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Crystal Composition (crystal + composition)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Growth and characterization of LiCaGaF6

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005
E. Sani
Abstract Optically clear LiCaGaF6 (LiCGaF) single crystals up to 15 mm length were grown by the Czochralski method from CaF2 deficient melts. The substance melts incongruently at 751 °C. No significant deviations of the crystal composition from the nominal stoichiometry Li:Ca:Ga=1:1:1 could be found. X-ray structure analysis revealed that the substance crystallizes in the colquiriite type structure. LiCaGaF6 is transparent for optical wavelengths >140 , 150 nm. The thermal expansion of the trigonal crystals is ,11 = ,22 = 18.7×10 -6 K -1 perpendicular [001] and ,33 = 2.7×10 -6 K -1 parallel [001]. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-ray absorption by macromolecular crystals: the effects of wavelength and crystal composition on absorbed dose

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2004
James W. Murray
Radiation damage restricts the useful lifetime for macromolecular crystals in the X-ray beam, even at cryotemperatures. With the development of structural genomics pipelines, it will be essential to incorporate projected crystal lifetime information into the automated data collection software routines. As a first step towards this goal, a computer program, RADDOSE, is presented which is designed for use by crystallographers in optimizing the amount of data that can be obtained from a particular cryo-cooled crystal at synchrotron beamlines. The program uses the composition of the crystal and buffer constituents, as well as the beam energy, flux and dimensions, to compute the absorption coefficients and hence the theoretical time taken to reach an absorbed dose of 2,×,,Gy, the so-called `Henderson limit'. At this dose, the intensity of the diffraction pattern is predicted to be halved. A `diffraction,dose efficiency' quantity is introduced, for the convenient comparison of absorbed dose per diffracted photon for different crystals. Four example cases are considered, and the implications for anomalous data collection are discussed in the light of the results from RADDOSE. [source]

Composition dependence of the OH-stretch-mode spectrum in lithium tantalate

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2004
C. Bäumer
Abstract The infrared absorption spectrum of the OH-stretch-mode in lithium tantalate is measured for crystals of different compositions. The spectrum exhibits two prominent lines which are representative for ideal and for Li-deficient sites in the crystal, respectively. Position, shape, and intensity of the two lines thus depend on crystal composition in a characteristic way. A comprehensive quantitative description is given which shows that the technique can be used as a sensitive non-destructive tool to rate the composition of lithium niobate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photoswitchable Gas Permeation Membranes Based on Liquid Crystals

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Eric G, owacki
Abstract We have fabricated switchable gas permeation membranes in which a photoswitchable low-molecular-weight liquid crystalline (LC) material acts as the active element. Liquid crystal mixtures are doped with mesogenic azo dyes and infused into commercially available track-etched membranes with regular cylindrical pores (0.40 to 10.0 ,m). Tunability of mass transfer can be achieved through a combination of (1) LC/mesogenic dye composition, (2) surface-induced alignment, and (3) reversible photoinduced LC-isotropic transitions. Photo-induced isothermal phase changes in the imbibed material afford large and fully reversible changes in the permeability of the membrane to nitrogen. Both the LC and photogenerated isotropic states demonstrate a linear permeability/pressure relationship, but they show significant differences in their permeability coefficients. Liquid crystal compositions can be chosen such that the LC phase is more permeable than the isotropic,or vice versa , and can be further tuned by surface alignment. Permeability switching response times are 5 s, with alternating UV and >420-nm radiation at an intensity of 2 mW/cm2 being sufficient for complete and reversible switching. Thermal and kinetic properties of the confined LC materials are evaluated and correlated with the observed permeation properties. We demonstrate for the first time reversible permeation control of a membrane with light irradiation. [source]