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1.
运用密度泛函理论研究了钒(Vanadium)在高压下的结构相变。 通过对体心立方(bcc)结构的钒在不同压强下剪切弹性系数C44的计算, 发现当压强约95 GPa时 C44<0, 说明体心立方结构的钒在此条件下是不稳定的。 进一步计算分析得到钒在高压下发生了从体心立方到菱面体 (Rhombohedral)的结构相变, 相变压强约70 GPa, 这一结果与最近的实验结果符合。 还首次发现当压强约380 GPa时, 将会发生菱面体到体心立方的结构相变, 这有待实验的验证。We have studied the structure phase transition of Vanadium under high pressures by density function theory. A mechanical instability in the shear elastic constant (C44) has been found for body centred cubic(bcc) Vanadium at about 95 GPa, which indicates the existence of the structural transition. By calculation and analysis, we found that there was a bcc rhombohedral structure transition at the 70 GPa, which is consistent with the experiment data. Our calculations also firstly gave that there was a rhombohedral bcc structure transition at about 380 GPa, which needs to be verified by the experiment. 相似文献
2.
Krasilnikov OM Vekilov YK Mosyagin IY Isaev EI Bondarenko NG 《J Phys Condens Matter》2012,24(19):195402
The elastic phase transitions of cubic metals at high pressures are investigated within the framework of Landau theory. It is shown that at pressures comparable with the magnitude of the bulk modulus the phase transition is connected with the loss of stability relative to uniform deformation of the crystalline lattice. Discontinuity of the order parameter at the transition point and its equilibrium value are expressed through the second-?to fourth-order elastic constants. The second-,third-?and fourth-order elastic constants and phonon dispersion curves of vanadium under hydrostatic pressure are obtained by first-principles calculations. Structural transformation in vanadium under pressure is studied using the obtained results. It is shown that the experimentally observed at P?≈?69?GPa phase transition in vanadium is the first-order phase transition close to a second-order phase transition. 相似文献
3.
The equation of state of a face-centered cubic phase has been quantitatively analyzed in terms of the statistical theory of
crystals. It has been shown that, for xenon at room temperature, the pressure equal to 1.5 GPa determines the instability
point where the condition of the positive bulk modulus of a face-centered cubic crystal is violated. A “universal line” bounding
the thermodynamic stability region of the face-centered cubic phase of van der Waals crystals has been constructed. An analysis
of the data available in the literature allows the conclusion that the revealed transition of face-centered cubic xenon to
the martensitic phase at a pressure of 1.5 GPa and a temperature of 300 K can be considered a manifestation of the predicted
instability. In this respect, it is important to perform detailed experiments on polymorphic transformations of real xenon
(and also krypton). Another aspect of the proposed theory is that it provides a means for quantitatively predicting the characteristics
of the so-called “cold” (at negative pressures) melting, which recently has become accessible for experimental observation. 相似文献
4.
V. P. Glazkov D. P. Kozlenko B. N. Savenko V. A. Somenkov G. F. Syrykh A. S. Telepnev 《Journal of Experimental and Theoretical Physics》2002,94(6):1134-1139
The vibrational spectra of NH4Cl at pressures of up to 2.6 GPa and of NH4Br at pressures of up to 7 GPa are investigated by the method of inelastic incoherent scattering of neutrons. It is found that a linear baric dependence of a librational mode changes its slope above the pressure of transition from a disordered cubic phase into an ordered cubic phase with a CsCl-type structure. The slope of the baric dependence of the transverse optical translational mode remains invariant. Estimates for the Grüneisen parameters are presented and the shape of the potential function is calculated in the one-dimensional approximation for librational vibrations in disordered and ordered cubic phases with a CsCl-type structure. It is shown that the phenomena observed are attributed to the high anharmonicity in the disordered phase. 相似文献
5.
基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0—20GPa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构.在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机理.结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3GPa,而由弹性常数判据得到的相变压强为11.52GPa,但在9.5GPa左右并没有发现简单立方相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献. 相似文献
6.
First-principles plane-wave pseudopotential approaches were used to investigate the structural phase transition of As from the rhombohedral structure to the simple cubic (sc) one under high pressure at the transition pressure of 22 GPa, which is also found to be accompanied by a volume reduction of 0.8%. The detailed structural changes during the phase transition were analyzed. 相似文献
7.
