| 1. |
- Abrikosov, Igor, et al.
(författare)
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Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
- 2015
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Ingår i: High Pressure Research. - : Taylor andamp; Francis: STM, Behavioural Science and Public Health Titles. - 0895-7959 .- 1477-2299. ; 35:1, s. 42-48
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Tidskriftsartikel (refereegranskat)abstract
- We discuss theoretical description of pressure-induced phase transitions by means of first-principles calculations in the framework of density functional theory. We illustrate applications of theoretical tools that allow one to take into account configurational and vibrational disorders, considering Ti-V alloys as a model system. The universality of the first-principles theory allows us to apply it in studies of different phenomena that occur in the Ti-V system upon compression. Besides the transitions between different crystal structures, we discuss isostructural transitions in bcc Ti-V alloys. Moreover, we present arguments for possible electronic transitions in this system, which may explain peculiar behaviour of elastic properties of V upon compression.
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| 2. |
- Ahuja, Rajeev, et al.
(författare)
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High-pressure structural transitions in Cm and Am0.5Cm0.5 binary alloy
- 2006
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26:4, s. 377-381
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Tidskriftsartikel (refereegranskat)abstract
- The high-pressure behaviour of Cm and Am0.5Cm0.5 binary alloy is investigated theoretically using ab initio electronic structure methods. Our calculations reproduce the structural phase transitions, which are observed in recent experiment performed by Heathman et al. [S. Heathman, R.G. Haire, I Le Bihan et al., Science 309 110 (2005)] and Lindbaum et al. [A. Lindbaum, S. Heathman, T. Le Bihan et al., J. Phys: Condens. Matter 15 S2297 (2003)]. Calculated transition pressures are in reasonable agreement with the experimental values. Calculations performed for an antiferromagnetic state are essential to reproduce the stability of Cm-III phase.
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| 3. |
- Andersson, Britt M., et al.
(författare)
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Electrical resistivity and critical temperature of Bi-based high-Tc superconductors to 1 GPa
- 1990
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Ingår i: High Pressure Research, volumes 3 to 5. - London : Gordon and Breach. - 2881247466 ; 3:1-6, s. 120-122
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Konferensbidrag (refereegranskat)abstract
- We have measured the electrical resistance R of a sintered, two-phase, high-TC superconductor with the nominal composition BiSrCaCu2Ox, as a function of T and p. We find d(lnR)/dp ≃ -0.06 GPa-1 at 295 K, while dTC/dp is 2.5 K/GPa for the phase with Tc ≃ 76 and 2 K/GPa for that with TC ≃ 106 K.
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| 4. |
- Andersson, Britt M., et al.
(författare)
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High-pressure properties of high-Tc superconductor samples produced by hot isostatic pressing
- 1990
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Ingår i: High Pressure Research, volumes 3 to 5. - London : Gordon and Breach. - 2881247466 ; 3:1-6, s. 123-125
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Konferensbidrag (refereegranskat)abstract
- The electrical resistance of dense YBa2Cu3Ox and YBa2Cu4Oy produced by hot isostatic pressing has been measured vs. T and p. At 295 K we find d (ln R)/dp ≃ -0.12 and -0.09 GPa-1, respectively, with no systematic dependence on initial density. For 1-2-4, dTC/dp ≃ 5.1 K/GPa, which is ten times that of 1-2-3.
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| 5. |
- Andersson, Ove, et al.
(författare)
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A low-temperature high-pressure apparatus with a temperature control system
- 1992
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 10:4, s. 599-606
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Tidskriftsartikel (refereegranskat)abstract
- A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm3. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.
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| 6. |
- Andrault, D, et al.
