高压物理学报

Electronic Behaviors of the Rocksalt and Monoclinic AgCl under Pressure

WANG Zuo-Cheng, CHE Li-Xin, LI Yan, CUI Tian, ZHANG Miao, NIU Ying-Li, MA Yan-Ming, ZOU Guang-Tian

2007, 21(3): 225-230 . doi: 10.11858/gywlxb.2007.03.001

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Abstract:
The structural behavior and the electronic properties of AgCl under pressure are extensively studied by using the pseudopotenial plane-wave method and generalized gradient approximation within density functional theory. The theoretical transition pressure corresponding to the phase transition from rocksalt to monoclinic structure is obtained from the enthalpy calculations. The location of the valence band maximum and the conduction band minimum in the entire Brillouin zone are predicted for both structures. The rocksalt and monoclinic phase of AgCl are both semiconductors with indirect gap and the variations of the band gaps with pressure indicate that they do not become metallization before structural instability. Furthermore, the bonding between Ag and Cl atoms becomes less ionic or more covalent under compression.

Experimental Studies on Air Drag Coefficient of Spherical Tungsten Fragments

TAN Duo-Wang, WANG Guang-Jun, GONG Yan-Qing, GAO Ning

2007, 21(3): 231-236 . doi: 10.11858/gywlxb.2007.03.002

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Abstract:
The air drag coefficients of spherical tungsten fragments are studied. The fragment includes ideal sphere and real fragment formed by a warhead. The experimental results show that: (1) for ideal spheres, the attenuation coefficient of velocity is constant, the air drag coefficient is slightly affected by the initial velocity and is a linear function of initial velocity, and (2) for real fragments formed by a warhead, the flight performances are different from ideal spheres, the air drag coefficient is affected by the flight velocity and is a linear function of flight velocity.

Synthesis and Characterization of h-BCN Nanocrystallite under High-Pressure and High-Temperature

LI Xue-Fei, ZHANG Jian, SHEN Long-Hai, YANG Da-Peng, CUI Qi-Liang, ZOU Guang-Tian

2007, 21(3): 237-241 . doi: 10.11858/gywlxb.2007.03.003

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Abstract:
h-BCN compounds were synthesized with C3H6N6 and B2O3 as raw materials, combined with heat treatment, high pressure and high temperature. An amorphous BCN precursor was prepared at 1 100 K under vacuum. Annealed for 30 min, at 1 500 K under 5.0 GPa, the amorphous BCN precursor crystallizes into hexagonal BCN compound with lattice constants of a=0.250 5 nm, c=0.665 9 nm determined by using the reflex module combined in the Materials Studio program analysis. The shape and SAD of sample also approved that the sample was h-BCN crystal by TEM analysis. The grain size about was 200 nm. XPS analysis was applied for the sample. The results confirmed bending energy of CC, CN, CB, NB. It indicated atom level chemical combination of BCN. The composition and content of the sample were analyzed by EDX.

Study on Penetration of Concrete Targets by Ogive-Nose Steel Projectile

ZHOU Ning, REN Hui-Qi, SHEN Zhao-Wu, HE Xiang, LIU Rui-Chao

2007, 21(3): 242-248 . doi: 10.11858/gywlxb.2007.03.004

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Abstract:
We conducted acceleration-time measurement of penetration experiments in targets with 100 mm diameter, 4.0 caliber-radius-head, 25 kg projectiles. The 3 m3 m3m and 2 m2 m2m concrete targets had an nominal unconfined compressive strength of 35 MPa and density 2 450 kg/m3. Projectiles were designed to contain a single-channel acceleration data recorder, so we recorded accelerations in the bore of the gun and accelerations during the penetration event. A 100 mm diameter powder gun launched the 25 kg projectiles to striking velocities between 310 and 632 m/s. We compared the measured penetration depths and acceleration-time data with the calculated results using Forrestal formula. The calculated results are in good agreement with rigid-body acceleration measurements for the rise times and peak plateau responses. The acceleration-time data of projectiles can be helpful for devising armour-piercing projectile and defense engineering.

Structure and Ferroelectric Properties of Dense Nanocrystalline BaTiO3 Ceramics Prepared by High Pressure Sintering Method

LI Peng-Fei, JIN Chang-Qing, XIAO Chang-Jiang, PAN Li-Qing, WANG Xiao-Hui

2007, 21(3): 249-252 . doi: 10.11858/gywlxb.2007.03.005

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Abstract:
Dense nanocrystalline BaTiO3 ceramics with a grain size of 50 nm were prepared under 6 GPa at 1 000 ℃ using a high pressure sintering method. The sintered bulk is uniform and the relative density is above 97%. We annealed the ceramic samples in oxygen to eliminate the oxygen vacancies caused by high pressure. After anneal, several broadened peaks were observed through dielectric measurements. However, these peaks are very different from those of coarser-grained ceramics. The observation of polarization hysteresis loop provides the solid evidence of ferroelectricity in these nano-sized BaTiO3 ceramics. It is believed that the absence of 90 domains and the existence of depolarization field caused by nonferroelectric grain boundaries contribute to the slim loop.

