Single-crystal phase transition studie

A single-to-single crystal phase transition was found to take place at 333 K in a new polymorph of ort/zo-ethoxy-trans-cinnamic acid [77]. In this study, the structures of the title compound obtained at two temperatures above the transition point were determined in addition to the structures of the stabilized forms existing at lower temperatures. It was found that the phase transition involved a cooperative conformational transformation coupled with a shift in layers of the constituent molecules. 

Squaric acid 4,4 -Bipyridine Structure and characterization of the 1 1 cocrystal, and study of the single-crystal to single-crystal phase transition around 175 °C [50]... 

X-ray scattering structural studies of very small single crystals, phase transition in powders, local order in amorphous solids, glasses. . . ... 

This means, for example, the study of the three dimensional order on very small single crystals, phase transitions or transformations under physical or chemical factors of crystalline powders but also vitreous transition of glasses, large angle and small angle X-ray scattering (LAXS—SAXS) of amorphous phases, liquids or coordination complexes in solution. 

Zhang M, Salje EKH, Bismayer U (1996) Structural phase transition near 825 K in titanite evidence from infrared spectroscopic observation. Am Mineral 82 30-35 Zhang M, Meyer H-W, Groat LA, Bismayer U, Salje EKH, Adiwidjaja G (1999) An infrared spectroscopic and single-crystal X-ray study of m ayaite, CaSnSiOs. Phys Chem Miner 26 546-553... 

Section 4 is entirely devoted to ferroelectric and H-bonded systems. It also provides a nice illustration of results that always maintained the utility of proton NMR in solid state, even wideline, or how the old question of the order disorder or displacive nature of some ferroelectric phase transitions were reopened by progresses in NMR resolution. A number of structural phase transition is discontinuous, but the examples of coexistence in solid-state and kinetic studies are rather scarce this is the object of Section 5. Section 6 is devoted to single-crystal studies that allow very precise comprehension of subtle phase transition mechanisms. Section 7 introduces the salient features of NQR that represent an interesting alternative to NMR in some cases. The section ends with a table of miscellaneous phase transitions that complete the references given in the text. Section 8 concludes and presents some perspectives in NMR phase transition studies. 

The current knowledge of the CO + O2 reaction mechanism makes possible to state rather justified theoretical models giving insight to the features of spatio-temporal dynamics of reaction on the platinum surface. Carbon monoxide oxidation over Pt(lOO) single crystal has been studied comprehensively. It was shown that under certain conditions (partial pressures of reactants and temperature), the adsorbate coverages and the reaction rate undergo self-oscillations attended by the spatio-temporal pattern of COads and Oads formation on the surface [1,2,94]. The observed phenomena are associated with the reversible adsorbate-induced surface phase transition hex 1 X 1. The platinum state in unreconstructed 1x1 phase is catalytically active due to the ease of oxygen molecules dissociation S (02) 0.3—0.4 S (02) 10. The CO... 

Rare gas solids can be considered as the simplest nonmetal systems. However, the high pressure polymorphism in solid helium is surprisingly complex for a simple system. Helium crystallizes only under pressure in a/cc structure and has a small range of stability of a bcc structure near 3 x 10 GPa and 1.5 K. X-ray diffraction measurement showed that He crystallizes at 11.5 GPa and 298 K in a hep structure. This modification is the only solid phase observed at room temperature to 23 GPa. Single-crystal X-ray studies of Ne and Ar showed the stability of the fee phases of these elements up to 110 and 80GPa, respectively [37, 38]. However, in Ar at P > 50 GPa a hep modification appears and its concentration increases as pressure grows the fee hep transition completes at P 300 GPa. Kr starts a similar transition at 3.2 and completes it at ea. 170 GPa. Xe also starts a fee hep transformation... 

Solid-State Studies Phase Transitions and Thermochromism 3.11.5.3.1 Single crystal X-ray crystallography... 

Most polymers do not form crystals suitable for single crystal X-ray diffraction, so powder or film methods are usually employed. X-ray and LJV data recorded at various temperatures provide the detailed information required to correlate conformational and electronic properties, since the former is sensitive to the inter- and intrachain packing, and the latter is sensitive to the conformation. DSC provides further evidence for any phase transitions. Detailed studies have been performed by Winokur and West,260 261 who reported a comparison of the polymorphism, structure, and chromism in poly(di- -octylsilylene), (Si- -Oct2), 89, and poly(di- -dccylsilylcnc)(Si- -Dcc2) , 90. These investigations will be described in detail for the useful insights into polysilane structures that they afford. 

It is noteworthy that prior to the advent of scanning probe microscopy electrochemically driven reconstruction phenomena had been identified and studied using traditional macroscopic electrochemical measurements [210,211], However, STM studies have provided insight as to the various atomistic processes involved in the phase transition between the reconstructed and unreconstructed state and promise to provide an understanding of the macroscopically observed kinetics. An excellent example is provided by the structural evolution of the Au(lOO) surface as a function of potential and sample history [210,211,216-223], Flame annealing of a freshly elec-tropolished surface results in the thermally induced formation of a dense hexagonal close-packed reconstructed phase referred to as Au(100)-(hex). For carefully annealed crystals a single domain of the reconstructed phase... 

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