Planar crystals

The polyethylene crystals shown in Fig. 4.11 exist as hollow pyramids made up of planar sections. Since the solvent must be evaporated away prior to electron microscopic observation, the pyramids become buckled, torn, and/ or pleated during the course of sample preparation. While the pyramidal morphology is clearly evident in Fig. 4.1 la, there is also evidence of collapse and pleating. Likewise, the ridges on the apparently planar crystals in Fig. 4.1 lb are pleats of excess material that bunches up when the pyramids collapse. 

X-ray diffraction analyses revealed a practically planar crystal structure of diphenyl-DPP with the phenyl rings twisted by only 7° out of the plane of the... 

Real crystals can contain a large variety of different types of point, line, and planar crystal defects and other entities, such as embedded particles, which interact with dislocations and can act as obstacles to glide. Solute atoms are good examples of point defects that hinder dislocation glide by acting as centers of dilation... 

Figure 6.9 The effect of a square planar crystal field on the energies of d orbitals...

Fig. 10 Routs of conductivity in Lai xCaxMn03 (highlighted), (a) In the OOA, ligands are omitted. Electron hoping is in the directions of the primitive lattice, from one metal site to another, about 4 A away, (b) Same square planar crystal lattice with ligands explicitly shown. Routs of electron transfer include ligands, about 1.5 A away from metal sites...

We used crystal field theory to order the energy-level splittings induced in the five d orbitals. The same procedure could be applied to p orbitals. Predict the level splittings (if any) induced in the three p orbitals by octahedral and square-planar crystal fields. 

The short N—C(Ph) bond (138 pm) found for (188) indicated partial doublebond character owing to electron donation by the amino-group. The conformations of triphenylphosphine in the free and solid states and the nitrile tilt angle for (189) have been calculated. The five-membered ring of (190) has been found to be significantly non-planar. Crystal and molecular structures of the ylides (191),(192),and (181) have been determined. The... 

Dolomite precipitation probably took place at relatively low temperatures (<100°C), on the basis of planar crystal fabrics (Sibley Gregg, 1987) and the dominance of monophase aqueous fluid inclusions (Goldstein Reynolds, 1994). Under such conditions, the precipitation of well-ordered dolomite is favoured by high (Mg " " + Fe " )/Ca ratios, low salinities and high carbonate alkalinity in pore fluids (Folk Land, 1975 Machel Mountjoy, 1986). Low salinity reduces ion pairing, and high COf activities facilitate dehydration of Mg " " ions. Dolomite exhibits retrograde solubility. 

Cann, 1988). A hydrothermal origin for the dolomites can also be be ruled out. The oxygen isotopic values and lack of non-planar crystal fabrics indicate relatively low preeipitation temperatures (see below), and Carboniferous volcanics at Ballyeastle pre-date deposition of the sandstones. The nearest Permian volcanies reeorded are 70 km north of Ballycastle, between Islay and Jura (Fig. 1) (see Upton et al., 1987 Hitehen et al., 1995) and 60 km to the southeast, where >600 m of lavas are reeorded in the Lame borehole (McCann, 1990). It is generally accepted that there was little hydrothermal activity associated with the Tertiary igneous eentres of western Seotland (Hudson Andrews, 1987 Searl, 1994), and there is no evidenee that the situation in northeast Ireland was any different. 

In the ideal case, very slow, indefinitely slow, crystal growth leads to perfect crystals, which also means perfect purity of the crystals. However, the indefinite slow growth is not possible in industrial applications. Faster growth leads from the perfect, flat, planar crystals to a more rough interface between melt and crystal or melt and crystal layers. 

GO FIGURE Why is the orbital the highest-energy orbital in the square-planar crystal field ... 

A FIGURE 23.34 Energies of the d orbitals in a square-planar crystal field. 

Generation of the square planar crystal field splitting pattern by starting with an octahedral crystal field and removing the ligands along the z-axis by way of a tetragonal distortion. 

Planar crystal surfaces that survive during crystal growth are the slowest growing facets the fastest growing ones disappear entirely in the evolving crystal... 

As an alternative to the use of planar crystals and multilayers, in a number of X-ray spectrometers (especially those employing synchrotron radiation or... 

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