An Improved of Experimental Hypervelocity Launcher and Simulation

BAI Jing-Song, TANG Mi, HUA Jing-Song, LI Ping, TAN Hua

2007, 21(3): 253-258 . doi: 10.11858/gywlxb.2007.03.006

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Abstract:
A numerical simulation method for calculation of the three-stage light-gas gun impacts on launch flier to hypervelocity is presented. Based on multi-fluid volume of fraction (VOF) and parabolic piecewise method (PPM), a multi-fluid parabolic piecewise method (MFPPM) shock wave physics code is developed to calculate the experimental hypervelocity launchers. To verify and validate our code of MFPPM, some experimental hypervelocity launchers from Sandia National Laboratories are simulated, and the numerical results of flier velocity are excellent in agreement with that experiment (the maximal relative error is 1.07%). Experiment and simulation results of our experiment on the three-stage light-gas gun are given (the maximal relative error is 1.04%). To satisfy well of the high-pressure equation of state (EOS) data measurement, an improved design model from the computation is presented.

Investigation of in Situ Raman Spectrum and Electrical Conductivity of PbMoO4 at High Pressure

YU Cui-Ling, YU Qing-Jiang, GAO Chun-Xiao, LIU Bao, HE Chun-Yuan, HUANG Xiao-Wei, HAO Ai-Min, ZHANG Dong-Mei, CUI Xiao-Yan, LIU Cai-Long, et al.

2007, 21(3): 259-263 . doi: 10.11858/gywlxb.2007.03.007

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Abstract:
PbMoO4, with high acousto-optic figure of merit, low acoustic loss and nicer acoustic impedance matching, has received much attention because of applications as acousto-optic deflector, modulator, adjustable filter, suface acoustic wave devices and great potential to act as an effective low-temperature scintillator for nuclear instrumental applications. In this study, in situ Raman spectrum of PbMoO4 was measured in a diamond anvil cell (DAC). The electrical conductivity measurement of PbMoO4 was performed at different pressure and temperature. All Raman peaks disappeared at 12.5 GPa, which indicated that the PbMoO4 experienced gradually the crystal to amorphous transition between 10.8 GPa and 12.5 GPa. Upon decompresstion from 26.5 GPa to 9.4 GPa a broad Raman peak occurred at a low frequency,while the peak of 858 cm-1 occured at 2.4 GPa again, thus suggesting that the PbMoO4 crystal was gradually recovered from the amorphous state. Above 10.8 GPa, the electrical conductivity of PbMoO4 increased obviously with increasing temperature and pressure.

Investigation of Phase Transitions of ZrO2 under High-Pressure and High-Temperature Conditions by Raman Spectroscopy

ZHANG Hong, XIAO Wan-Sheng, TAN Da-Yong, LUO Chong-Ju, LI Yan-Chun, LIU Jing

2007, 21(3): 264-268 . doi: 10.11858/gywlxb.2007.03.008

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Abstract:
Using argon as a pressure medium, the phase transitions of monoclinicstructured ZrO2 under high-pressure and high-temperature have been investigated by means of in situ Raman spectra method and a laser-heated diamond anvil cell (DAC). At room temperature, the baddeleyite-type ZrO2 begins to transform to a new phase at 3.4 GPa, Raman bands from the new phase become prominent at 10.4 GPa, and this new high-pressure structure retains up to 15.3 GPa, the highest pressure before heated. The new phase has been identified as Pbca phase. Raman spectrum of Pbca phase is presented for the first time based on our experiments. At pressure of 15.3 GPa the Pbca phase was heated by YAG laser to about 1 000~1 500 ℃, and then it transforms to a PbCl2 phase. This phase is stable up to 23 GPa, the highest pressure in this study.

