高压物理学报

Structural Transition and Raman Scattering of ZnSe Nanoribbons under High Pressure

JIN En-Ji, YAO Li-De, WANG Fei-Fei, SHEN Xi, YOU Shu-Jie, YANG Liu-Xiang, JIANG Sheng, LI Yan-Chun, et al.

2009, 23(4): 241-246 . doi: 10.11858/gywlxb.2009.04.001

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Abstract:
Structural stability of ZnSe nanoribbons was analyzed by means of high pressure in situ angular dispersive X-ray diffraction(ADXD). The pressure induced structural transition from the Zinc blende (ZB) to a rocksalt (RS) phase occurs at about 12.6 GPa, and at the transition point the relative volume reduction is close to 13%. By fitting the relative volume-pressure relation to the Birch-Murnaghan equation of states, the bulk modulus B0 for the ZB and RS phases were determined. The values of B0 are 56 GPa (B0=4) and 116 GPa (B0=4) for the former and the latter, respectively. According to the measured high-pressure Raman scattering spectra, the TO phonon modes split into two peaks at about 5.5 GPa, and the LO peak gradually disappears above 12.8 GPa due to the semiconductor-metal transition. Using the value of the bulk modulus obtained from the ADXD experiments, the corresponding mode Grneisen parameters are obtained for the ZB phase.

Fine Structure of Fe-Based Metal Film Interface and Diamond Single Crystal Growth

TIAN Bin, XU Bin, QI Yong-Xin, LI Mu-Sen, LI Li

2009, 23(4): 247-251 . doi: 10.11858/gywlxb.2009.04.002

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Abstract:
Field emission scanning electron microscope (FESEM) has been used to investigate the fine structure of Fe-based metal film interface and its crosssection. It is shown that nanoscale pyramid cone shapes are found on the metal film interface (100), serrate steps are found on the metal film interface (111), and cystiform shapes with terrace structure are found on the cross-section near the catalyst. Other faults have brittleness fracture characteristic with nanoscale clusters are found on the fault surface. It is proposed that the different morphologies of the metal film have relations with catalyzing mechanism. The brittleness fracture characteristic of the cross-sectionon might be due to the carbide existence, and the nanoscale particles should be eutectic carbides.

Effect of Tensile Stress on Exchange Bias in Ferromagnetic/Antiferromagnetic Bilayers

BAI Yu-Hao, YUN Guo-Hong, Narisu

2009, 23(4): 252-260 . doi: 10.11858/gywlxb.2009.04.003

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Abstract:
Based on the principle of minimal energy and Stoner-Wohlfarth model, the effect of the tensile stress on the exchange bias for ferromagnetic/antiferromagnetic bilayers has been investigated. When the applied field is absent, according to the relation between the energy of the system and the orientation of ferromagnetic magnetization, the location of the intrinsic easy axes and intrinsic hard axes of the system have been obtained. It is found that the system will be in monostable state or bistable state, which is controlled by the competition between the uniaxial anisotropy and the exchange anisotropy of the system. Monostable state and bistable state of the system determine the angular dependence of exchange bias immediately. When the applied field is parallel to the intrinsic easy axes and intrinsic hard axes, by analyzing the magnetization process, we find that one of the switching field of the hysteresis loop shows a jump, while the other is kept constant, and consequently the exchange bias field and the coercivity will appear a step. Both the exchange bias field and the coercivity have a greater value at the point of step. The numerical calculations indicate that both the magnitude and the orientation of the tensile stress will significantly affect the exchange bias by making a transition between monostable state and bistable state in the system. This transition induces a significant change in angular dependence of the exchange bias. Our results demonstrate that tensile stress is a viable way to control and tune the exchange bias of the ferromagnetic/antiferromagnetic bilayers.

Numerical Simulation of the Motion of Flyer Driven by Slab Explosive Initiated at Centered Point

JIANG Yang, SUN Cheng-Wei, LI Ping, BAI Jin-Song

2009, 23(4): 261-265 . doi: 10.11858/gywlxb.2009.04.004

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Abstract:
In order to study the characteristics of flyer's acceleration by divergent detonation wave, a 2D numerical code TDY2D was developed. By using the equation of state of detonation products which are got by computing for the experimental models, the TDY2D is used to compute the motion of flyers driven by slab charge that initiated at centered point for three experimental models which are three kinds of explosive-flyer assemblies with different length/diameter ratio. The simulation results about the velocity of some points on the flyers and the front surface shape of the flyers impacting on target agree well with the experimental data. The precision in calculation is high. These prove that the code TDY2D is correct and effective.

