Cubic Cell (cubic + cell)

Distribution by Scientific Domains


Selected Abstracts


Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural study

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2008
Stéphanie Albert
A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475,K, in steps of 50,K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram,Charlier development of the Debye,Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. [source]


X-ray study and structure simulation of amorphous tungsten oxide

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2002
L. A. Lugovskaya
In this work, X-ray studies of the amorphous oxide films obtained by thermal evaporation of WO3 powder in a vacuum and by anodic oxidation were carried out. X-ray diffraction patterns were obtained in the symmetric reflection geometry on a DRON-4 diffractometer (Mo K, radiation, LiF monochromator) in automatic mode. Molecular dynamics simulation of amorphous tungsten oxide atomic configurations has been carried out in the micro-canonical ensemble (NVE) for N,=,208 atoms and N,=,624 atoms, in a cubic cell, using pairwise Born,Mayer interaction potentials and periodic boundary conditions. One of the purposes of the present work is to analyze the influence of the parameters and the cutoff of the interaction potentials on the interatomic distances. The values obtained in the molecular dynamics simulation for the pair functions D(r) are compared with the experimental data for amorphous oxides in order to choose the most convenient aforesaid values. The values of the average interatomic distances and the coordination numbers obtained by both methods are also compared. The result shows that the tungsten subsystem can be well reproduced using the potential cutoff radius of about 4,Å, but the oxygen subsystem can be well reproduced when the cutoff of the potential for the W,O pairs is equal to 2.8,Å. The configuration built during the molecular dynamics experiment consists of distorted octahedra. These octahedra form chains, as in the WO3 phases of type ReO3, and hexagonal rings, of the same type as in the WO3(1/3)H2O phase, when we extract (1/3)O at every WO3 unit. The pair function D(r) and scattering intensity I(s) distribution curves calculated for simulation configurations show a satisfactory agreement with experiment. [source]


Ce20Mg19Zn81: a new structure type with a giant cubic cell

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2008
Volodymyr Pavlyuk
Icosacerium nonadecamagnesium henoctacontazinc, Ce20Mg19Zn81, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F3m, a = 21.1979,(8),Å] and represents a new structure type among the technologically important family of ternary rare earth,transition metal,magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce20Mg19Zn81 structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+Zn4+Zn4+Zn12+Ce6), B (Mg+Zn12+Ce4+Zn24+Ce4), C (Zn4+Zn12+Mg6) and D (Zn4+Zn4+Mg12+Ce6), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic-type bonding. [source]


Numerical simulation of three-dimensional free surface flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2003
V. Maronnier
Abstract A numerical model is presented for the simulation of complex fluid flows with free surfaces in three space dimensions. The model described in Maronnier et al. (J. Comput. Phys. 1999; 155(2) : 439) is extended to three dimensional situations. The mathematical formulation of the model is similar to that of the volume of fluid (VOF) method, but the numerical procedures are different. A splitting method is used for the time discretization. At each time step, two advection problems,one for the predicted velocity field and the other for the volume fraction of liquid,are to be solved. Then, a generalized Stokes problem is solved and the velocity field is corrected. Two different grids are used for the space discretization. The two advection problems are solved on a fixed, structured grid made out of small cubic cells, using a forward characteristic method. The generalized Stokes problem is solved using continuous, piecewise linear stabilized finite elements on a fixed, unstructured mesh of tetrahedrons. The three-dimensional implementation is discussed. Efficient postprocessing algorithms enhance the quality of the numerical solution. A hierarchical data structure reduces memory requirements. Numerical results are presented for complex geometries arising in mold filling. Copyright © 2003 John Wiley & Sons, Ltd. [source]