Papers by Keyword: High-Pressure

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Authors: M.V. Magnitskaya, E.T. Kulatov, A.A. Titov, Y.A. Uspenskii, E.G. Maksimov, S.V. Popova, V.V. Brazhkin
Abstract: We report on ab initio density-functional calculations of a novel spintronics-related compound CrGa2Sb2 recently synthesized under high pressure. The effect of Cr deficiency on the electronic, magnetic and optical properties of CrGa2Sb2 is considered. New X-ray structural measurements up to high pressure of 9 GPa are presented.
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Authors: Yeshvir Singh Panwar, Mahendra Aynyas, Jagdeesh Pataiya, Sankar P. Sanyal
Abstract: The electronic structure and high pressure structural phase transition of SmTe and SmPo have been studied by using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). The total energy as a function of volume is obtained and it is found that these compounds are stable in NaCl-type (B1-phase) structure and transform to CsCl-type (B2-type) structure. The transition pressure of SmTe and SmPo are found to be 6.6 GPa and 8.6 GPa respectively. We have also calculated lattice parameter (a0), bulk modulus (B0), band structure (BS) and density of states (DOS). From energy band diagram, we observed that these compounds exhibit weakly metallic behaviour. The calculated values of lattice parameter and bulk modulus agree well with the available data.
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Authors: A.I. Harkunov, V.E. Antonov, O.I. Barkalov, M. Calvo-Dahlborg, U. Dahlborg, V.K. Fedotov, E.G. Ponyatovsky, M. Winzenick
241
Authors: Ming Horng Su, Hung Chang Chen
Abstract: This paper studies the phase transitions of Cu and Ni alloys as they cool from melting temperature to room temperature under high-pressure conditions. The interatomic forces acting between the atoms are modeled by the tight-binding potential. Control over the environmental pressure and the cooling temperature is maintained by a canonical ensemble (N, P, T) system. The numerical results confirm that the metal phase transition is influenced significantly by the pressure conditions, even in the case of pure Cu and Ni metals. Three specific transition pathways are identified for the Cu and Ni alloys as they cool from melting temperature to room temperature, namely a transition at the melting temperature to a crystalline structure, a transition at the glass transition temperature to a glass (amorphous) structure, and finally solidification at the melting temperature followed by a subsequent transition at the glass transition temperature. The results reveal that glass transition generally occurs at lower pressures in alloys with higher Cu compositions, while glass transition following prior solidification tends to takes place at higher pressures in alloys with higher Ni compositions.
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Authors: Keiki Yamamoto, Noboru Yuasa, Isamu Matsui, Toshihiko Hiaki, Satoshi Tanaka
Abstract: Supercritical water (SCW) has both the solvent power approximate to liquids and the transport properties common to gases. It is therefore expected as an excellent solvent for industrial waste treatment. In this study, various building materials were treated with SCW, and their morphological changes after treatment were observed. The effects of SCW treatment on the pore structure and compressive strength of cement concrete and mortar were also investigated. In the range of this study, after SCW treatment, inorganic materials and organic materials can be recovered as solids and liquids, respectively. Under sub-critical and super-critical temperature and pressure conditions, compressive strength of mortar decreases, while the effective pore volume increases.
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Authors: Veneta Grigorova, Dimitar Roussev
Abstract: In the present study we elaborated a thermodynamical model for analysis of isothermal phase transformations under high pressure. Our study was provoked by the necessity to characterise the behaviour of MTe2 chemical compounds (M = Pd, Pt) while subjected isothermally to high pressure. As known [1] MTe2 powders are representatives of the CdI2 structure type. This structure type is a bi-dimensional one and as such is atypical for the big family of lamellar MQ2-type dichalcogenides (M = Pd, Pt; Q = S, Se, Te). Specific of lamellar structure is the strong ionicity of the bonds. One of the most interesting points stands on the possibility for realising interactions between the layers of different types of ions. That could be done under high pressure by any of the following transformation processes: (i) phase transition to the typical pyrite structure; (ii) phase rearrangement changing the parameters of the crystal cell but keeping the 2D-type structure. In this framework our aim was to elaborate a thermodynamical model for analysis of such isothermal phase transformations under high pressure. Our analysis model is designed to answer the following questions: (i) if the treated compound undergoes a classical phase transition or a phase rearrangement; (ii) which is the order of the phase transition or the phase rearrangement, respectively; and (iii) what is the degree-of-stability of the treated compound under high pressure. To detect if the transformation process is a phase transition or a rearrangement, we compute both volumetric and longitudinal Gibbs free energies and their partial derivatives. We recognise the transformation to be: (i) a phase transition when it affects the volumetric Gibbs free energy and its partial derivatives; (ii) a phase rearrangement if it affects the longitudinal Gibbs free energy and its partial derivatives. The order of the transformation process (phase transition or rearrangement, respectively) is determined by the order of the partial derivative of the Gibbs free energy (volumetric or longitudinal, respectively), which is discontinuous in the transformation point. Hence, we compute the two first partial derivatives (i.e., the first one and the second one) of the Gibbs free energy (both volumetric and longitudinal). For characterising the degree of stability of the treated compound under high pressure we calculate its entropy generation (volumetric and longitudinal, respectively) during the treatment process. The established model was further applied to PdTe2 and to PtTe2 while subjected isothermally to high pressure.
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Authors: Andrzej Misiuk, Alexander G. Ulyashin, Adam Barcz, Peter Formanek
Abstract: Accumulation of hydrogen in Czochralski silicon implanted with N2+ (Si:N; N dose, DN=1–1.8x1018 cm-2; energy E=140 keV) or O2+ (Si:O; DO=1x1017 cm-2; E=200 keV), processed at up to 1400 K (HT) under enhanced Ar pressure, up to 1.2 GPa (HP), and followed by treatment in hydrogen (deuterium) plasma, was investigated by Secondary Ion Mass Spectroscopy. Implantation produces buried amorphous layer. As determined by transmission electron microscopy, subsequent HT-HP processing results in a formation of a specific sample microstructure. In plasma treated as-implanted Si:N, hydrogen accumulates at a depth of about 50 nm, up to concentration 2x1021 cm-3. This concentration is twice lower at a depth ≈ 80–250 nm. Deuterium content remains almost unchanged after plasma treatment of Si:N prepared by processing at 1270 K while it is strongly dependent on DN and on HP. In plasma treated Si:O, prepared by processing at 920-1230 K, hydrogen profile corresponds to that of implanted oxygen and decreases with HP. Comparative analysis of hydrogen accumulation and its subsequent release at 720-920 K in the Si:N and Si:O structures indicates that the capacity of buried layers in Si:O to getter and to preserve hydrogen is higher than that in Si:N.
319
Authors: Peter Kroll
Abstract: A combination of first-principle and thermochemical calculations is applied to compute the phase diagrams of rhenium-nitrogen and of ruthenium-nitrogen at elevated temperature and high pressure. We augment total energy calculations with our approach to treat the nitrogen fugacity at high pressures. We predict a sequential nitridation of Re at high-pressure/high-temperature conditions. At 3000 K, ReN will form from Re and nitrogen at about 32 GPa. A ReN2 with CoSb2-type structure may be achieved at pressures exceeding 50 GPa at this temperature. Marcasite-type RuN2 will be attainable at 3000 K at pressures above 30 GPa by reacting Ru with nitrogen.
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Authors: Jian Yu Huang, Yuntian T. Zhu
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