixbyite structures are ideally prepared to accommodate Si(Ge) atoms at these holes. Several compounds (Li3AlN2 and Li3ScN2) fully satisfy this expectation. They are really anti-bixbyites `stuffed' with Al(Sc). The presence of these atoms in 16c is illuminated in the light of the extended Zintl,Klemm concept (EZKC) [Vegas & García-Baonza (2007). Acta Cryst. B63, 339,345], from which a compound would be the result of `multiple resonance' pseudo-structures, emerging from electron transfers between any species pair (like or unlike atoms, cations or anions). The coordination-defect (CD) concept [Bevan & Martin (2008). J. Solid State Chem.181, 2250,2259] is also consistent with the EZKC description of the pseudo-structures. A more profound insight into crystal structures is gained if one is not restricted to the contemplation of classical anions and cations in their conventional oxidation states. [source]

Architecture of crystal structures from square planes

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2000
J. Hauck
The crystal structures of ordered b.c.c. (body-centered cubic), f.c.c. (face-centered cubic) or primitive cubic alloys and related NaCl, ZnS or CaF derivative structures are characterized by the self-coordination numbers , of the A atoms with A atoms. Structures with identical and values for all A atoms are at the corners of and structure maps, and can be analyzed for attractive or repulsive interactions of A atoms. Most observed structures are at the borders of the structure map and can be obtained by ,10 different combinations of structural units. The different combination mechanisms explain e.g. the shear structures of CuAu II or and the occurrence of vacancies in NaCl-related structures like NbO. [source]