Orientationally disordered crystalline

Studies on crystalline CggO [39] using calorimetry and high-resolution X-ray powder diffraction show a face centered cubic lattice (a = 14.185 A) with an orientational disorder at room temperature. An orientational ordering transition occurs at 278 K, upon which a simple cubic phase develops. At 19 K this phase, which is similar to the orientational ordered phase of Cgg itself, shows additional randomness due to a distribution of orientation of the oxygens in CggO. 

Sprik et al, 1993 Signorini et al, 1990), a typical example being the orientational disorder associated with NH in NH Br. Detailed simulations have been reported on (NaCN),, t(KCN),t and other mixed alkali halides and alkali cyanides. Other systems studied include potassium and calcium nitrate crystals and their mixtures. The transition from the crystalline to the superionic conductor phase in solid electrolytes has also been successfully investigated. Molecular dynamics studies of Agl were carried out by Parrinello, Rahman Vashishta (1983). LijSO has been investigated by molecular dynamics by Impey et al. (1985). Here, the Li ions become mobile at high temperatures. The ions exhibit orientational disorder and the orientational... 

This orientational disorder remains frozen in the crystalline lattice down to T — 0, leading to conspicuously nonzero S0 = 5.7 J mol-1 K-1. Similar well-documented cases of orientational disorder (and S0 0) are exhibited by N20 and many other species. 

Some compounds show meso-phases between the solid and liquid phases. These phases are classified into two kinds, namely liquid crystals in which the molecules have orientational order and disorganized position in one or more dimensions, and plastic crystal in which the molecules have organized positions and orientational disorder. Although the component ions in ILs are largely disordered, the appearance of liquid crystalline or plastic crystal phases could be the function of ion structures, when component ions have a tendency towards orientational or positional ordering by alignment of the ions and/or interaction among ions. Onium salt-type plastic crystals have been reported by MacFarlane [12,39]. 

Carbon tetrafluoride. Carbon tetra-fluoride, which undergoes a transition to a plastically crystalline (orientationally disordered) phase, has been investigated by the Parrinello-Rahman molecular dynamics method under constant-pressure conditions (6). A simple intermolecular potential model of the Lennard-Jones form was derived by taking into account the experimen-... 

Thus, although substitution generally increases the proportion of amorphous phase and leads to more disordered crystalline phases, the reverse effect can be obtained using specific molecular interactions between side groups and conjugated chains. This suggests that interaction of a CP chain with another, nonconjugated polymer could be used to orient the former. In a sense, this is what is achieved in blends (see Section II.E). 

J. Sherwood, The Plastically Crystalline State Orientationally Disordered Crystals, Wiley, 1979. 

The M3P11 phases transform into plastically crystalline modifications like the M3P7 phases. In the high-temperature form (/3), the phosphides match the structure of the intermetallic Li3Bi. The Bi positions are surrounded by the cages of P and Pn with orientational disorder. 

A molecule that appears to be orientationally disordered in the crystalline state is cyclohepta[ de jnaphthalene (pleiadiene), shown in Fig-... 

FCC phase was ascertained by the emergence of a set of crystalline Bragg peaks as described previously. Experimental results for the liquid phase are shown in Fig. la, as well as the total radial distribution function for the FCC phase (calculated as G(r) = 1 + Po (2ti) FT [S(q) - 1], where FT means Fourier Transform). For a description of data treatment see in this series the paper entitled Neutron diffraction as a tool to explore the free energy landscape in orientationally disordered phases or ref. ( ). 

Mixtures of clay platelets and polymer chains compose a colloidal system. Thus in the melt state, the propensity for the clay to be stably dispersed at the level of individual disks (an exfoliated clay dispersion) is dictated by clay, polymer, stabilizer, and compatibilizer potential interactions and the entropic effects of orientational disorder and confinement. An isometric dimension of clay platelets also has implications for stability because liquid crystalline phases may form. In addition, the very high melt viscosity of polypropylene and the colloidal size of clay imply slow particulate dynamics, thus equilibrium structures may be attained only very gradually. Agglomerated and networked clay structures may also lead to nonequilibrium behavior such as trapped states, aging, and glassy dynamics. 

The ordered positions of the norbornene units in the crystalline domains is shown in Fig. 23. It is apparent that the ball-like units are organized on a face centered-lattice. In this projection, only one of the possible ordered positions of the copolymer chain is shown. As also shown in Fig. 2IB, the ethylene units, which connect the norbornene units, may assume different positions along the a and b axes, producing orientational disorder of the chains and of the quasi-spherical norbornene units. However, the barycenter of the norbornene units remain organized on a face-centered lattice, producing the strong 111 reflection [121]. 

Sherwood N (1979) The plastically crystalline state (Orientationally disordered crystals). Wiley, Chichester... 

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