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1.
Combined theoretical and experimental investigations led to the discovery of a new polymorph of titanium dioxide with titanium nine-coordinated to oxygen in the cotunnite (PbCl 2 ) structure. Hardness measurements on the cotunnite-structured TiO 2 synthesized at pressures above 60 GPa and temperatures above 1000 K reveal that this material is the hardest oxide yet discovered. Furthermore, it is one of the least compressible (with a measured bulk modulus of 431 GPa) and hardest (with a microhardness of 38 GPa) polycrystalline materials studied thus far. 相似文献
2.
S. V. Razorenov A. V. Utkin G. I. Kanel V. E. Fortov A. S. Yarunichev K. Baumung 《高压研究》2013,33(6):367-376
Abstract Measurements of free surface velocity profiles of high-purity titanium samples under shock-wave loading were performed to study the dynamic strength and phase transition parameters. The peak pressure of the initial compression waves was within the range of 4 to 40 GPa, and the load duration was vaned between 10?8 and 10?6 s. An anomalous structure of shock waves was observed at pressures of ~ 2.0 to 5.0 GPa due to the α-ω phase transition. The dynamic strength of pure titanium is lower than that of titanium alloys but exceeds the spall strength of commercial grade titanium. 相似文献
3.
Pressure-induced phase transition of anatase titanium dioxide was investigated by Raman, absorption spectroscopy and X-ray diffraction. The change in Raman and absorption spectra with pressure revealed that the transition from anatase to high pressure phase with f -PbO 2 structure (TiO 2 -II) occurred in the pressure range of 4.0-4.6 GPa for a single crystal. The X-ray powder diffraction patterns indicate the presence of superstructural lattice of anatase at pressures more than 3 GPa. The superstructure of anatase disappears on the release of the pressure. A sluggish transition to the high pressure phase is also observed. The anatase coexists with the high pressure phase at 5.2 GPa. The difference in the results between optical spectroscopy (single crystal) and X-ray diffraction (powder) will be due to crystalinity of the sample. 相似文献
4.
ABSTRACTIn this paper, synthesis of titanium silicon carbide (Ti3SiC2) under high pressure and high-temperature condition has been investigated by using the reactant systems Ti/Si/C, Ti/SiC/TiC, Ti/SiC/C and Ti/TiC/Si. Results reveal that Ti/TiC/Si is unsuited to the synthesis of Ti3SiC2 under a high pressure of 2.0?GPa, while an elemental mixture of Ti/Si/C is applicable. By the addition of Al, Ti3SiC2 with 95.8?wt% purity was obtained from elemental mixture with a large excess of silicon. The optimum experimental parameters were determined as Ti/Si/Al/C having the molar ratio of 3:1.5:0.5:1.9, holding at 2.0?GPa and 1300?°C for 60?min. 相似文献
5.
Abstract The behaviour of bromobenzene (BBe) compressed in a diamond anvill cell up to 30 GPa was studied by XANES and Raman spectroscopy. The liquid-solid transition and a solid-solid transition were observed at 0.9 GPa and 9 GPa respectively. Above 24 GPa, an irreversible transformation occurs to a solid orange-yellow compound which can be recovered at zero pressure. The polymerization mechanism, in connection with the occurence of Br-bonded Sp2 and Sp3 carbons in the solid compound, is discussed. 相似文献
6.
Abstract Energy-dispersive x-ray diffraction using synchrotron radiation was carried out on α-cristobalite to 3 GPa and 350°C in a cubic anvil press. A cascading structural phase transition occurred beyond 0.61 GPa at room temperature. The transition was accompanied by a splitting of most of the a-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increasing temperature. 相似文献
7.
Abstract The crystal structure of ThS2, ThSe2 and US2 has been investigated for pressure up to 60GPa using x-ray powder diffraction. The bulk moduli are 175(10), 155(10) and 155(20) GPa, respectively. A pressure-induced phase transformation occurs at about 40 GPa for ThS2, 30 GPa for ThSe2 and 15 GPa for US2. The results for ThSe2 indicate that its high-pressure phase has a monoclinic structure. The same structure is compatible with the observed high-pressure spectra of ThS2 and US2. However, the crystal system assignment is less certain for these compounds. 相似文献
8.