A. G. Ivanova I. A. Troyan D. A. Chareev A. G. Gavriliuk K. V. Frolov S. S. Starchikov A. O. Baskakov M. Mezouar I. S. Lyubutin 《JETP Letters》2017,106(10):662-666
Synchrotron X-ray diffraction studies of the structure of SnTe have been performed at room temperature and high pressures under the conditions of quasihydrostatic compression up to 193.5 GPa created in diamond anvil cells. Two structural phase transitions have been detected at P ≈ 3 and 23 GPa. The first phase transition is accompanied by a stepwise decrease in the volume of the unit cell by 4% because of the orthorhombic distortion of the initial SnTe-B1 cubic structure of the NaCl type. It has been found that two intermediate rhombic phases of SnTe with the space groups Cmcm and Pnma coexist in the pressure range of 3–23 GPa. The second phase transition at 23 GPa occurs from the intermediate rhombic modification to the SnTe-B2 cubic phase with the CsCl structure type. This phase transition is accompanied by an abrupt decrease in the volume of the unit cell by 8%. The pressure dependence of the volumes per formula unit at room temperature has been determined. 相似文献
8.
Haibo Xiao Ruilong Wang Linfang Xu Fujun Yang Changping Yang 《Physics letters. A》2018,382(4):224-230
First-principles calculations are performed to investigate pressure effects on structure, magnetism, martensitic phase transition and Curie temperatures of Mn2PtGa Heusler alloy in framework of the density functional theory. It is shown that Mn2PtGa prefer to crystallize in the inverse Heusler type structure. Besides, we predict an extraordinary occurrence of pressure induced metallic ferrimagnetism to half-metallic ferromagnetism transition in cubic phase of Mn2PtGa alloy under hydrostatic pressure up to 43 GPa and the half-metallic ferromagnetism is found to be robust even the lattice further compression to 90 GPa. However, with the pressure up to 100 GPa, the spin-down gap starts to close and the half metallicity begin to disappear, while with the pressure increasing from 100 GPa to 300 GPa, the alloy returns to metallic characteristic. In addition, the energy difference between the austenitic and martensitic phases is found to increase with increasing pressure followed by a decrease when pressure reaches to 43 GPa, which implies a variation trend of martensitic phase transition temperature. Furthermore, Curie temperatures in both austenitic and martensitic phases are estimated under pressure by using the standard mean-field approximation which agrees well with the theoretical results in literature. The robustness of the half metallicity, magnetic transition and the high Curie temperature under pressure make Mn2PtGa alloy a promising candidate for applications in spintronic devices. 相似文献
9.
The Raman studies of lead zirconate titanate with varied grain size from 27.5 nm to 983 nm were performed under pressure up to 32 GPa to elucidate the scenario of phase transition pressures of lead zirconate titanate, which lies in the morphotropic phase boundary. The coexistence of ferroelectric rhombohedral and tetragonal phases at ambient condition changed to the coexistence of tetragonal and cubic phases at intermediate pressure and finally, transited to paraelectric cubic phase at elevated pressure. The pressure evolution of Raman spectra results indicated that the phase transition pressure increased with the reduction of the particle size. 相似文献
10.
Bo Kong Bo Zhu Yan Cheng Lin Zhang Qi-Xian Zeng Xiao-Wei Sun 《Physica B: Condensed Matter》2011,406(15-16):3003-3010
The structural, mechanical, thermodynamics properties and phase transition of FeVSb are investigated extensively using the first principle calculations and the quasi-harmonic Debye model. From the calculated elastic constants of cubic FeVSb, some other mechanical quantities, such as bulk modulus and Poisson's ratio, are drawn. Surprisingly, it is found that almost all these mechanical quantities are larger than those of CoVSb (Bo Kong et al., J. Alloys Compd. 509 (2011) 2611); the obtained corresponding transition pressure from fcc to hcp is also larger than that of CoVSb. For these distinctions, their complete different electronic and magnetic behaviors in their cubic structures may be responsible. However, in their hexagonal structures, atomic configurations are similar in terms of the analysis of both the ground-state structure and enthalpy–pressure curves. It is also shown that the elastic instability of cubic FeVSb does not appear with pressure up to 120 GPa and should not be a reason for the pressure-induced phase transition. In addition, heat capacity, Debye temperatures, and so on are obtained successfully for cubic FeVSb under the quasi-harmonic Debye model. Furthermore, we attempt to explore the phase diagram of FeVSb with the model. 相似文献
11.
12.
O. M. Krasil’nikov Yu. Kh. Vekilov E. I. Isaev N. G. Bondarenko 《Journal of Experimental and Theoretical Physics》2011,112(2):240-245
Structural transformations in elementary metals under high pressures are considered using the Landau theory of phase transitions,
in which the finite strain tensor components play the role of the order parameter. As an example, the phase transition in
vanadium observed at a pressure of 69 GPa is analyzed. It is shown that it is a first-order elastic phase transition, which
is close to a second-order transition. 相似文献
13.
