Mechanical Properties of СeF3 Single Crystals

Crystallography Reports - The anisotropy of the mechanical characteristics of CeF3 crystals (sp. gr. $$P\bar {3}c1$$) grown from the melt by the Bridgman technique has been studied for the first...     

Growth,Compositions, and Mechanical Characteristics of Sodium–Gadolinium Molybdate Single Crystals

Crystallography Reports - A concentration series of sodium–gadolinium molybdate single crystals have been grown by the Czochralski method from melts of stoichiometric and some...     

Analysis of γ-irradiated synthetic bone grafts by 29Si MAS-NMR spectroscopy,calorimetry and XRD

Ca–Sr–Zn–Si glasses have demonstrated excellent biocompatibility both in vitro using the MTT assay with L929 mouse fibroblast cells, and in vivo using healthy and ovariectomized female Wistar rats. However, the biological evaluation of the materials was performed on glass granules that were autoclaved, rather than γ-irradiated; the sterilisation procedure required prior to implantation of these materials in the human body. Given the fact that when a glass is exposed to ionizing radiation changes in its physical properties can take place, it is imperative to determine whether the structure of such glasses will be altered as a result of exposure to the typical amounts of γ-irradiation required to sterilise such materials prior to implantation. This paper examines the structure of Na–Ca–Sr–Zn–Si glasses using ²⁹Si MAS-NMR, XRD and DTA and to evaluate the effect of 30 kGy γ-irradiation on their structure. The ²⁹Si MAS-NMR results indicate that the peak maxima for each glass remains between ?74 ppm and ?79 ppm; a chemical shift for ²⁹Si associated with Q¹ units in silicate glasses, and that the local environment around the ²⁹Si isotope remains unaltered as a result of exposure. Additional analysis (DTA and XRD) showed that the onset of the glass transition temperature, T_g (in the range 553 °C–619 °C depending on composition) typically remains unchanged, as a result of exposure to the ionizing radiation, as do the XRD diffractograms for each glass. Therefore it can be concluded that the use of 30 kGy γ-irradiation does not effect the local environment of the ²⁹Si isotope in the glasses, nor does it significantly alter the XRD diffraction patterns or the T_g values for CaO–SrO–NaO–ZnO–SiO₂ described in this work.     

Pyroelectric Properties of Potassium and Rubidium Titanyl—Arsenate Single Crystals in the Temperature Range of 4.2–300 K

The temperature dependences of the pyroelectric coefficients of KTiOAsO₄ and RbTiOAsO₄ single crystals grown by flux crystallization have been investigated in the temperature range of 4.2–300 K. With an increase in temperature, superionic conductivity first arises in KTiOAsO4 (at T > 200 K) and then (at T > 270 K) in RbTiOAsO₄. This conductivity is much higher in the samples polarized at T = 4.2 K. An exponential change in the crystal resistivity along the polar direction is simultaneously observed. The results of measurements in the range of 4.2–200 K indicate larger values of pyroelectric coefficients when compared with potassium and rubidium titanyl-phosphate crystals. A correlation between the pyroelectric coefficients and a change in the lattice constants at isomorphic substitutions of K atoms for Rb and P atoms for As has been revealed within the symmetry approach.     

The Peculiarities of the Optical Absorption of Monocrystalline Fluorene and Its Heteroanalogues in the Energy Range Between 3.5 eV and 8.5 eV

Electronic absorption spectra of carbazole, dibenzofuran and fluorene were obtained in all three crystallographic directions (energy range 3.5-8.5eV). All electronic transitions with transition dipoles at oblique angles to a and b crystallographic axes can be traced to parental molecular states.

Crystal transitions with parallel transition dipoles can be traced to parental molecular states for thin (0.1-0.2μ) crystals, slow crystallized from melt under uniaxial pressure. For sublimation flakes and crystals fast crystallized from melt, these transitions cannot be traced to parental molecular states since their spectra have continuous, essentially uniform intensity distribution except for such transition at the onset of absorption.     

Temperature and Pressure Dependence Studies of the Motions of the +NH3 Radical Trapped in γ Irradiated Ammonium Perchlorate Single Crystal

The temperature and pressure dependences of the ⁺NH₃ coupling tensors have been investigated by ESR spectroscopy. The linear variation of the reduced correlation time of the “rotational diffusion” motion with reciprocal of the temperature is shown to be unrelated to the dilatation of the matrix. Comparison with ⁺ND₃ results gives the contribution to the nitrogen isotropic coupling constant of the out of plane vibration of the nitrogen atom.     

Study on the Local Structure Phase Transition, Spectral Fine Structure and EPR Spectra of RbCdF3∶Ni2+ Crystals

本文采用半自洽场(semi-SCF) 3d轨道模型和μ-K-α模型,利用完全对角化方法,建立了Oh、D4h对称晶体场局部结构参数与光谱精细结构、EPR谱之间的定量关系,统一解释了RbCdF3∶ Ni2晶体的光谱精细结构和EPR谱.所得理论结果与实验值符合很好.     