Compression Isentropes of Copper and Aluminum under 40 GPa

WANG Gui-Ji, TAN Fu-Li, SUN Cheng-Wei, ZHAO Jian-Heng, WANG Gang-Hua, MO Jian-Jun, ZHANG Ning, WANG Xiao-Song, WU Gang, HAN Mei

2009, 23(4): 266-270 . doi: 10.11858/gywlxb.2009.04.005

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Abstract:
Using the magnetically driven apparatus CQ-1.5 developed by us, compression isentropes of copper T1, LY12 aluminum, and pure aluminum L1 are measured up to 40 GPa by Doppler pins system (DPS) and Velocity Interferometer System for Any Reflectors (VISAR), respectively. The experimental compression isentropes are compared with the theoratical compression isentropes based on Grneisen equation of state (EOS) and shock Hugoniot data. The results show that the experimental compression isentropes are consistent with the theoretical compression isentropes within a maximum deviation of 3%, and approach to and lie below the shock Hugoniot curves under 40 GPa. The results show that the experimentally measured results are correct and reliable.

Modification of Tuler-Butcher Model with Damage Influence

JIANG Dong, LI Yong-Chi, GUO Yang

2009, 23(4): 271-276 . doi: 10.11858/gywlxb.2009.04.006

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Abstract:
A modificatin of Tuler-Butcher model including damage influence was presented, which was incorporated into a hydrodynamic one-dimensional finite difference computer code, to simulate the process of spall fracture of 45 steel and Al-Li alloy. The calculated results are in good agreement with experimental data, and shows the correctness of the model.

Application Research on JWL Equation of State of Detonation Products

ZHAO Zheng, TAO Gang, DU Chang-Xing

2009, 23(4): 277-282 . doi: 10.11858/gywlxb.2009.04.007

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Abstract:
By investigating the JWL equation of state of detonation products of condensed explosive, we present a method to determine JWL parameters by fitting. This approach does not require cylinder test and is more economical, secure, convenient and accurate than existing methods. Using this method, four kinds of common explosive, e.g., TNT, C-4, PETN and HMX have been studied. By comparing to the p-V curve of JWL equation of state given by cylinder test, we showed that the fitting has a high precision and meets the need of explosion mechanics application.

Experimental Study on Dynamic Behavior of Lead Plate Driven by Two Head-on Colliding Detonation Waves

ZHANG Chong-Yu, HU Hai-Bo, LI Qing-Zhong, YUAN Shuai

2009, 23(4): 283-287 . doi: 10.11858/gywlxb.2009.04.008

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Abstract:
In order to investigate the configuration and mass distribution of collision bulging, dynamic behaviors of Pb plate driven by collision of head-on sliding detonation waves were characterized with high-speed frame photography and pulsed X-ray radiography. Experimental results showed that a bulging similar to a shaped charge jet were produced in the collision region, which appeared as a multi-zone structure across several layers. The tip of bulging with higher velocity had a characteristic of fragmentary and cavitation because of its speed gradient and the interaction with air, and its bulk density was much lower than the pre-shock initial density of Pb. Though the root of bulging had a lower velocity and a higher density relatively, it was also in non-dense state. It suggested that the collision of sliding detonation waves, strength of materials and shock melting might play a leading role in the bulging formation process.

Analytic Equation of State for Generalized Morse Potential Fluid and Application to N2 Fluid

XUE Xin-Ying, SUN Jiu-Xun, TIAN Rong-Gang

2009, 23(4): 288-298 . doi: 10.11858/gywlxb.2009.04.009

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Abstract:
The analytic expressions for equation of state (EOS) and thermodynamic properties have been derived for the generalized Morse (GM) potential fluids, by using the Ross variational perturbation theory and the analytic Percus-Yevick (PY) expression of radial distribution function of hard spheres. Extensive comparison of the numerical results with computer simulations shows that the precision of the analytic Ross theory is equivalent to or slightly better than the non-analytic modified Weeks-Chandler-Anderson (mWCA) theory, and is much better than the complicated optimized reference hyper-netted chain (RHNC) theory. This analytic expressions for equation of state have been applied to N2 fluid at ambient temperature and low pressure (below 1 GPa) with the parameters of the generalized Morse potential are obtained by fitting to experimental data, results of prediction of the pressure above 1 GPa validate the analytic EOS with good agreement within a wide range of pressure and temperature.