Abstract The velocity of longitudinal ultrasonic waves, ν1,(P), in polycrystalline cesium was measured at 293 ±1K in the pressure interval 0–5 GPa. v 1(P) alterations at BCC-FCC phase transition at 2.3 GPa and at the electronic-structure transformation at 4.3 GPa were obtained. Decrease of v 1(P) to 4.3 GPa after a maximum at ~3.8 GPa were found, that gave evidence to the appearance of a corresponding soft mode in the FCC-Cs phonon spectrum. The peculiarities of dependence v 1(P) correlate with s-conduction electrons promotion to the empty d-band in accordance with the theoretically predicted continuous electronic s-d transformation in Cs. 相似文献
9.
Abstract High pressure electrical measurements were conducted in the antiferromagnetic insulator CoI, using a miniature Diamond Anvil Cell (DAC). The existence of a Mott Transition predicted from high pressure 129I Mgssbauer Spectroscopy (MS)1 has been verified. At about 8 GPa the system becomes metal1ic as evidenced by the temperature behavior of the conductivity. The conductivity at room temperature, however, still increases with increasing pressure, leveling off at 11 GPa. The metallic behavior in the 8 -11 GPa is explained by coexistence of metallic and insulating clusters via a percolating process. Above 11 GPa the material is completely metallic. This mechanism is consistent with the MS findings. 相似文献
10.
J. L. GarcÍA-MUÑOZ M. Amboage M. Hanfland J. A. Alonso M. J. MartÍNEZ-LOPE R. Mortimer 《高压研究》2013,33(1-2):171-175
The stability under pressure of the charge-density-wave in the insulating phase of YNiO3 was studied by infrared spectroscopy and synchrotron diffraction techniques up to 23 GPa. YNiO3 undergoes a pressure induced insulator-to-metal transition at approximately 15 GPa in the pressure domain, coinciding with the melting of the charge ordered phase. The optical band gap is non-zero above 15 GPa, as is the case above the reported insulator-metal transition (585 K) in the temperature-domain. There is a similarity between the infrared spectral profile around 15 GPa and the infrared spectral profile above ca. 700 K. We conclude therefore that the pressure-induced structural/electronic transition induced around 15 GPa, probably having an as-yet unreported counterpart in the temperature domain at a temperature in excess of 585 K. 相似文献
11.
ABSTRACTThe effects of pressure and temperature on the lattice constants and thermal expansion coefficients of Indium were studied up to 18.6?GPa and 506?K based on in situ X-ray diffraction method with an externally heated diamond anvil cell. The results show that the measured axial ratio (c/a) decreases with increasing temperature and its temperature dependence decreases with increasing pressure. The thermal expansion coefficient of the a-axis decreases with increasing pressure up to 7?GPa and remains almost constant above 7?GPa, whereas that of the c-axis increases monotonously with pressure and changes from negative to positive at around 7?GPa. The observed behavior suggests that temperature reduces the tetragonal distortion on the lattice, and its effect is dominant below 7?GPa; in contrast, pressure enhances lattice distortion, and tends to have a stronger effect above 7?GPa. 相似文献
12.
Abstract Review of phase transitions and equations of state at multimegabar pressures (100–300 GPa) is presented. Energy dispersive x-ray diffraction techniques in conjunction with synchrotron radiation sources are used. Besides several transition metals, Pt to 282 GPa, Re to 251 GPa, W to 209 GPa, and Fe to 255 GPa, the special focus is on Group IVA elements and isoelectronic III-V compounds. At high pressure, the isoelectronic materials are isostructural and exhibit similar equation of state. 相似文献
13.
Abstract Raman spectra of PbMoO4 have been measured up to 31 GPa in a diamond anvil cell (DAC). Two new phases were found at 10 and 16 GPa pressures at room temperature. 相似文献
14.