(författare)
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Study of partial melting at high-pressure using in situ X-ray diffraction
- 2006
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26:3, s. 267-276
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Tidskriftsartikel (refereegranskat)abstract
- The high-pressure melting behavior of different iron alloys was investigated using the classical synchrotron-based in situ X-ray diffraction techniques. As they offer specific advantages and disadvantages, both energy-dispersive (EDX) and angle-dispersive (ADX) X-ray diffraction methods were performed at the BL04B1 beamline of SPring8 (Japan) and at the ID27-30 beamline of the ESRF (France), respectively. High-pressure vessels and pressure ranges investigated include the Paris- Edinburgh press from 2 to 17GPa, the SPEED-1500 multi-anvil press from 10 to 27 GPa, and the laser-heated diamond anvil cell from 15 to 60 GPa. The onset of melting (at the solidus or eutectic temperature) can be easily detected using EDX because the grains start to rotate relative to the X-ray beam, which provokes rapid and drastic changes with time of the peak growth rate. Then, the degree of melting can be determined, using both EDX and ADX, from the intensity of diffuse X-ray scattering characteristic of the liquid phase. This diffuse contribution can be easily differentiated from the Compton diffusion of the pressure medium because they have different shapes in the diffraction patterns. Information about the composition and/or about the structure of the liquid phase can then be extracted from the shape of the diffuse X-ray scattering.
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| 7. |
- Arvanitidis, J., et al.
(författare)
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High pressure study of the 2D polymeric phase of C60 by means of Raman spectroscopy
- 2001
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 18:1-6, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- The effect of high hydrostatic pressure, up to 12GPa, on the intramolecular phonon frequencies and the material stability of the two-dimensional tetragonal Cm polymer has been studied by means of Raman spectroscopy in the spectral range of the radial intramolecular modes (200-800cm-1). A number of new Raman modes appear in the spectrum for pressures ≈ 1.4 and ≈ 5.0 GPa. The pressure coefficients for the majority of the phonon modes exhibit changes to lower values at P=4.0 GPa, which may be related to a structural modification of the 2D polymer to a more isotropic phase. The peculiarities observed in the Raman spectra are reversible and the material is stable in the pressure region investigated.
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| 8. |
- Arvanitidis, J., et al.
(författare)
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High pressure study of the 2D polymeric phase of C60by means of raman spectroscopy
- 2000
-
Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 18:1-6, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- The effect of high hydrostatic pressure, up to 12 GPa, on the intramolecular phonon frequencies and the material stability of the two-dimensional tetragonal C-60 polymer has been studied by means of Raman spectroscopy in the spectral range of the radial intramolecular modes (200-800 cm(-1)). A number of new Raman modes appear in the spectrum for pressures similar to 1.4 and similar to 5.0 GPa. The pressure coefficients for the majority of the phonon modes exhibit changes to lower values at P=4.0 GPa, which may be related to a structural modification of the 2D polymer to a more isotropic phase. The peculiarities observed in the Raman spectra are reversible and the material is stable in the pressure region investigated.
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| 9. |
- Berg, Sven, et al.
(författare)
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High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus
- 2012
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 32:4, s. 490-508
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Tidskriftsartikel (refereegranskat)abstract
- For investigating high pressure sintering processes, numerical models can be used. This will demand material models which give realistic mechanical response throughout the whole parameter space of the actual process. As the pressures become higher, the material density approaches its full theoretical value and the elastic part of the material properties becomes increasingly important. In this investigation, Poisson's ratio was determined using ultrasonic pulse-echo measurements. A new elastic model and an improved plasticity model were implemented into a user-defined material subroutine in a finite element (FE) code. To experimentally investigate the load displacement response and pressure distribution in powder compacts during pressing, a pressure instrumented Bridgman anvil apparatus was used. Validation of the FE model was conducted against experimental data from pressing experiments using two different start densities. The results show that the simulation model is indeed capable of reproducing load–thickness curves and pressure profiles reasonable close to the experimental curves.
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| 10. |
- Dubrovinskaia, N., et al.
(författare)
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Compressibility of boron-doped diamond
- 2006
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26, No. 2, s. 79-85
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Tidskriftsartikel (refereegranskat)
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| 11. |
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| 12. |
- Hsu, Ying-Jui, et al.
(författare)
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Development of a high pressure stirring cell up to 2 GPa : a new window for chemical reactions and material synthesis
- 2020
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 40:3, s. 358-368
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Tidskriftsartikel (refereegranskat)abstract
- A new method for stirring under high pressure conditions has been developed and tested. The key component is a Teflon cell assembly equipped with magnetic stirring function, which is capable to operate across a wide pressure range, up to at least 2 GPa, in a large volume press. The setup enables adjustable stirrer rotation rate and detection of stirring in a sample,e.g.to observe liquid-solid phase transitions at high pressure. The viscosity limit of stirring is ca. 500 times that of water at room temperature (i.e.similar to 500 mPas). Moreover, we show that zinc oxide nanoparticles hydrothermally synthesized at 0.5 GPa and 100 degrees C under stirring conditions show an order of magnitude smaller size (100 nm) compared to those synthesized under non-stirring conditions (1 mu m). The wide pressure range for stirring of viscous media opens interesting possibilities to produce novel materials via hydrothermal synthesis and chemical reactions.
