Influence of Shear Deformation on Carbon Onions Stability under High Pressure

The influence of shear deformation on carbon onions stability under high pressure up to 45 GPa was investigated in a Shear Diamond Anvil Cell (SDAC) by the Raman spectroscopy and the Transmission Electron Microscopy (TEM). At shear less then 40 degrees the carbon onions are stable up to 30 GPa. Biger shear deformation leads to increasing of size and destruction of the onions and to formation of sp3 C-C bonds. At pressure exceeded 45 GPa shear deformation leads to diamond-like carbon (DLC) formation. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3501

Structure of TiAlN Reactive Sputtered Coatings

The Raman spectra, X-ray diffraction and hardness of the TiAlN films co-deposited on the steel substrates by reactive sputtering from Ti and Al targets in a mixture of N2 + Ar gas with two magnetrons at room temperature have been studied. From Raman spectra it is found that the position of high-frequency bands in vibrational spectra was located at 700-730 cm 1 or in the region of 830 850 cm 1 depending on the deposition parameters whereas it is not exceed 630 cm 1 from TiAlN of NaCl structure. It is found the two-phase structure of coatings: a small quantity of NaCl-type structure of TiAlN (TiN) and the disordered structure of the chains of polyhedra [TiNx] with x = 5 and x = 4. The chains of polyhedra [TiNx] with x = 4 are mainly formed at large discharge power of Al(Ti) target or at small content of N2 gas. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2492

Local Ferromagnetism in Microporous Carbon with the Structural Regularity of Zeolite Y

Magnetization M(H,T) measurements have been performed on microporous carbon (MC) with a three-dimensional nano-array structure corresponding to that of a zeolite Y supercage. The obtained results unambiguously demonstrate the occurrence of high-temperature ferromagnetism in MC, probably originating from a topological disorder associated with curved graphene sheets. The results provide evidence that the ferromagnetic behavior of MC is governed by isolated clusters in a broad temperature range, and suggest the occurrence of percolative-type transition with the temperature lowering. A comparative analysis of the results obtained on MC and related materials is given.Comment: To be published in Physical Review B (2003

Far-infrared vibrational properties of high-pressure-high-temperature C60 polymers and the C60 dimer

We report high-resolution far-infrared transmission measurements of the 2 + 2 cycloaddition C-60 dimer and two-dimensional rhombohedral and one-dimensional orthorhombic high-pressure high-temperature C60 polymers. In the spectral region investigated(20-650 cm(-1)), we see no low-energy interball modes, but symmetry breaking of the linked C-60 balls is evident in the complex spectrum of intramolecular modes. Experimental features suggest large splittings or frequency shifts of some IhC60-derived modes that are activated by symmetry reduction, implying that the balls are strongly distorted in these structures. We have calculated the vibrations of all three systems by first-principles quantum molecular dynamics and use them to assign the predominant IhC60 symmetries of observed modes. Pur calculations show unprecedentedly large downshifts of T-1u(2)-derived modes and extremely large splittings of other modes, both of which are consistent with the experimental spectra. For the rhombohedral and orthorhombic polymers, the T-1u(2)-derived mode that is polarized along the bonding direction is calculated to downshift below any T-1u(1)-derived modes. We also identify a previously unassigned feature near 610 cm(-1) in all three systems as a widely split or shifted mode derived from various silent IhC60 vibrations, confirming a strong perturbation model for these linked fullerene structures

Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)

The basic known and hypothetic one- and two-element phases of the B-C-N-O system (both superhard phases having diamond and boron structures and precursors to synthesize them) are described. The attention has been given to the structure, basic mechanical properties, and methods to identify and characterize the materials. For some phases that have been recently described in the literature the synthesis conditions at high pressures and temperatures are indicated.Comment: Review on superhard B-C-N-O phase

TEM study of boron phosphide: Discovery of rhombohedral BP

International audienceMicrostructure of sphalerite (3C) boron phosphide, BP, produced by self-propagated high-temperature synthesis has been studied by high-resolution transmission electron microscopy. Along with numerous twins on the {111}3C plane, layers of wurtzite (2H) polymorphic modification and previously unknown for BP rhombohedral (9R) structure were found which indicates trimorphism of BP

Study on gaseous impurities in alpha-alumina, used single crystals growing

The optimal condition of water content determination in α-AI₂О₃, including sample mixing with methanol followed by titration of the suspension with K.Fisher reagent in the presence of methylene-blue background dye have been found. We have proved the absence of any significant systematic errors by variation of weighed. The determination limit, corresponding to standard deviation of single result 0.3, of the methodic developed is 9•10⁻² mass %. Thermogravimetric and mass-spectrometric data show that α-AI₂О₃ contains not only water, but also significant amounts of СО and СО₂, which, apparently, is the main reason of blowhole-like defects in those single crystals. We assume that material degassing by heating it in vacuum can allow a more effective elimination of such defects in the crystals, than the widely used thermal treatment of the material at atmospheric pressure.Установлены оптимальные условия определения содержания воды в α-AI₂О₃, включающие перемешивание образца с метанолом и последующее титрование полученной суспензии реактивом К.Фишера в присутствии фонового красителя - метиленовой синей. Отсутствие значимых систематических погрешностей доказано при помощи метода варьирования навесок. Предел определения разработанной методики, соответствующий относительному стандартному отклонение единичного результата 0,3, оказался равным 9•10⁻² мас.%. По данным термогравиметрии и масс-спектрометрии установлено, что, кроме воды, α-AI₂О₃ содержит значительные количества СО и СО₂, что, по-видимому, является основной причиной появления в этих монокристаллах дефектов в виде газовых пузырей. Высказано предположение, что дегазация сырья путем его нагревания в вакууме позволит полнее устранять образование в кристаллах указанных дефектов, чем часто применяемая термообработка сырья при атмосферном давленииУстановлено оптимальнi умови визначення вмiсту води в α-AI₂О₃, зокрема, перемiшування зразка з метанолом iз подальшим титруванням одержаної суспензiї реактивом К.Фiшера у присутностi фонового барвника - метиленової синьої. Вiдсутнiсть значущих систематичних похибок доведено за допомогою методу варiювання наважок. Межа визначення розробленої методики, що вiдповiдає, вiдносному стандартному вiдхиленню одиничного результату 0,3, дорiвнює, 9•10⁻² мас.%. За даними термогравiметрiї та мас-спектрометрiї встановлено, що, крiм води, α-AI₂О₃ мiстить значнi кiлькостi СО i СО₂, що, очевидно, є, причиною появи в цих монокристалах дефектiв у виглядi газових бульбашок. Висловлено припущення, що дегазацiя сировини нагрiванням у вакуумi дозволить бiльш ефективно запобiгати утворенню в кристалах вказаних дефектiв, нiж термообробка сировини за атмосферного тиску, яку часто використовують