Crystal lattice deformation

Central damage region, corresponding to the site where a particle first contacts with the surface, undergoes the greatest stress, which leads to crystal lattice deformation. 

Due to particles extrusion, crystal lattice deformation expands to the adjacent area, though the deformation strength reduces gradually (Figs. 10(a)-10(other hand, after impacting, the particle may retain to plow the surface for a short distance to exhaust the kinetic energy of the particle. As a result, parts of the free atoms break apart from the substrate and pile up as atom clusters before the particle. The observation is consistent with results of molecular dynamics simulation of the nanometric cutting of silicon [15] and collision of the nanoparticle with the solid surface [16]. 

When particle impacts with a solid surface, the atoms of the surface layer undergo crystal lattice deformation, and then form an atom pileup on the outlet of the impacted region. With the increase of the collision time, more craters present on the solid surface, and amorphous transition of silicon and a few crystal grains can be found in the subsurface. 

Swelling cellulose I by means of liquid ammonia and precipitating the substance leads to the formation of cellulose III, which also differs from I by virtue of its deformed crystal lattice, in which the /9-angle is approximately 58° (Legrand [26]. 

Two types of contributions to dielectric and piezoelectric properties of ferroelectric ceramics are usually distinguished [6], [9-12], One type is called an intrinsic contribution, and it is due to the distortion of the crystal lattice under an applied electric field or a mechanical stress. The second type is called an extrinsic contribution, and it results from the motion of domain walls or domain switching [8], To provide an understanding of material properties of pzt, several methods to separate the intrinsic and extrinsic contributions were proposed. These methods are indirect, and are based on measurements of the dielectric and piezoelectric properties of ferroelectric ceramics [8], [10-12], In the experiments reported in this paper a different approach is adopted, which is based on measurements of high-resolution synchrotron X-ray powder diffraction. The shift in the positions of the diffraction peaks under applied electric field gives the intrinsic lattice deformation, whereas the domain switching can be calculated from the change in peak intensities [13,14],... 

Davies RJ, Eichhom SJ, Riekel C et al (2004) Crystal lattice deformation in single poly (p-phenylene benzobisoxazole) fibres. Polymer 45 7693-7704... 

The hard-ray diffraction technique allows a fast characterization of the lattice distortions for sample size in the centimeter range or more. The spatial resolution is low, but this technique showed the predominance of excess screw dislocations to accommodate the torsion deformation in all deformed crystals. A negligible contribution of edge dislocations was evidenced, which is consistent with the loading conditions. 

The major mechanical forces that affect chemical processes—coupling P->C—are mechanical stresses or pressures that deform crystal lattices, affect the solid density and chemical potentials, and cause disaggregation or aggregation of solid particles on a macroscopic scale. The reverse coupling of the chemical effects on solids—C- P -includes a very broad category of chemical reactions in a solid state, reactions of mineral or biogenic solids with waters and atmospheric gases, and corrosion of metals. 

Much of this data has been or will be published elsewhere [5-10]. The data shows that the lattice and molecules of plastically deformed crystals experience significant and semi-permanent deformation. From this, insights are obtained that permit the development of an approximate deformed lattice potential for shocked or impacted crystals. Shear bands have been observed in shocked or impacted crystals. Some of shear bands show that molten material had been extruded from deep within the bands. These are possibly the source of the hot spots thought to be responsible for initiation during shock or impact. On the basis of these and other experimental observations it is concluded that energy dissipation and localization during plastic deformation is likely to be responsible for initiation of chemical reaction. 

Section (2) develops a theoretical account of plastic deformation and energy dissipation at the atomic or molecular level. The AFM observations show that plastic deformation of shocked or impacted crystals can significantly deform both the crystal lattice and its molecular components. These molecular and sub-molecular scale processes require a quantum mechanical description and necessarily involve the lattice and molecular potentials of the deforming crystals. A deformed lattice potential is developed which when combined with a quantum mechanical account of plastic flow in crystalline solids will be shown to give reasonably complete and accurate descriptions of the plastic flow and initiation properties of damaged and deformed explosive crystals. The deformed lattice potential allows, for the first time, the damaged state of the crystal lattice to be taken into account when determining crystal response to shock or impact. 

The recent AFM experimental data concerning plastic flow place severe restrictions on possible theoretical accounts of plastic deformation in crystalline solids due to shock or impact. The high spatial resolution of the AFM, = 2 x lO " m, reveals substantial plastic deformation in shocked or impacted crystal lattices and molecules. Understanding how this occurs and its effect on plastic flow requires a quantum mechanical description. The semi-permanent lattice deformation has necessitated the development of a deformed lattice potential which, when combined with a quantum mechanical theory of plastic deformation, makes it possible to describe many of the features found in the AFM records. Both theory and the AFM observations indicate that shock and impact are similar shear driven processes that occur at different shear stress levels and time durations. The role of pressure is to provide an applied shear stress sufficient to cause initiation. 

A number of studies has been attempted to stabilize porous silicon low-temperature oxidation in a controlled way [1-3], surface modification of silicon nanocrystallites by chemical [4] or electrochemical [5] procedures etc. Rapid thermal processing (RTP) is thought to be a shortcut method of the PS stabilization for a number of purposes. However, there is no data about RTP influence on the PS structure. Therefore, the study of lattice deformations of PS layers after RTP is of great interest. In the present work. X-ray double-crystal diffractometry was used to measure lattice deformations of PS after RTP of millisecond and second durations. 

There is no universally correct answer to the question, "What are the active sites " In many cases it may be correct to answer that the sites are all the surface platinum atoms in another, all four-coordinated surface aluminum atoms and so forth. For a long time other answers have also been given. As early as 1934 Frost and Shapiro (1 ) concluded in a review that sites are often points of crystal lattice deformation. In this connection, Erbacher showed in 1950 (14) that catalytic sites could be annealed. In 1953 Thon and Taylor (j[5) pointed out that the active site could be a dissociatively adsorbed particle, for example, an adsorbed hydrogen atom. In the 1950 s Eischens and Pliskin carried out their classic work of obtaining the infrared spectrum of adsorbed molecules and published a survey of the subject in 1958 (j ) When they observed the adsorbed molecule, they could conceivably be observing the reacting molecule and, as a result, we could be much closer to knowing the nature of the catalytic site. 

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