Physico-chemical properties of pure and x-ray irradiated single crystals of KAP

Single crystals of potassium hydrogen phthalate (KAP) have been grown by slow evaporation method from aqueous solutions. Thermal analyses indicate that KAP crystals decompose into phthalic anhydride and KOH around 520 K. Electrical properties of single crystals of KAP have been studied along with the effect of X-ray irradiation of the crystals. The electrical transport appears to be associated with tunneling of protons. The irradiated crystal exhibits lower dielectric constant and higher ac conductivity.

Spectral assignments based on the 13C NMR spectra of mixed liquid crystals of opposite diamagnetic anisotropies

The proton-decoupled 13C NMR spectra of mixtures of liquid crystals with opposite diamagnetic anisotropies have been studied in the natural abundance of 13C. A new method to assign the spectral lines to specific carbons in the liquid crystalline phase has been developed. For this purpose, the assignments of lines in the isotropic media are required, and they were obtained from two-dimensional hetero-COSY experiments. From the spectra in the �critical� mixtures where both the orientations of the liquid crystal directors, with the alignments along and perpendicular to the direction of the magnetic field, �coexist,� the 13C chemical-shift anisotropies have been determined, assuming uniaxial symmetry.

Crystallization and Preliminary X-ray Diffraction Analysis of Crystals of Thermoascus aurantiacus Xylanase

Crystals suitable for high resolution X-ray diffraction analysis have been grown of the 29,774-Da protein, xylanase (1,-4-beta-xylan xylanohydrolase EC 3.2.1.8) from the thermophilic fungus Thermoascus aurantiacus. This protein, an endoxylanase demonstrates the hydrolysis of β-(1-4)-Image -xylose linkage in xylans and crystallizes as monoclinic pinacoids in the presence of ammonium sulphate buffered at pH 6·5, and also with neutral polyethylene glycol 6000. The crystals belong to space group P 21 and have cell dimensions, a = 41·2 Å, b = 67·76 Å, c = 51·8 Å; β = 113·2°.

Structural phase transitions in Bi2V1-xGexO5.5-x/2 (x=0.2, 0.4, and 0.6) single crystals: X-ray crystallographic study

Single crystals of Bi2V1-xGexO5.5-x/2 (x = 0.2, 0.4, and 0.6) were grown by slow cooling of melts. Bismuth vanadate transforms from an orthorhombic to a tetragonal structure and subsequently to an orthorhombic system when the Ge4+ concentration was varied from x = 0.2 to x = 0.6. All of these compositions crystallized in polar space groups (Aba2, F4mm, and Fmm2 for x = 0.2, 0.4, and 0.6, respectively). The structures were fully determined by single crystal X-ray diffraction studies, (C) 1999 Elsevier Science Ltd.

Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1-x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x = .05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Transport, optical and magnetotransport properties of hetero-epitaxial InAsxSb1−x/GaAs(x0.06) and bulk View the MathML source crystals: experiment and theoretical analysis

We briefly review the growth and structural properties of View the MathML source bulk single crystals and View the MathML source epitaxial films grown on semi-insulating GaAs substrates. Temperature-dependent transport measurements on these samples are then correlated with the information obtained from structural (XRD, TEM, SEM) and optical (FTIR absorption) investigations. The temperature dependence of mobility and the Hall coefficient are theoretically modelled by exactly solving the linearized Boltzmann transport equation by inversion of the collision matrix and the relative role of various scattering mechanisms in limiting the low temperature and View the MathML source mobility is estimated. Finally, the first observation of Shubnikov oscillations in InAsSb is discussed.

Hydrothermal growth and characterization of ZnO crystals

ZnO crystals with dimensions of 30 x 38 x 8 turn 3 have been grown by the hydrothermal method using a mixed solution of KOH, LiOH and H2O2. The growing rates for +c(0001) and -c(000 (1) over bar) were 0.17 and 0.09 mm/day, respectively. The crystal color was very light green for +c sector and dark brown for -c sector. For the +c sector, the resistivity at room temperature was 80 0 cm, the carrier concentration was about 10(4)/cm(3), and the mobility was about 100 cm(2)/Vs. The full-width at half-maximum (FWHM) of double axis X-ray rocking curve for the polished Zn face cut from +c sector was 45 arcsec. The photoluminescence (PL) spectrum and the absorption spectrum of +c part of the crystals at room temperature were also reported and discussed in this paper. (c) 2008 Elsevier B.V. All rights reserved.