Modified Einstein Model to Consider Thermal Effect and Applied to Three Universal Equations of State

ZHANG Chao, SUN Jiu-Xun, TIAN Rong-Gang, LI Ming

2007, 21(3): 269-278 . doi: 10.11858/gywlxb.2007.03.009

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Abstract:
The Einstein model to consider thermal effect in universal equations of state (UEOS) is modified. It is proposed that the zero-point vibration term should be deleted in a thermal UEOS, and the parameters can not be directly taken as experimental data at a reference temperature, VR, BR, BR and GR, but their values at absolute zero temperature, V0, B0, B0 and G0. An approach is proposed to solve V0, B0, B0 and G0 from VR, BR, BR and GR. The approaches are applied to three typical universal EOSs, including the Baonza, mMNH and Vinet EOSs. The numerical results show that the solved values of parameters are almost identical for different EOSs. And the thermo-physical properties predicted through different EOSs are almost identical at zero and low-pressure conditions, once the same approach and input experimental data are used to solve parameters. It is concluded that the prediction of thermo-physical properties at zero and low-pressure conditions cannot be taken as the criteria to judge the applicability of a universal EOS.

Energy Dispersive X-Ray Powder Diffraction of Natural Enstatite under High Pressure Conditions

MA Mai-Ning, ZHOU Wen-Ge, LIU Jing, LI Yan-Chun, LI Xiao-Dong

2007, 21(3): 279-282 . doi: 10.11858/gywlxb.2007.03.010

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Abstract:
Using synchrotron radiation and diamond anvil cell (DAC) in high pressure research station of Beijing Synchrotron Radiation Facility (BSRF), energy dispersive X-ray powder diffraction (EDXD) of the natural enstatite collected from Damapin in Hebei Province, have been in situ measured under room temperature and high pressure (0~31.64 GPa) conditions. Then the unit-cell parameters of sample and their changes versus pressure have been acquired using the UnitCell software. Furthermore, basing on Murnaghan equation of state (EOS), bulk modulus KT(0)=172 GPa, compression coefficient, and p-V equation of state of natural enstatite have been obtained. The experiment data show that compression coefficient have distinct anisotropy for the three crystallographic axis. This result is consistent with the anisotropy of elastic velocity of orthopyroxene.

Phase Evolution of Zr-Based Bulk Metallic Glass Prepared by Shock-Wave Quenching under High Temperature and High Pressure

YANG Chao, CHEN Wei-Ping, ZHAN Zai-Ji, JIANG Jian-Zhong

2007, 21(3): 283-288 . doi: 10.11858/gywlxb.2007.03.011

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Abstract:
Phase evolution (PH) of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) prepared by shock-wave quenching has been studied under high-temperature and high-pressure using in situ synchrotron radiation energy-dispersive X-ray diffraction. The results show that the primarily precipitated phase is Zr2Be17 at applied pressures, but the subsequent PH processes are different. The crystallization temperature increases with pressure, but with a sudden drop at about 6.0 GPa. Compared with experimental results of the BMG prepared by water quenching, it can be concluded that crystallization temperature of the BMGs prepared by shock-wave quenching and water quenching all drop at the same pressure region, at which their PHs are different from those of other pressures. The different PHs and the drop of crystallization temperature may be attributed to that the BMG possesses different atomic configuration at different pressures.

Constitutive Behaviors of a Silicone Rubber at High Strain Rates

LIN Yu-Liang, LU Fang-Yun, LU Li

2007, 21(3): 289-294 . doi: 10.11858/gywlxb.2007.03.012

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Abstract:
Silicone rubber is a macromolecule polymer, and can suffer a large deformation. The silicone rubber specimens are tested at a series of strain rates by modified Split Hopkinson Pressure Bar (SHPB) techniques. Based on the experimental data, a constitutive model of the silicone rubber is built up based on Ogden strain energy functions. An interesting phenomenon－localized damage cycle, so called lag circle－shows up in the tested specimen under high strain-rates loading. The diameters of the damage cycle are associated with strain-rate and specimen's size. A formulation about the relations between the diameter and the strain-rate, specimen's size is presented.

Chemical Synthesis and Characterization of Flaky h-CN by HPHT

YANG Da-Peng, LI Ying-Ai, DU Yong-Hui, SU Zuo-Peng, JI Xiao-Rui, YANG Xu-Xin, GONG Xi-Liang, ZHANG Tie-Chen

2007, 21(3): 295-298 . doi: 10.11858/gywlxb.2007.03.013

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Abstract:
Hexagonal boron carbonitrogen (h-BCN) crystal was synthesized from the mixture of boron powder and CNH compound prepared by pyrolysis of Melamine (C3H3N3) under high temperature (1 400~1 500 ℃) and high pressure (5.0~5.5 GPa). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to determine the product chemical composition and characterization. The results show that the product has composition of B0.18C0.66N0.16 (near BC4N) and atomic-level hybrid. X-ray diffraction analysis indicates that the powder has hexagonal network structure. Scanning electron microscopy result suggests that h-BCN crystal morphology are mainly hexagonal flaky and the diameter is about 1 m, thickness 200 nm.