J. Badro J.P. Itié A. Polian 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):265-268
X-ray diffraction (XRD) experiments have been carried out on quartz-like GaPO4 at high pressure and room temperature. A transition to a high pressure disordered crystalline form occurs at 13.5 GPa. Slight
heating using a YAG infrared laser was applied at 17 GPa in order to crystallize the phase in its stability field. The structure
of this phase is orthorhombic with space group Cmcm. The cell parameters at the pressure of transition are a
=7.306?, b
=5.887? and c
=5.124?.
Received: 7 October 1997 / Received in final form: 17 November 1997 / Accepted: 18 November 1997 相似文献
15.
Abstract Stabilities of SiO2 stishovite and CaSiO3 perovskite were studied up to 120 GPa, using diamond-anvil type high pressure apparatus combined with a laser heating system. High pressure in situ X-ray observation clarified that stishovite distorts into slightly dense CaCl2-type structure above 80 GPa while cubic perovskite type CaSiO3 remains stable up to 120 GPa. 相似文献
16.
Abstract The temperature and enthalpy of melting for poly(ethy1ene oxide) have, for the first time, been studied as a fuction of pressure up to 1 GPa by means of differential scanning calorimetry. The initial increase of the temperature of melting with increasing pressure is 64 K/GPa, whereas the enthalpy decreases by 40% in the 1 GPa pressure range. Using Clausius-Clapeyrons equation the volume change on melting is estimated to be 1.5 cm3/mol. The glass transition temperature Tg for polystyrene has also been studied by the same technique for pressures up to 0.1 GPa. The measurements show that Tg increases with increasing pressure by 250 K/GPa. 相似文献
17.
Abstract Plutonium monoselenide was studied under high pressure up to 47 GPa, at room temperature, using a diamond anvil cell in an energy dispersive X-ray diffraction facility. At ambient pressure, PuSe has the NaC1-type (B1) structure. The compound has been found to undergo a second-order crystallographic phase transition at around 20 GPa. This phase can be described as a distorted B1 structure, with a rhombohedral symmetry. PuSe transforms to a new phase at around 35 GPa, which can be indexed in the cubic CsCl-type (B2). The volume collapse at this phase transition is 11%. When releasing pressure, we observed a strong hysteresis to the inverse transformation down to 5 GPa. From the pressure-volume relationship, the bulk modulus has been determined to B 0 = 98 GPa and its pressure derivative as B 0 = 2.6. These results are compared to those obtained with other actinide monmictides and monochalcogenides. 相似文献
18.
Abstract Two monoclinic pyroxenes of composition Ca(Fe,Mg)Si2O6 were studied up to 10 GPa using X-ray powder diffraction and 57Fe Mössbauerspectroscopy. The results are indicative of a phase transition at 4 GPa. 相似文献
19.
Abstract The structural behaviour of Pm metal has been investigated up to 60 GPa of pressure using a Diamond Anvil Cell (DAC) and the energy dispersive X-ray diffraction technique. The room temperature/pressure structural form of Pm is dhcp and it transforms to a fcc phase by 10 GPa. This cubic phase of the metal converts by 18 GPa to a third phase, which has frequently been referred to as representing a distorted fcc structure. This latter form of Pm was retained up to 60 GPa, the maximum pressure studied, but subtle changes in the X-ray spectra between 50 and 60 GPa hinted that an additional structural change could be forthcoming at higher pressures. From the experimental data a bulk modulus (B0) of 38 GPa and a B0′ constant of 1.5 were calculated using the Birch equation. This modulus for Pm is in accord with the moduli reported for the neighboring lanthanide metals. 相似文献
20.
E. V. Shorokhov I. N. Zhgilev D. V. Gunderov A. A. Gurov 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(2):251-254
Dynamic equal-channel angular pressing, a new method for the intense plastic deformation of materials, was developed and applied to titanium, as an example. A sample, accelerated in a gun to a velocity of 300 m/s, impinged on a matrix with intesecting channels. The deformation of titanium occurred at a shear-deformation rate of 104–105 s?1 and pressure of several GPa. Upon deformation, the strength of titanium increased by a factor of 2, with the plasticity remaining at an acceptable level. Metallographic and electron microscopy analyses demonstrated that, under the action of intense deformation, the initial course-grained structure of titanium transforms into an ultrafine-grained one. 相似文献