U.L.C. Hemamala D.V.S. Muthu A.M. Krogh Andersen L. Ouyang 《Solid State Communications》2007,141(12):680-684
The room-temperature Raman and infrared spectra of zirconium vanadate (ZrV 2O7) were observed up to pressures of 12 GPa and 5.7 GPa, respectively. The frequencies of the optically active modes at ambient pressure were calculated using direct methods and compared with experimental values. Average mode Grüneisen parameters were calculated for the Raman and infrared active modes. Changes in the spectra under pressure indicate a phase transition at ∼1.6 GPa, which is consistent with the previously observed α (cubic) to β (pseudo-tetragonal) phase transition, and changes in the spectra at ∼4 GPa are consistent with an irreversible transformation to an amorphous structure. 相似文献
14.
15.
Pallavi Teredesai N. Chandrabhas V. Vijayakumar R.S. Rao S.K. Sikka 《Solid State Communications》2004,129(12):791-796
High pressure Raman and angle dispersive X-ray diffraction (ADXRD) measurements on the metallic hexaboride LaB6 have been carried out upto the pressures of about 20 GPa. The subtle phase transition around 10 GPa indicated in Raman measurements is confirmed by ADXRD experiments to be a structural change from cubic to orthorhombic phase. Ab-initio electronic band structure calculations using full potential linear augmented plane wave method carried out as a function of pressure show that this transition is driven by the interception of Fermi level by electronic band minimum around the transition pressure. 相似文献
16.
Static-compression data and absorption spectra for CsI have been collected to 61 GPa (610 kbar) at room temperature. The band gap closes with increasing pressure and CsI is expected to metallize at 105 (± 15) GPa. A second order phase transition to the CuAu I structure is observed at 39 (± 1) GPa. The elastic constants measured at low pressures do not predict that an elastic instability, and hence a structural distortion, would occur at elevated pressures. Similarly, an ionic pair-potential model which reproduces the properties of CsI at low pressures does not show the distortion to be stabilized at high pressures. 相似文献
17.
V. P. Glazkov D. P. Kozlenko B. N. Savenko V. A. Somenkov 《Journal of Experimental and Theoretical Physics》2000,90(2):319-323
The vibrational spectra of ammonium iodide NH4I at pressures up to 4.1 GPa and ammonium fluoride NH4F at pressures up to 4.7 GPa were investigated by inelastic incoherent neutron scattering. The pressure dependences of the transverse optical translational and librational modes were obtained. The behavior of the rotational potential barrier for the ammonium ion as a function of the lattice parameter for disordered and ordered cubic phases of ammonium halides with CsCl type structure were calculated. The results obtained confirm that the transition from an orientationally disordered cubic phase into an ordered cubic phase in ammonium halides occurs at close critical values of the positional parameter of hydrogen (deuterium). 相似文献
18.
We studied the structural and electronic properties of carbon
nanotubes under hydrostatic pressures based on molecular dynamics
simulations and first principles band structure calculations. It is
found that carbon nanotubes experience a hard-to-soft transition as
external pressure increases. The bulk modulus of soft phase is two
orders of magnitude smaller than that of hard phase. The band
structure calculations show that band gap of (10, 0) nanotube
increases with the increase of pressure at low pressures. Above a
critical pressure (5.70GPa), band gap of (10, 0) nanotube drops
rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge
density shows that a large pressure can induce an
{sp}2-to-{sp}3 bonding transition, which is confirmed by
recent experiments on deformed carbon nanotubes. 相似文献
19.
本文采用基于密度泛函理论(DFT)的第一性原理方法对ZnO晶体在c轴取向压力作用下的晶体结构、电子结构的变化进行了研究. 结果表明,当压力在0到6 GPa区间时,晶格参数呈线性变化,带隙随压力增大而增大,显示弹性应变特征;当压力从6 GPa增大到10 GPa的过程中,晶体结构有了较大变化,出现了介于常压下纤锌矿结构和等静压高压下NaCl结构之间的类石墨结构(Graphitelike structure). 伴随着这一结构相变,ZnO的晶格参数,能隙和态密度等电子结构出现了较大跃变. 相似文献
20.
本文采用基于密度泛函理论(DFT)的第一性原理方法对ZnO晶体在c轴取向压力作用下的晶体结构、电子结构的变化进行了研究.结果表明,当压力在0~6 GPa区间时,晶格参数呈线性变化,带隙随压力增大而增大,显示弹性应变特征;当压力从6 GPa增大到10 GPa的过程中,晶体结构有了较大变化,出现了介于常压下纤锌矿结构和等静压高压下NaCl结构之间的类石墨结构(Graphitelike structure).伴随着这一结构相变,ZnO的晶格参数,能隙和态密度等电子结构出现了较大跃变. 相似文献