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| 13. |
- Konopkova, Zuzana, et al.
(författare)
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Thermal conductivity of hcp iron at high pressure and temperature
- 2011
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 31:1, s. 228-236
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Tidskriftsartikel (refereegranskat)abstract
- Results of steady-state heat transfer experiments on iron in laser-heated diamond anvil cell, combined with numerical simulation using finite-element method are reported. Thermal boundary conditions, dimensions of sample assemblage, heating-laser beam characteristics and relevant optical properties have been well defined in the course of experiments. The thermal conductivity of the polycrystalline hexagonal-iron foil has been determined up to pressure 70GPa and temperature 2000K. At these conditions, the conductivity value of 32 ± 7W/mK was found. Sources of errors arising from uncertainties in input parameters and applied experimental procedures are discussed. Considering results of earlier preferred-orientation studies in diamond anvil cell, an averaging effect of polycrystalline texture on the intrinsic anisotropy is assumed. The obtained conductivity is interpreted as an effective value, falling in between the upper and lower bounds on the average conductivity of a random aggregate of uniaxial crystals.
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| 14. |
- Leinbach, Logan J., et al.
(författare)
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Large volume multianvil cell assembly for hydrothermal synthesis and conversions up to 6.5 GPa and 400°C
- 2023
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Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 43:3, s. 231-250
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Tidskriftsartikel (refereegranskat)abstract
- A multianvil cell assembly with octahedral edge length 25 mm has been adapted for high pressure investigations involving water-rich environments up to 6.5 GPa and 400°C. Water-rich samples are confined in Teflon containers with a volume up to 300 mm3. Applicability tests were performed between 250 and 400°C by investigating the transformation of amorphous titania particles close to the rutile–TiO2-II (∼5 GPa) phase boundary, and the transformation of amorphous silica particles close to the quartz–coesite (∼2.5 GPa) and coesite–stishovite (∼7 GPa) phase boundaries. The performed experiments employed 25.4 mm tungsten carbide anvils with a truncation edge length of 15 mm. The sample pressure at loads approaching 820 t was estimated to be around 6.5 GPa. The large volume multianvil cell is expected to have broad and varied application areas, ranging from the simulation of geofluids to hydrothermal synthesis and conversion/crystal growth in aqueous environments at gigapascal pressures.
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| 15. |
- Leonov, I., et al.
(författare)
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Mott transition and magnetic collapse in iron-bearing compounds under high pressure
- 2017
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Ingår i: High Pressure Research. - : TAYLOR & FRANCIS LTD. - 0895-7959 .- 1477-2299. ; 37:2, s. 96-118
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the electronic, magnetic, and related structural transitions in the iron-based Mott insulators under high pressures relevant to the Earths lower mantle conditions. The paper focuses on the above-mentioned topics based primarily on our theoretical analysis and various experimental studies employing synchrotron X-ray diffraction, Fe-57 Mossbauer spectroscopy, and electrical transport measurements. We review the main theoretical tools employed for the analysis of the properties of materials with strongly interacting electrons and discuss the problems of theoretical description of such systems. In particular, we discuss a state-of-the-art method for calculating the electronic structure of strongly correlated materials, the DFT + DMFT method, which merges standard band-structure techniques (DFT) with dynamical mean-field theory of correlated electrons (DMFT). We employ this method to study the pressure-induced magnetic collapse in Mott insulators, such as wustite (FeO), magnesiowustite (Fe1-xMgx)O (x=0.25 and 0.75) and goethite (FeOOH), and explore the consequences of the magnetic collapse for the electronic structure and phase stability of these materials. We show that the paramagnetic cubic B1-structured FeO and (Fe,Mg)O and distorted orthorhombic (Pnma) FeOOH exhibit upon compression a high-to low-spin (HS-LS) transition, which is accompanied by a simultaneous collapse of local moments. However, the HS-LS transition is found to have different consequences for the electronic properties of these compounds. For FeO and (Fe0.75Mg0.25)O, the transition is found to be accompanied by a Mott insulator-to-metal phase transition. In contrast to that, both (Fe0.25Mg0.75)O and FeOOH remain insulating up to the highest studied pressures, indicating that a Mott insulator to band insulator phase transition takes place. Our combined theoretical and experimental studies indicate a crossover between localized to itinerant moment behavior to accompany magnetic collapse of Fe ions.
