			Home About us Contact

Mixed Crystals (mixed + crystal)

Distribution by Scientific Domains

Physics and Astronomy	58%
Chemistry	35%

Selected Abstracts

Mixed Crystals in the System Cu3Mo2O9/Zn3Mo2 O9.

CHEMINFORM, Issue 20 2005
Werner Reichelt
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Mixed crystal of bis(,2 -N,N-di-n-butyldithiocarbamato-S,S,S,)-bis(N,N-di-n-butyldithiocarbamato-S,S,)-di-zinc(II) and bis(,2 -N,N-di-n-butyldithiopercarbamato-S,O,O,)-bis(N,N-di-n-butyldithiocarbamato-S,S,)-di-zinc(II)

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007
F. Emmerling
Abstract The title compounds Zn2[S2CN(n-C4H9)2]41 and Zn2[(S(SO)CN(n-C4H9)2)(S2CN(n-C4H9)2)]23 build mixed crystals in the ratio 0.42: 0.58. Each compound forms dimers, in which the monomer moieties are related via a two-fold axis, coinciding with that of the monoclinic space group C2/c. The lattice parameters are a = 23.581(9), b = 17.112(5), c = 16.372(9) Å, and , = 128.33(3)°. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hetero-Seeding and Solid Mixture to Obtain New Crystalline Forms

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009
Dario Braga Prof.
Abstract Para -methyl benzyl alcohol (p -MeBA,II) and para -chloro benzyl alcohol (p -ClBA) are quasi-isostructural and share the same hydrogen-bond patterns, but their crystals are not isomorphous. No new polymorphs could be obtained by conventional polymorph screening based on different solvents and different crystallization conditions. Formation of a new polymorph of p -MeBA named p -MeBA,I, isomorphous with the crystal of p -ClBA, was induced by hetero-seeding with a small quantity of powdered p -ClBA added to a supersaturated solution of p -MeBA in hexane, while seeding of p -ClBA with p -MeBA,II failed to give a new phase of p -ClBA isomorphous with known crystalline p -MeBA,II. Mixed crystals of p -MeBA and p -ClBA were also prepared with different p -MeBA/p -ClBA ratios to understand the role of the different functional groups in the crystal structure. Crystal phases were characterized by combined use of single-crystal and powder X-ray diffraction, differential scanning calorimetry, and solid-state NMR spectroscopy. [source]

Investigation of thermal conductivity of nitride mixed crystals and superlattices by molecular dynamics

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
Takahiro Kawamura
Abstract The thermal conductivities of AlxGa1,xN and InxGa1,xN mixed crystal and AlN/GaN superlattices were investigated by molecular dynamics simulation. We used Stillinger-Weber potentials, and Green-Kubo's formula was employed to calculate thermal conductivity. The results showed that the value of thermal conductivity of Al0.5Ga0.5N was about 1/20 smaller than that of GaN. It was also found that the thermal conductivity of AlN/GaN superlattices along the c-axis, which is parallel to the growth direction, was much less than that of bulk GaN. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Preferential enrichment: Full crystallographic analysis of the unusual phenomenon in the mixed crystals' version

CHIRALITY, Issue 7 2002
Hiroki Takahashi
Abstract Full characterization of the crystal structures of the racemate, nonracemate (20% ee), and pure enantiomer of [2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]trimethylammonium p -bromobenzenesulfonate (NBMe3), which has successfully shown an unusual enantiomeric resolution phenomenon, "preferential enrichment," was achieved by means of X-ray crystallographic analysis and construction of the binary melting point phase diagram. The crystalline nature of the racemate is not a racemic compound but a fairly ordered mixed crystal composed of the two enantiomers. The crystal structure of the nonracemate (20% ee) is virtually identical with that of the racemate and similar to that of the pure enantiomer. The binary melting point phase diagram of NBMe3 is consistent with the nature of a mixed crystal composed of the two enantiomers. Chirality 14:541,547, 2002. © 2002 Wiley-Liss, Inc. [source]

