Structural Specific Features of Solid Solutions NdxGd1 – xCr3(BO3)4

Optics and Spectroscopy - Optical investigations of crystals of solid solutions NdxGd1 – xCr3(BO3)4, 0.01 ≤ x ≤ 1, have been performed. Absorption spectra in the...     

Use of poly(ethylene terephthalate) track membranes as template matrices for the preparation of polymeric nanomaterials based on polypyrrole and poly(<Emphasis Type="Italic">N</Emphasis>-methylpyrrole)

The oxidative polymerization of pyrrole and N-methylpyrrole with the use of template synthesis on poly(ethylene terephthalate) (PET) track membranes was studied. By scanning electron microscopy (SEM), it was found that a polymer film was formed on the surface of membranes and on the walls of membrane pores. The rates of polymerization on the surface of membranes and pore walls, as well as the yield and structure of the polymer film, depend on the membrane parameters (pore length and diameter and membrane porosity), the chemical structure of the monomer, the diffusion of polymerized solutions through template pores, and the temperature.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 1, 2005, pp. 15–20.Original Russian Text Copyright © 2005 by Dobretsova, Ermolaev, Jitariouk, Milinchuk.     

Ultrasound synthesis of diaryl ethers

Russian Chemical Bulletin - 2,2-Bis[4-(4-nitroaryl)phenyl]hexafluoropropanes appropriate for the synthesis of monomers were prepared by the reaction of 2,2-bis[4-hydroxyphenyl)hexafluoropropane...     

Mobility of Dirac electrons in HgTe quantum wells

The mobility of Dirac electrons (DEs) in HgTe quantum wells with the thickness close to the critical value corresponding to the transition from the direct to inverted spectrum has been studied experimentally and theoretically. The nonmonotonic dependence of this mobility on the electron density is found experimentally. The theory of DE scattering on impurities and fluctuations of the thickness of a well caused by its roughnesses is elaborated. This theory is in good agreement with experiment and explains the observed nonmonotonicity by the decrease in the ratio of the de Broglie wavelength of DEs to the characteristic size of the roughness with the increase in their concentration.     

Infrared spectroscopy of europium borates Eu<Emphasis Type="Italic">M</Emphasis><Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Al,Cr, Fe,Ga) with a huntite mineral type of structure

Huntite-like EuM ₃(BO₃)₄ crystals (M = Al, Cr, Fe, or Ga) are synthesized by means of spontaneous crystallization from a solution in a melt. The infrared spectra of the compounds are measured. The experimental data and the results from ab initio DFT calculations are compared. The comparison shows that the compounds have a primarily noncentrosymmetric rhomboherdal structure with the R32 space group. This indicates these compounds could exhibit magnetoelectric and nonlinear optical properties.     

IR spectroscopy of rare-earth aluminum borates RAl3(BO3)4 (R = Y,Pr-Yb)

Rare-earth aluminum borates RAl₃(BO₃)₄ (R = Y, Nd-Yb) obtained by spontaneous high-temperature flux crystallization form two polytype modifications described by the space groups R32 (D ₃ ⁷ ) and C2/c (C _2h ⁶ ). They differ in the symmetry versions in mutual arrangement of layers. These borates have been investigated by mid- and far-IR spectroscopy in combination with factor-group analysis of the vibrations of BO ₃ ^3? ions; translational motions of Al³⁺, R³⁺ (Y, Nd-Yb), and BO ₃ ^3? ions; and BO ₃ ^3? rotations. Rare-earth aluminum borates are assigned to different space groups according to their IR spectra. Borates with large rare-earth Nd and Pr cations are crystallized into the space group C2/c (C _2h ⁶ ), while borates with smaller (Y, Sm-Yb) ions are crystallized into the space group R32 (D ₃ ⁷ ). The rhombohedral structure of the latter compounds includes monoclinically ordered domains, as is evidenced by the presence of monoclinic-phase bands in the IR spectrum. NdAl₃(BO₃)₄ and SmAl₃(BO₃)₄ can form both monoclinic and rhombohedral polytypes. The IR spectrum of the monoclinic SmAl₃(BO₃)₄ phase contains bands due to the rhombohedral phase, while the IR spectrum of NdAl₃(BO₃)₄ (which is described by the space group R32) contains bands due to the monoclinic polytype. The presence of domains with another arrangement of layers in the polytype structure is a characteristic sign that corresponds to the order-disorder theory; this theory explains the structure of polytypes.     

Formation of Germanium–Vacancy Color Centers in CVD Diamond

We study Ge-doped polycrystalline diamond films synthesized, using microwave plasma chemical vapor deposition (CVD) in CH₄-H₂ base mixtures. We compare two sources of the dopant – gaseous monogermane (GeH₄) and solid Ge plates. We investigate the structure and phase composition of the obtained films, using scanning electron microscopy, photoluminescence (PL), and Raman spectroscopy. We vary the precursor gas composition to maximize the intensity of the Germanium–vacancy (Ge-V) PL signal at 602 nm and discover that, using [C]-rich gas mixtures ([CH₄]=20%), we are able to increase the intensity of Ge-V signal by two orders of magnitude in comparison with Ge-doped high-quality microcrystalline films of the same thickness but grown at [CH₄]=4%. The attained results may be used for the fabrication of polycrystalline diamond films and plates with high concentrations of Ge-V centers, which may serve as source material for the fabrication of submicrometer-sized luminescent diamond particles for local optical thermometry.

     

Unexpected formation of the most strained δ-lactone in the pyrolysis of diethyl ester of cis-4-hydroxy-trans-5-methoxy-trans-1,2-cyclohexanedicarboxylic acid

Vacuum distillation of diethyl ester of cis-4-hydroxy-trans-5-methoxy-trans-1,2-cyclohexanedicarboxylic acid gave a single compound, 5-ethoxycarbonyl-7-methoxy-2-oxa[2.2.2.]bicyclooctan-3-one. The structure of this -lactone was demonstrated by data of NMR and IR spectroscopy. Calculations using the method of molecular mechanics showed that this structure has the highest steric strains of all possible stereoisomeric -lactones.M. V. Lomonosov Moscow State University, Moscow 119899. M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow 117571. K. D. Ushinskii Yaroslavl' State Pedagogical University, Yaroslavl' 150000. Translated from Khimiya Geterotsiklicheskaya Soedinenii, No. 1, pp. 41–47, January, 1997.