Crystallity phase relationship

Commercial submicron BT particles were modified for the study of the preferred crystal phase relationship to the corresponding dielectric properties. The results reveal that the crystal phase of the BT particles in the nanometer size range relates to the impurities incorporated in the BT crystal lattice. The responsible impurity has been identified as hydroxyls. BT is considered to meet the demands for current and future capacitor applications by modifying submicron BT particles. 

The polyamides are soluble in high strength sulfuric acid or in mixtures of hexamethylphosphoramide, /V, /V- dim ethyl acetam i de and LiCl. In the latter, compHcated relationships exist between solvent composition and the temperature at which the Hquid crystal phase forms. The polyamide solutions show an abmpt decrease in viscosity which is characteristic of mesophase formation when a critical volume fraction of polymer ( ) is exceeded. The viscosity may decrease, however, in the Hquid crystal phase if the molecular ordering allows the rod-shaped entities to gHde past one another more easily despite the higher concentration. The Hquid crystal phase is optically anisotropic and the texture is nematic. The nematic texture can be transformed to a chiral nematic texture by adding chiral species as a dopant or incorporating a chiral unit in the main chain as a copolymer (30). 

Diammonium Tetraborate Tetrahydrate. Diammonium tetraborate tetrahydrate, (NH 2 4Dy 4H2O or (NH 2D 2B202 H2O formula wt, 263.37 monoclinic sp gr, 1.58 is readily soluble ia water (Table 9). The pH of solutions of diammonium tetraborate tetrahydrate is 8.8 and iadependent of concentration. The compound is quite unstable and exhibits an appreciable vapor pressure of ammonia. Phase relationships have been outlined and the x-ray crystal stmcture formula is (NH 2P4D5(OH)J 2H20 (124). 

Diffraction is usefiil whenever there is a distinct phase relationship between scattering units. The greater the order, the better defined are the diffraction features. For example, the reciprocal lattice of a 3D crystal is a set of points, because three Laue conditions have to be exactly satisfied. The diffraction pattern is a set of sharp spots. If disorder is introduced into the structure, the spots broaden and weaken. Two-dimensional structures give diffraction rods, because only two Laue conditions have to be satisfied. The diffraction pattern is again a set of sharp spots, because the Ewald sphere cuts these rods at precise places. Disorder in the plane broadens the rods and, hence, the diffraction spots in x and y. The existence of streaks, broad spots, and additional diffuse intensity in the pattern is a common... 

Phase Relationship between the Solid and Liquid. A phase relationship may involve a number of crystalline forms from which materials can be separated. When a solid material is precipitated as a result of the solution becoming supersaturated, crystallization occurs. Crystallization may be achieved by... 

A general idea of the effect of atomic arrangement on the intensities of various reflections of a very simple crystal has been presented in an earlier section. For this crystal, ammonium chloride, the phase relationships between the waves from the two types of ions are very simple the waves from ammonium ions are, for every type of crystal plane, either exactly in phase with those from chlorine ions or exactly opposite in phase, owing to the position of the ammonium ion in the exact centre of the cube defined by the chlorine ions. 

Phase relationships in the system K O—B203—H O have been described and a portion of the phase diagram is given in Figure 8. The tetrahydrate, which can be dried at 65°C without loss of water of crystallization, begins to dehydrate between 85 and 111°C, depending on the partial pressure of water vapor in the atmosphere. This conversion is reversible and has a heat of dehydration of 86.6 kj/mol (20.7 kcal/mol) of H20. Thermogravimetric curves indicate that two moles of water are lost between 112 and 140°C, one more between 200 and 230°C and the last between 250 and 290°C (121). 

Yamada et al. [9,10] demonstrated that the copolymers were ferroelectric over a wide range of molar composition and that, at room temperature, they could be poled with an electric field much more readily than the PVF2 homopolymer. The main points highlighting the ferroelectric character of these materials can be summarized as follows (a) At a certain temperature, that depends on the copolymer composition, they present a solid-solid crystal phase transition. The crystalline lattice spacings change steeply near the transition point, (b) The relationship between the electric susceptibility e and temperature fits well the Curie-Weiss equation, (c) The remanent polarization of the poled samples reduces to zero at the transition temperature (Curie temperature, Tc). (d) The volume fraction of ferroelectric crystals is directly proportional to the remanent polarization, (e) The critical behavior for the dielectric relaxation is observed at Tc. 

It was indicated numerous times that the SHG intensity is dependent on both the magnitude of x<2) tensor elements as well as the phase relationships between fundamental and harmonic fields in the crystal. Under certain circumstances, it is possible to achieve phase matched propagation of the fundamental and harmonic beams. Under these conditions, power is continually transferred from the fundamental to harmonic beam over a path length, which is only limited by the ability... 

Figure 1 Phase relationship between the optical interference pattern and the space-charge field. For liquid crystals, this example illustrates mobile anions migrating into the nulls of the interference pattern. The application of an applied electric field Ej is usually required to observe a phase-shifted photorefractive grating.

Inversion of phase relationships induced by spin-pairing in Fe2+ ions provides one mechanism for possibly enriching this transition element in the Lower Mantle. Other, more general mechanisms influencing element fractionations, are the effects of pressure on relative sizes, crystal field stabilization energies, bond-types and oxidation states of the cations. 

In modern crystallography virtually all structure solutions are obtained by direct methods. These procedures are based on the fact that each set of hkl planes in a crystal extends over all atomic sites. The phases of all diffraction maxima must therefore be related in a unique, but not obvious, way. Limited success towards establishing this pattern has been achieved by the use of mathematical inequalities and statistical methods to identify groups of reflections in fixed phase relationship. On incorporating these into multisolution numerical trial-and-error procedures tree structures of sufficient size to solve the complete phase problem can be constructed computationally. Software to solve even macromolecular crystal structures are now available. 

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