Epitaxial Sn1-xPbxS nanorods on iso-compositional thin films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2010
K. Bente
Abstract Based on SnS (Herzenbergite) , SnPbS2 (Teallite) mixed crystals with orthorhombic layer structures, thin films and lawns of Sn1-xPbxS nanorods were produced using hot wall vacuum deposition method (HWVD). The lawn was formed onto the surface of an underlying thin Sn1-xPbxS film which is build by differently oriented blocks. The density of rods arranged like a lawn depends on the metal ratio and substrate temperature. X-ray and TEM analysis of the epitaxial material showed preferential (001) orientation perpendicular to the surface of the glass substrate. The roughness of the films measured by atomic force microscopy was in the range of Rq = 49.5,86.3 nm depending on lead concentration The rods were about 500 nm high and 300 nm in diameter. As revealed by TEM-EDX experiments the droplet at the tip of rods consists of tin. Therefore it is assumed the rods grew via a self-consuming vapor,liquid,solid (VLS) mechanism. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1-x) mixed crystals (0.25 , x , 1)

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010
N. M. Gasanly
Abstract The optical properties of the TlInS2xSe2(1-x)mixed crystals (0.25 , x , 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400,1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS2xSe2(1-x)mixed crystals. The transmission measurements carried out in the temperature range of 10,300 K revealed that the rates of change of the indirect band gaps with temperature are , = ,9.2×10,4 eV/K, ,6.1×10,4 eV/K, ,4.7×10,4 eV/K and ,5.6×10,4 eV/K for TlInS2, TlInS1.5Se0.5, TlInSSe and TlInS0.5Se1.5 crystals, respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Studies on multiphased mixed crystals of NaCl, KCl and KI

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2009
M. Priya
Abstract Multiphased mixed crystals of NaCl, KCl and KI were grown by the melt method, for the first time. Densities and refractive indices of all the grown crystals were determined and used for the estimation of the composition in the crystal. Atomic absorption spectroscopic measurements were done to estimate the metal atom contents in the crystal. Lattice parameters and thermal parameters (Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency) were determined from the X-ray powder diffraction data. DC and AC electrical measurements were done at various temperatures ranging from 40 to 150°C. Activation energies were also estimated. The observed lattice parameters showed that the system exhibits three phases each nearly corresponds to NaCl, KCl and KI. The thermal and electrical parameters show a highly nonlinear bulk composition dependence. Results are reported. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mixed crystal of bis(,2 -N,N-di-n-butyldithiocarbamato-S,S,S,)-bis(N,N-di-n-butyldithiocarbamato-S,S,)-di-zinc(II) and bis(,2 -N,N-di-n-butyldithiopercarbamato-S,O,O,)-bis(N,N-di-n-butyldithiocarbamato-S,S,)-di-zinc(II)

Control of apatite crystal growth by the co-operative effect of a recombinant porcine amelogenin and fluoride

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 2006
Mayumi Iijima
Recently, we used native amelogenins extracted from developing pig enamel to examine the combined effect of fluoride and amelogenins on the growth of octacalcium phosphate (OCP) and apatite crystals. The purpose of the present study was to investigate this combined effect using a highly purified recombinant amelogenin. We applied porcine amelogenin (rP172) and fluoride in a dual-membrane system as a model for tooth enamel formation. The combination of rP172 and fluoride in this system resulted in the formation of rod-like apatite crystals. On the other hand, without fluoride, rod-like OCP crystals of a comparable size were formed, and rather large hexagonal prisms of mixed crystals of OCP and apatite grew without amelogenins. Thus, highly purified and homogeneous recombinant amelogenin, in co-operation with F, regulated the mineral phase, habit, and size of crystals in the same manner as the extracted heterogeneous porcine amelogenins. We suggest that in both cases the control over the crystal phase and morphology was a direct effect of amelogenin protein serving as a scaffold for apatite mineralization. [source]

Mechanism of Selective and Unselective Enclathration by a Host Compound Possessing Open, Flexible Host Frameworks

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2003
Kazunori Nakano
Abstract Molecular recognition of o -, m -, and p -xylenes (oX, mX, and pX) through enclathration of cholic acid (CA) is described. All of the xylenes give lattice inclusion crystals with CA, and crystallographic studies reveal that they are included in different open host frameworks. In particular, oX has two polymorphs, depending on the recrystallization temperatures. Competitive recrystallization from mixtures of xylenes resulted in selective enclathrations and the formation of racemic mixed crystals. In the presence of an equimolar amount of oX, CA selectively includes mX or pX in the host frameworks, which are identical to those obtained from the pure mX or pX, respectively. The low affinity of oX is explained in terms of a lower stability of CA·oX than of the other two complexes, as judged from the low PCcavity, the volume ratio of the guest compound to the host cavity. Meanwhile, mixtures of mX and pX yield inclusion crystals that accommodate both of the guests. These have the same open host framework as obtained from pure mX, and the guest components are disordered statically in the host cavity. The ratios of the xylene mixtures in the single crystals are similar to those in the original recrystallization mixtures, and also in the bulk crystals, indicating that CA forms mixed crystals of mX and pX. This non-selectivity is attributed to the similar stabilities of CA·mX and CA·pX, according to the moderate PCcavity. The inclusion behavior of CA from mixtures of xylenes is quite similar to chiral recognition by diastereomer-salt methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Polymorphism of racemic felodipine and the unusual series of solid solutions in the binary system of its enantiomers