Comparison between double crystals X-ray diffraction micro-Raman measurement on composition determination of high Ge content Si1_xGex layer epitaxied on Si substrate

It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction (DCXRD) and micro-Raman measurement, were introduced comparatively to determine x value in Si1-xGex: layer, which show that while the two methods are consistent with each other when x is low, the results obtained from double crystals X-ray diffraction are not credible due to the large strain relaxation occurring in Si1-xGex layers when Ge content is higher than about 20%. Micro-Raman measurement is more appropriate for determining high Ge content than DCXRD.

Perovskite-Like Mixed Oxides (LaSrMn1-x Ni (x) O4+delta, 0 a parts per thousand currency sign x a parts per thousand currency sign 1) as Catalyst for Catalytic NO Decomposition: TPD and TPR Studies

Catalytic NO decomposition on LaSrMn1-x Ni (x) O4+delta (0 a parts per thousand currency sign x a parts per thousand currency sign 1) is investigated. The activity of NO decomposition increases dramatically after the substitution of Ni for Mn, but decreases when Mn is completely replaced by Ni (x = 1.0). The optimum value is at x = 0.8. These indicate that the catalytic performance of the samples is contributed by the synergistic effect of Mn and Ni. O-2-TPD and H-2-TPR experiments are carried out to explain the change of activity. The former indicates that only when oxygen vacancy is created, could the catalyst show enhanced activity for NO decomposition; the latter suggests that the best activity is obtained from catalyst with the most matched redox potentials (in this work, the biggest Delta T and Delta E values).

Tunable photonic crystals by mixed liquids

Tunable photonic crystals were prepared by infiltrating mixed liquids into the voids of silica opals. The stop bands of the tunable photonic crystals were continuously tuned by changing the relative refraction index contrast n(mix)/ns(pheres) of the spheres and the mixed liquids by varying the volume fraction of the component of the mixed liquids. The peak wavelengths of the stop band have a red shift as the refractive index of the mixed liquids increases. The transmittance at the stop band decreases with the increase of the refractive index contrast n(mix)/n(spheres). The larger the diameter of silica opals is, the wider the tunable range of the stop band is. The position and transmittance of the peak wavelength obtained by the photonic band calculations agreed very well with the experimental data.

Local similarity in organic crystals and the non-uniqueness of X-ray powder patterns

Two new concepts for molecular solids, 'local similarity' and 'boundary-preserving isometry', are defined mathematically and a theorem which relates these concepts is formulated. 'Locally similar' solids possess an identical short-range structure and a 'boundary-preserving isometry' is a new mathematical operation on a finite region of a solid that transforms mathematically a given solid to a locally similar one. It is shown further that the existence of such a 'boundary-preserving isometry' in a given solid has infinitely many 'locally similar' solids as a consequence. Chemical implications, referring to the similarity of X-ray powder patterns and patent registration, are discussed as well. These theoretical concepts, which are first introduced in a schematic manner, are proved to exist in nature by the elucidation of the crystal structure of some diketopyrrolopyrrole (DPP) derivatives with surprisingly similar powder patterns. Although the available powder patterns were not indexable, the underlying crystals could be elucidated by using the new technique of ab initio prediction of possible polymorphs and a subsequent Rietveld refinement. Further ab initio packing calculations on other molecules reveal that 'local crystal similarity' is not restricted to DPP derivatives and should also be exhibited by other molecules such as quinacridones. The 'boundary-preserving isometry' is presented as a predictive tool for crystal engineering purposes and attempts to detect it in crystals of the Cambridge Structural Database (CSD) are reported.

Studies on the energy band structures and chemical bond properties of LaX(X=N, P, As, Sb) crystals

The energy band structures of LaX(X=N, P, As, Sb) crystals have been studied by using LMTO-ASA method. The calculated energy gaps of these crystals are 2. 30 eV for LaN, 2. 05 eV for LaP, 1. 66 eV for LaAs and 1. 34 eV for LaSb. The results are in good agreement with experimental data, At the same time, using these calculated results of energy band structures of these crystals, the chemical bond properties have been analyzed and calculated, The covalency values of these crystals are 26.15% for LaN, 32.54% for LaP, 33.30% for LaAs and 36.49% for LaSb, which agree satisfactorily with the calculated ones by using PV (Phillips-Vechten) theory.