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| 16. |
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| 17. |
- Li, S., et al.
(författare)
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Crystallographic structures of PbWO4
- 2003
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 23:3, s. 343-347
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Tidskriftsartikel (refereegranskat)
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| 18. |
- Liu, Lei, et al.
(författare)
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Lattice distortion-induced sluggish phasetransition in CoCrFeNixAl1-x (x = 0.5, 0.75) highentropyalloys at high pressures
- 2019
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 39:4
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys (HEAs) attract growing interest due to their remarkable properties. However, our knowledge of the mechanism of phase stability of HEAs is still very limited. Herein, CoCrFeNixAl1-x (x = 0.5 and 0.75) were compressed to high pressures to investigate the lattice distortion effect on their phase stability. It was discovered that both bcc CoCrFeNi0.5Al0.5 and fcc CoCrFeNi0.75Al0.25 alloys transform to the hcp structure at high pressures, following a gradual phase transition. The sluggish character of these transitions perhaps originates from the local energy fluctuations caused by the chemical disorder. The phase transitions in both studied compounds commenced when their intrinsic lattice strain had reached the maximum value, indicating that the lattice distortion effect plays a key role in these crystallographic structure-transforming processes. These results provide fundamental information on the phase selection rules of HEAs, which are important for physical metallurgy theories and HEAs design in the future.
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| 19. |
- Mattesini, M, et al.
(författare)
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An ab initio study of S-substituted iron-nickel-silicon alloy at the Earth's inner core pressure
- 2008
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 28:4, s. 437-441
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic stability of S-substituting Si into a bcc Fe0.80Ni0.05SxSi(0.15-x) random alloy, with x=0.025 n (n=0-- 4), was investigated up to 350GPa by using an ab initio density functional method based on the full charge density-exact muffin-tin orbital-coherent potential approximation scheme. From the analysis of the calculated H values, we suggest that the FeNiSSi stoichiometry with zero sulphur content always behaves as the most stable system along the whole pressure range of 0-350GPa. As a general tendency, we found that the alloys with 6.8-8.1wt.% Si are energetically more stable than those with lower silicon content, thus supporting the dissolution mechanism for the Earth's inner core compositional model.
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| 20. |
- Moser, D., et al.
(författare)
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An in situ neutron diffraction measurement of the pressure-temperature evolution of a MgD2:TiD2 mixture
- 2010
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 30:4, s. 643-652
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen storage capacity of Mg-Ti-H films is approximately five times that of conventional metal hydride electrodes in NiMH-batteries. Mg and Ti are considered to be immiscible in the bulk and the ambient pressure phase diagram of Mg and Ti indicates that no binary stable bulk compounds are formed. However, in the presence of hydrogen, an Mg-Ti-H phase has been obtained by Kyoi et al. using a high pressure synthesis - where magnesium hydride is compacted with different TM-hydrides in an anvil cell at pressures of the order several GPa (4-8GPa) and at a temperature of 873K. In this work, we have proved the feasibility of in situ powder diffraction using the Paris-Edinburgh high pressure cell for the observation of structural changes on this system and we propose modifications to improve the output of the experiment.
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| 21. |
- Ohlin, C André, et al.
(författare)
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Carbon dioxide reduction in biphasic aqueous-ionic liquid systems by pressurized hydrogen
- 2003
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 23:3, s. 239-242
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Tidskriftsartikel (refereegranskat)abstract
- This work reports the hydrogenation of carbon dioxide/inorganic carbonate salts to formic acid/formate in two phase systems comprising an ionic phase, in which the catalyst is immobilized, and an aqueous phase in which the carbonates and formate are confined, is reported. The reactions were followed in situ by multinuclear NMR. Pressurized H-2 gas was used for the reduction.
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| 22. |
- Olsen, J. Staun, et al.