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2001
Judith M. Rollinger
Abstract The aim of this study was to investigate the binary phase diagram and the polymorphism and pseudopolymorphism of racemic and enantiomeric felodipine, including their spectroscopic and thermodynamic properties. Different crystal forms were obtained by crystallization from solvents or from the annealed melt and investigated by thermal analysis (hot stage microscopy, differential scanning calorimetry, thermogravimetric analysis), spectroscopic methods (Fourier transform infrared,and Fourier transform,Raman spectroscopy), and X-ray powder diffractometry. The binary melting phase diagram was constructed based on thermoanalytical investigations of quantitative mixtures of (+)- and (±)-felodipine. Two polymorphic forms of racemic felodipine, mod. I (mp, ,145°C) and mod. II (mp, ,135°C), as well as an acetone solvate (SAc,) were characterized. Melting equilibria of felodipine crystal forms decrease due to thermal decomposition. Enantiomeric felodipine was found to be dimorphic (En-mod. I: mp, ,144°C; En-mod. II: mp, ,133°C). Evaluation of the binary system of (+)- and (,)-felodipine results in the formation of a continuous series of mixed crystals between the thermodynamically stable and higher melting modifications, mod. I and En-mod. I. Their unusual curve course, termed as Roozeboom Type 2 b, passes through a maximum in the racemic mixture and is flanked by a minimum at 20% and at 80% (+)-felodipine. From the thermodynamic parameters, racemic mod. I and II are monotropically related. In contrast to SAc, the thermodynamically unstable mod. II shows a considerable kinetic stability. Because its crystallization is badly reproducible, the use of mod. II is not advisable for processing. However, desolvation of SAc leads to a profitable crystal shape of mod. I, representing a pseudoracemate by definition. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:949,959, 2001 [source]

Isotope and disorder effects in the Raman spectra of LiHxD1,x crystals

JOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2001
V. G. Plekhanov
Most of the physical properties of a solid depend on its isotopic composition in some way or another. Scientific interest, technological promise and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled crystals. A great number of stable isotopes and well-developed methods for their separation have made it possible to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu2O, Si, Ge and ,-Sn with a controllable isotopic composition. Among these compounds, LiH possesses the largest value of the isotope effect. The great number of theoretical and experimental data suggest that the isotopic composition of a crystal lattice exerts some influence on the vibrational properties of crystals. These effects are fairly large and can be readily measured by modern experimental techniques (ultrasound, Brillouin and Raman scattering and neutron scattering). In addition, crystals of different isotopic compositions possess different Debye temperatures. This difference between an LiH crystal and its deuterated analogue exceeds a 100 K. Very pronounced and general effects of isotopic substitution are observed in phonon spectra. The scattering lines in isotopically mixed crystals are not only shifted (the shift of LO lines exceeds 100 cm,1) but are also broadened. This broadening is related to the isotopic disorder of the crystal lattice. It is shown that the degree of a change in the scattering potential is different for different isotopic mixed crystals. In the case of germanium and diamond crystals, phonon scattering is weak, which allows one to apply successfully the coherent potential approximation (CPA) for describing the shift and broadening of scattering lines. In the case of lithium hydride, the change in the scattering potential is so strong that it results in phonon localization, which is directly observed in experiments. The common nature of the isotopic and disorder effects in a wide range of crystals is emphasized. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Investigation of thermal conductivity of nitride mixed crystals and superlattices by molecular dynamics

Mixed coordination and time-resolved luminescence of lead impurity centres

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
K. Polák
Abstract The optical properties of Pb2+ -doped K(Cl,Br) and K(Cl,I) mixed crystals were investigated to learn how a mixed surroundings influence mainly emission characteristics of lead impurity centres. In the first case, the emission spectrum changes step-by-step from the chloride to the bromide limit while corresponding lifetimes show some new features. In the second case, the continuity is affected by very low solid-state solubility and a strong tendency to foreign phase creation in stored crystals was observed. Nevertheless, some evidence of mixed lead coordination was found. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]