Crystallinity local

Crystallinity, Bulk Crystallinity, Local X-ray diffraction TEM/-selected area diffraction (SAD) Differential scanning calorimetry (DSC)... 

Keen DA, Dove MT (2000) Total scattering studies of silica polymorphs similarities in glass and disordered crystalline local structnre. Mineral Mag 64 447-457 Mary TA, Evans JSO, Vogt T, Sleight AW (1996) Negative thermal expansion from 0.3 to 1050 Kelvin in ZrW20g. Science 272 90-92... 

In the 1930 s it was shown by E. Vorlander [Trans. Faraday Soc., 29, 907 (1933)] that some liquid crystals could be quick frozen to a metastable brittle glassy state. By working with a polymeric molecule, a synthetic polypeptide called poly-y-benzyl-L-glutamate, we have been able to obtain stable solid films with a liquid crystalline local structure. These films can be obtained in conditions describable as rubbery, leathery, or glassy, as is common for polymer films. The unusual local structure of the molecules in the liquid crystalline phase gives rise to magnetic and optical properties heretofore not obtainable with polymeric systems. 

However the liquid crystalline local order can enhance and modify small solute-solvent interactions, which instead are not operative in an isotropic medium. 

Crystallization is the ordering of a disordered system. In order to follow this process, it is necessary to label atoms which have a crystalline local environment. This is done by quantifying the directional order of a system of bonds for each atom. Angular correlations at an atomic scale can be achieved by projecting interatomic vectors r, j onto a basis of spherical harmonics Yim (r ), and the order parameter of Steinhardt, Nelson, and Ronchetti has proved to be valuable in several contexts for different symmetries [32],... 

Once we have obtained classification scheme for atoms that have a crystalline local environment, it is useful to analyze their connections between these atoms. In particular, we are interested in continuous paths over these atoms (bonds) which extend over the whole system, i.e. percolation. The connection between statistical mechanics, especially phase transitions, and percolation has a vast literature. In the case of GST, simultaneous measurements of electrical resistivity and optical reflectivity showed a significant influence of percolation on electrical properties, but a negligible influence on optical properties [33]. Here, we have analyzed percolation of the simulation trajectories by locating crystalline atoms as defined above and locating continuous paths of such atoms from an atom / to the same atom in a neighboring ceii in all three Cartesian directions (for bonds of maximum length 3.20 A). 

Me2NCH2) C2H5)(Me)C-OOC Ph-HCI. Colourless crystalline powder with a bitter taste, m.p. 177-179"C. Prepared by the action of ethyl magnesium bromide on dimethyl-aminoaceione. It is a local anaesthetic, mainly used to produce spinal anaesthesia. 

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Writing by Phase Change. In an amorphous layer, crystalline marks are generated by local annealing with a focused laser beam. 

The writing process, that is, the transition crystalline — amorphous, is caused by briefly (<50 100 ns) heating up the selected storage area (diameter (( )) ca 0.5—1 Hm) by a laser pulse to a temperature above the melting point of the memory layer (Eig. 15, Record), such that the film locally melts. When cooled faster than a critical quench rate (10 -10 ° K/s), the formation of crystalline nuclei is suppressed and the melted area sohdifies into the amorphous (glass-like) state. 

In the United States, aluminum sulfate is usually produced by the reaction of bauxite or clay (qv) with sulfuric acid (see Sulfuric acid and sulfur trioxide). Bauxite is imported and more expensive than local clay, generally kaolin, which is more often used. Clay is first roasted to remove organics and break down the crystalline stmcture in order to make it more reactive. This is an energy intensive process. The purity of the starting clay or bauxite ore, especially the iron and potassium contents, are reflected in the assay of the final product. Thus the selection of the raw material is governed by the overall economics of producing a satisfying product. 

GVD Coatings. As in PVD, the stmcture of the deposited material depends on the temperature and supersaturation, roughly as pictured in Figure 8 (12). In the case of CVD, however, the effective supersaturation, ie, the local effective concentration in the gas phase of the materials to be deposited, relative to its equiUbrium concentration, depends not only on concentration, but on temperature. The reaction is thermally activated. Because the effective supersaturation for thermally activated reactions increases with temperature, the opposing tendencies can lead in some cases to a reversal of the sequence of crystalline forms Hsted in Figure 8, as temperature is increased (12). 

As is to be expected, inherent disorder has an effect on electronic and optical properties of amorphous semiconductors providing for distinct differences between them and the crystalline semiconductors. The inherent disorder provides for localized as well as nonlocalized states within the same band such that a critical energy, can be defined by distinguishing the two types of states (4). At E = E, the mean free path of the electron is on the order of the interatomic distance and the wave function fluctuates randomly such that the quantum number, k, is no longer vaHd. For E < E the wave functions are localized and for E > E they are nonlocalized. For E > E the motion of the electron is diffusive and the extended state mobiHty is approximately 10 cm /sV. For U <, conduction takes place by hopping from one localized site to the next. Hence, at U =, )J. goes through a... 

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