(författare)
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High-pressure structural behavior of the double perovskite Sr2CrReO6 : an experimental and theoretical study
- 2009
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 29:1, s. 83-86
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Tidskriftsartikel (refereegranskat)abstract
- The high-pressure structural behavior of Sr2CrReO6 has been studied experimentally using synchrotron radiation and the diamond anvil cell and theoretically using density functional theory. The experimental zero-pressure bulk modulus is B0=1704GPa and the pressure derivative is B0'=4.71.0. These results compare well with the calculated values 172.6GPa and 5.7. A pseudo-cubic unit cell can describe the crystal structure at low pressure, but the tetragonal structure becomes evident at high pressure.
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| 23. |
- Spektor, Kristina, et al.
(författare)
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Crystallization of mesoporous silica SBA-15 in a high pressure hydrothermal environment
- 2017
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Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 37:3, s. 345-359
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous silica SBA-15 (with similar to 6 nm pore size and similar to 6 nm wall thickness) was exposed to a hydrothermal environment at 2 and 5GPa. The p,T quenched products were investigated by powder X-ray diffraction and transmission electron microscopy. Infrared spectroscopy and thermogravimetric analysis of a sample subjected to 5GPa at room temperature suggests functionalization of both inner and outer pore surface by silanol. Partial transformation to nano-sized (20-50 nm) coesite crystals with nonfaceted morphology was observed during short equilibration times of 2h at 125 degrees C, which is significantly below the melting point of water (similar to 250 degrees C). Untransformed SBA-15 maintained intact pore structure. At 175 degrees C and during 8h, SBA-15 transformed completely into faceted coesite crystals with dimensions 100-300 nm, suggesting Ostwald ripening and thus significant mass transport in the solid water environment. At 2GPa the melting point of water is near 70 degrees C. Partial transformation to nano-sized alpha-quartz was observed at 65 degrees C and during 2h. Untransformed SBA-15 partially pore collapsed. The reduced pore stability of SBA-15 at 2GPa is attributed to the presence of liquid water in the pores due to melting point depression of confined water.
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| 24. |
- Sundqvist, Bertil, et al.
(författare)
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Ionic conductivity in three crystalline phases of LiBH4 under pressure
- 2013
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Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 33:1, s. 141-151
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Tidskriftsartikel (refereegranskat)abstract
- The AC electrical conductivity of LiBH4 was investigated below 2GPa between 1Hz and 1.6MHz. The high-temperature phase has an ionic conductivity of up to 0.01Scm(1), while the low-temperature phases have conductivities two orders of magnitude lower. All phases show an Arrhenius behaviour with activation energies E-a between 0.5 and 0.7eV, in good agreement with earlier data except for phase III, which is found to have the highest activation energy of the phases studied. The high-temperature phase has a minimum in E-a near 1GPa, close to the triple point, correlated with a sudden change in activation volume. These features may indicate an isostructural phase transition. The conductivities of the ambient temperature phases increase temporarily by an order of magnitude after transitions between these phases, probably due to new diffusion channels via structural defects. The phase diagram agrees well with earlier results.
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| 25. |
- Talyzin, Alexandr, et al.
(författare)
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High pressure study of NaAlH4 by Raman spectroscopy up to 17 GPa
- 2006
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26:3, s. 165-73
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Tidskriftsartikel (refereegranskat)abstract
- A high-pressure Raman study was carried out on NaA1H(4) up to 17 GPa using the diamond anvil cell method. In the pressure region 2-5 GPa, several of the original modes split. Although this might be a sign of some structural change, the spectral changes do not allow us to claim the existence of a clear phase transition in this pressure range. The spectra revert to their ambient pressure forms on decreasing pressure below < 3.0-1.4 GPa. A phase transition to beta-NaA1H(4) was found at 14-16 GPa. This phase transition is also reversible with an unusually strong hysteresis: the beta-NaA1H(4) can be followed upon decompression down to 3.9 GPa. Analysis of Raman data shows that this phase transition is compatible with a theoretical prediction of a strong volume collapse.
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| 26. |
- Tonpheng, Bounphanh, et al.
