Crystal structure rotation photograph

Single-crystal X-ray dillraction rotation photographs and elemental analysis have been used to show that, in both the thiourea and urea host structures, the polymerization reactions are associated with significant shortening of the space occupied by each monomer unit along the tunnel direction. For example, each monomer in the... 

The structures typically obtained as a consequence of shift non-uniqueness are analogous to nematic phase liquid crystals in the sense that there exists a unique chain direction, but the monomer repeat units in neighboring chains are not well correlated in longitudinal position. As a consequence, the x-ray rotation photographs about the chain axis direction (c) display either (1) sharp hkO reflections and progressively more diffuse hk reflection with increasing Z (2) diffuse reflection for all layers combined with a few sharp hkO reflections or (3) diffuse reflections on... 

Mutual solid solubility of the binary compounds was found to be small 13 ternary compounds were observed (table 1) and the crystal structures of most of them were determined from single crystal photographs (Laue, rotation and reciprocal lattice photography). 

Typical results for the evolution of the distances R of ions from the center of the box and corresponding snapshots of the dissolution process are shown in Fig. 4. Water molecules are omitted in this figure. The dissolution process of NaCl and CsF crystals has been recorded on video tape (27), in which the movement of water molecules is included. From these the rotational, librational, and translational motions of water molecules are observed. The video pictures show the behavior of water molecules around the structure breaking chloride ions, and the slower motion of water molecules around the structure making fluoride as opposed to chloride can be seen. Color photographs of the snapshots for the dissolution of an NaCl crystal, together with water molecules, within 7 ps are shown in Fig. 5. 

Clintonite. Clintonite is the trioctahedral brittle mica with ideal composition of Ca(Mg2Al)(SiAl3)Oio(OH)2. This structure violates the Al-avoidance principle of Loew-enstein (1954). It crystallizes in H20-saturated Ca-, Al-rich, Si-poor systems under wide P-T conditions. Clintonite, usually found in metasomatic aureoles of carbonate rocks, is rare in nature because crystallization is limited to environments characterized by both alumina-rich and silica-poor bulk-rock chemistry and very low CO2 and K activities (Bucher-Nurminen 1976 Olesch and Seifert 1976 Kato et al. 1997 Grew et al. 1999). The IM polytype and IMj sequences are the most common forms. The 2Mi form is rare (Akhundov et al. 1961) and no 3T forms have been reported. Many IM crystals are twinned by 120° rotation about the normal to the 001 cleavage. Such twinning causes extra spots on precession photographs that simulate an apparent three-layer periodicity (MacKinney et al. 1988). 

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