X-ray Topographic Investigation of Quartz Single Crystals at High Temperature,up to 1185°C

Real time experiments were performed to study the structural behaviour of monocrystalline quartz at high temperatures. White beam diffraction topography in transmission geometry was used. A creation of Dauphine-twins took place slightly below the α-β-phase transition temperature. The diffraction contrast of twins and temperature stresses disappeared above the α-β-phase transition temperature. Up to 1185°C neither changes of the defect structure nor a creation of new defects were observed. A precursor for a beginning of a reconstructive phase transition from quartz to cristabolite could not be observed within a time interval of 2h at 1180°C     

Exciton—Phonon Luminescence of Perfect and Doped Naphthalene Crystals

The structure of phonon side bands in luminescence spectra of local excitons is investigated both theoretically and experimentally. A gradual transition from a spectrum behaviour peculiar for deep impurity centers (with wide phonon side band) to that peculiar for low temperature intrinsic luminescence (the side band becomes split into several bands corresponding to long wave lattice phonons) is investigated depending on the local exciton level depth. Experimental investigations of deuteronaphthalene solutions are presented.     

Synthesis and crystal and molecular structure of newN-substituted γ-hydroxybutyramides

TheN-(2-phenylethyl)amide of-(1, 1-ethylenedioxy)-ethyl--hydroxybutyric acid (II) and theN-(p-methoxybenzyl)amide of-(1, 1-ethylenedioxy)-ethyl--hydroxybutyric acid (III) have been synthesized and the crystal structure ofIII has been solved. CompoundIII, C₁₆H₂₃O₅N, crystallizes in the monoclinic space groupP2₁/c witha=12.572(2),b=11.149(2),c=12.317(2) Å and=106.53(1)°. The structure was solved by direct methods, and refined by full-matrix least squares to giveR=0.040 (R _w =0.047) for 2004 intensities. The dioxolane ring has a deformed half-chair conformation.     

Editorial board page for “Journal of Molecular Crystals and Liquid Crystals”, Volume 60, Number 4

This is a scanned image of the original Editorial Board page(s) for this issue.     

Elastic and Optical Properties of Some 4′-n-Alkyl-4-Cyanobiphenyls

The bend elastic constants (k ₃₃) and order parameters (S) derived from optical measurements in the nematic phase of pentlyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) are reported. The odd-even effect is clearly seen in the K ₃₃ values of all four compounds and in the S values of the first three. 5CB, 6CB and 7CB show only the nematic mesophase but their elastic constants indicate the existence of smectic-like short range order. For example, even the lowest homologue, 5CB, does not obey the law k ₃₃ ∞ S ² given by the mean field throry. 7CB, has about the same order parameter as 5CB but a much higher elastic constant. 8CB, which shows a smectic A phase as well, exhibits a lower k ₃₃ than 7CB near the nematic-isotropic transition point but a pronounced pretransitional increase near the A-N transition.     

Editorial board page for “Journal of Molecular Crystals and Liquid Crystals”, Volume 84, Number 1-4

This is a scanned image of the original Editorial Board page(s) for this issue.     

Growth and Elemental Analysis of a Series of KTi1–xZr x OPO4 Crystals

Crystallography Reports - Crystals of the KTi1–xZr x OPO4 concentration series with a zirconium content y (in atomic fractions) in the melt ranging from 0 to 0.13 have been grown by the flux...     

Editorial board page for “Journal of Molecular Crystals and Liquid Crystals”, Volume 83, Number 1-4

This is a scanned image of the original Editorial Board page(s) for this issue.     

Observation of Ferromagnetic Domains in Nd?Fe?B Single Crystals by Photoelectron Microscopy

This paper reports on the successful growth of Nd Fe B single crystals. Ferromagnetic domains of these crystals are observed by photoelectron microscopy. Thc domains may disappear and re-appear during the experiments. A possible mechanism of the contrast formation of the domains is proposed and discussed.     

Synthesis and Crystal Structure of γ-Type Octamolybdates Coordinated by Alanines

Abstract  

The acidification of aqueous solutions containing Na₂MoO₄·2H₂O and KCl in the presence of alanine ligand gives an octamolybdate coordinated by two alanine ligands, K₄[Mo₈O₂₆(CH₃CH(NH₃)CO₂)₂]·4H₂O (1), which crystallizes with triclinic symmetry in the space group P[`1] P\overline{1} , the cell parameters being a = 9.0622(10) ?, b = 9.9652(11) ?, c = 10.6322(12) ?, α = 90.021(2)°, β = 100.656(2)°, γ = 106.271 (2)°, V = 904.42(17) ?³, Z = 1, D _c  = 2.920 g cm⁻³ and final R indices (I > 2σ(I)) R ₁ = 0.0257, wR ₂ = 0.0682, S = 1.115. The alanine ligands are coordinated via their carboxylate–oxygen as a monodentate ligand to γ-[Mo₈O₂₆]⁴⁻ anion.