(författare)
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In situ high-pressure vulcanization and thermal properties of polyisoprene
- 2006
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Ingår i: High Pressure Research vol. 26. - : Taylor & Francis. ; , s. 415-419
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Konferensbidrag (refereegranskat)abstract
- Liquid cis-1,4-poly(isoprene) (PI) has been vulcanized under high pressures without using additives. Moreover, the thermal conductivity and heat capacity per unit volume of both unvulcanized (liquid state at room temperature) and vulcanized (rubbery state) PI have been measured, and found to be the same in both states. However, the relaxation behavior associated with the glass transition differs. The unvulcanized PI exhibits two clearly resolved relaxation processes near the glass transition whereas these tend to combine into one process in the vulcanized PI. Moreover, at the same pressure temperature co-ordinate, the relaxation time of the vulcanized sample (1 s at 220 K at atmospheric pressure) is longer than that of the unvulcanized sample.
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| 27. |
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| 28. |
- Wunschel, M, et al.
(författare)
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High-pressure phase transitions in tetrakis(trimethylsilyl)silane Si[Si(CH3)(3)](4)
- 2003
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Ingår i: High Pressure Research. - : Informa UK Limited. - 1477-2299 .- 0895-7959. ; 23:4, s. 425-437
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Tidskriftsartikel (refereegranskat)abstract
- The compound tetrakis(trimethylsilyl)silane S-i[Si(CH3,)(3)](4) (TSi) has been studied at room temperature for pressures up to 2 1.5(1) GPa, using X-ray powder diffraction with synchrotron radiation. Three different phases are reported in the investigated pressure range. The c.c.p.-type structure is stable up to a pressure of 0.19(1) GPa (Fm (3) over barm, a = 13.52110)Angstrom, V = 2471.95(1)Angstrom(3), Z = 4 at 0.02(1)GPa). It shows a severe orientational disorder of the molecules. At pressures 0.19(1)-0.71(1)GPa a monoclinic phase (HP1) is found with space group P2(1)/n and Z=8 (a = 17.746(1)Angstrom, b = 16.098(1)Angstrom, c= 16.871(1)Angstrom, gamma = 111.437(5)degrees and V = 4486.3(8) Angstrom(3) at 0.24(1)GPa). Another monoclinic phase (HP2) exists at pressures 0.52(1)-8.67(5)GPa. This phase has a smaller unit cell than the HP1 phase with Z(.)=2 (a =8.3778(8)Angstrom, b=9.1050(7)Angstrom, c= 13.3024(8)Angstrom, gamma= 111.63(1)degrees and V = 943.22(6) Angstrom(3) at 1.73(2)GPa). The pressure dependencies of the unit-cell volumes are successfully described by Mumaghan or Vinet-type equations of state. The structures at different pressures and temperatures of TSi and related compounds are described as distorted superstructures of the c.c.p. arrangement. The occurrence of different superstructures is rationalized as the result of an optimized packing of ordered molecules of various shapes.
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| 29. |
- Wågberg, Thomas, et al.
(författare)
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2D polymerization and doping of fullerenes under pressure
- 2000
-
Ingår i: High Pressure Research vol. 18. - : Gordon & Breach. ; 18:1-6, s. 139-143
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Konferensbidrag (refereegranskat)abstract
- Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.
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| 30. |
- You, Shujie, et al.
(författare)
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Probing structural stability of double-walled carbon nanotubes at high non-hydrostatic pressure by Raman spectroscopy
- 2011
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 31:1, s. 186-190
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations predict that the collapse pressure for double-walled carbon nanotubes (DWCNTs) is proportional to 1/R3, where R is the effective or average radius of a DWCNT. In order to address the problem of CNT stability at high pressure and stress, we performed a resonance Raman study of DWCNTs dispersed in sodium cholate using 532 and 633 nm laser excitation. Raman spectra of the recovered samples show minor versus irreversible changes with increasing ID/IG ratio after exposure to high non-hydrostatic pressure of 23 and 35 GPa, respectively. The system exhibits nearly 70% pressure hysteresis in radial breathing vibrational mode signals recovery on pressure release which is twice that predicted by theory.
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| 31. |
- Ahuja, R
(författare)
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High pressure studies of sodium and silver halides
- 2000
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Ingår i: HIGH PRESSURE RESEARCH. - : GORDON BREACH SCI PUBL LTD. - 0895-7959. ; 18:1-6, s. 131-138
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the structural phase transitions in sodium and silver halides theoretically under high compressions by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential
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