Effects of High Pressure Treatment on Structures and Luminescence Properties of Nano ZnO and Composite ZnO/SnO2 Materials

SUN Zhen-Ya, WANG Shuo, DENG Yun-Di, LI Ming-Fa

2009, 23(4): 299-304 . doi: 10.11858/gywlxb.2009.04.010

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Abstract:
The nano ZnO and nano composite ZnO/SnO2 materials were prepared by sol-gel method, then the prepared specimens were treated by high pressure method of which the pressure is up to 6 GPa. X-ray diffraction (XRD) and transmission electron microscopy (TEM) and photoluminescence spectrometer were employed to study structures and luminescence properties of the specimens. The results indicate that the particle sizes of ZnO and ZnO/SnO2 decrease 5.9% and 26.3% respectively after high pressure treatment. And the photoluminescence spectra show that photoluminescence spectra intensity of nano ZnO and composite ZnO/SnO2 materials both reduce after high pressure treatment, but the reduced intensity of composite ZnO/SnO2 materials is less than the one of pure ZnO, and the possible reasons are discussed.

Raman Scattering Studies of n-Octane under High Pressure

WU Xiao-Xin, LI Min, LI Fang-Fei, ZHOU Qiang, GAO Wei, CUI Qi-Liang, ZOU Guang-Tian

2009, 23(4): 305-309 . doi: 10.11858/gywlxb.2009.04.011

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Abstract:
High pressure Raman spectra of n-octane were investigated by diamond anvil cell (DAC) at pressure up to 7 GPa and ambient temperature. The result shows that the liquid-solid phase transition of n-octane takes place around 0.8 GPa. Within the experimental pressure range, the Raman shift of n-octane moves to higher frequency, while the peak intensity decreases, and the width of peaks broaden with increasing pressure. A turning point is observed in the curve of pressure-dependent Raman shift when the pressure increases up to 6.8 GPa. This result indicates that a solid-solid phase transition for n-octane has been finished at this pressure. The pressure-induced phase transition pressure in alkanes decreases with the length of their chains increasing.

Molecular Dynamics Simulation of Water under Superhigh Pressure

ZHOU Xiao-Ping, YANG Xiang-Dong, LIU Jin-Chao

2009, 23(4): 310-314 . doi: 10.11858/gywlxb.2009.04.012

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Abstract:
Thermodynamic properties and structure of water under superhigh pressure were investigated by Equilibrium Molecular Dynamics (EMD) simulations. The obtained heat of vaporization and self-diffusion coefficient are in good agreement with the experimental data. With the increase of pressure, the hydrogen bond strength between water molecules increases, while self-diffusion coefficient decreases. With the increase of temperature, the hydrogen bond strength between water molecules decreases, while self-diffusion coefficient increases. However in the supercooled water, self-diffusion coefficient increases with the increase of temperature.

Experimental Studies on Hugoniot Data of Methane-Air Mixtures under Shock Compression

WANG Xiao-Yan, HUA Jing-Song, WEN Shang-Jie, JIN Shan, SUN Xue-Lin

2009, 23(4): 315-320 . doi: 10.11858/gywlxb.2009.04.013

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Abstract:
To study the state parameters of methane-air mixture under shock compression, Aluminum target chamber filled with methane-air mixture were impacted by tungsten alloy projectiles. Projectiles were accelerated to about 5 km/s using a two-stage light gas gun. Methane-air mixture with different air ratioes of 0, 1%, 5%, and 10% were tested, respectively. The radiance signals from shocked methane-air gases were recorded by an instantaneous pyrometer system. The Hugoniot data of four mixed ratio gases were obtained. The experimental results indicated that the shock temperatures of mixtures increase with rising of the air mixed ratio. The mixtures emitted non-equilibrium thermal radiation in shock downstream. The ionization of methane-air gas with 10% air mixed ratio is calculated by Saha ionization function. Calculated results indicated that methane-air mixed gases with an air mixed ratio less than 10% doesn't ionize, and can protect pins effectively.

2009 Vol. 23, No. 4

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