First Principles Study of the Elastic, Electronic and Optical Properties of CdO under Pressure

HE Kai-Hua, ZHENG Guang, CHEN Gang, Lü Tao, WAN Miao, XIANG Dong, JI Guang-Fu

2007, 21(3): 299-304 . doi: 10.11858/gywlxb.2007.03.014

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Abstract:
The structural, elastic, electronic and optical properties of CdO under high pressure were studied by plane wave pseudo-potential method which based on the density functional theory. The generalized gradient approximation and local density approximation were used to describe the exchange-correlation potential. Comparing the lattice constants and bulk modules between experimental and computational, we can find the calculated results by local density approximation are well agreement with the experimental values. Under high pressure, the conduction bands of two structures have a shift tendency to higher energy, and the valence bands have a shift tendency to lower energy. We analyze the optical properties about the two structures associate with the partial density of states and the shifting of energy levels under high pressure.

Direct Hydrothermal Synthesis and Luminescence Property of Titanate Nanotubes Doped with Eu3+ Ions

SONG Gong-Bao, WANG Mei-Li, MIAO Lan-Dong, LI Jian, ZHANG Bao-Shu

2007, 21(3): 305-310 . doi: 10.11858/gywlxb.2007.03.015

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Abstract:
Pure titanate nanotubes and titanate nanotubes doped with Eu3+ ions were synthesized by hydrothermal method. In this process, the preparation of nanotubes is synchronously finished by doping with Eu3+ ions. The morphology, structure, thermal stability and luminescence property of titanate nanotubes were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), and photoluminescence instrument. The results show that the method is simple, stable and high-yield. The structure of the nanotube could be approximately indexed by (H,Na)2Ti3O7 or (H,Na)2(Ti,Eu)3O7. Treatment of high temperature will bring into big changes to structures of titanate nanotubes. When the calcine temperature is higher than 450 ℃, tubulous structure of titanate nanotube was destroyed and transformed into structure of anatase phase. Sample of TNT-Eu shows strong luminescence property. There exist three peaks (393.5 nm, 593 nm, 614 nm) in its luminescence spectrum which are associated to 5D0-7F1 and 5D0-7F2 Eu3+ electronic transition respectively.

Ballistic Limit Analysis for Projectiles Impacting on Dual Wall Structures at Hypervelocity

DING Li, ZHANG Wei, PANG Bao-Jun, LI Can-An

2007, 21(3): 311-315 . doi: 10.11858/gywlxb.2007.03.016

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Abstract:
The potential threat from meteoroids and orbital debris particles impacting on pressurized spacecraft prompted a study of ballistic limit analysis. The paper presents a new analytical ballistic limit equation for sphere projectiles normal impacting on thin plates. This equation applies to cases of hypervelocity impacts on dual wall structures. The developed equation is based on theoretical analysis of a perfectly elastic plastic plate. The Rayleigh-Ritz method was used. To test the validity, we predicted 30 tests by the equation. It was found that there are 24 predictions corresponding to the tests. Curve is presented for the critical projectile diameter versus the projectile velocity. The curve is in good agreement with curves that have been developed by Christiansen.

Effect of Diamond Films Thickness on Thermal Residual Stress

TANG Da-Pei, GAO Qing, WU Lan-Ying

2007, 21(3): 316-321 . doi: 10.11858/gywlxb.2007.03.017

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Abstract:
Each component of thermal residual stress in diamond films deposited onto Mo substrate was simulated and analyzed comprehensively by using the finite element method, and the different thickness (20~1 000 m) of the films was used during the simulation. The contour plots of these components distribution were obtained. In addition, the effect of the films thickness on the maximum tensile principal stress in films and on the maximum of every stress component at interface between films and substrate was investigated. The results show that the location of maximum tensile principal stress in the films is at the upward face or side face of the films or the interface, and the magnitude of it increases when the films become thicker. Also, the maximum axial stress at the interface increases when the films become thicker whereas the maximum compressive radial stress, maximum compressive circular stress and maximum shear stress at the interface are in reverse, and the reduction extent of the maximum shear stress is small. The increase or reduction rate of each stress mentioned above is slower when the films thickness becomes larger. These conclusions are useful to choose rationally films thickness and to control effectively the stresses during preparation of diamond films.

Study on the Mechanism of PZT95/5 Powder Synthesis by Shock Waves

WANG Jun-Xia, YANG Shi-Yuan, HE Hong-Liang, WANG Jin

2007, 21(3): 322-326 . doi: 10.11858/gywlxb.2007.03.018

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Abstract:
A cylinder shock-wave recycling device was used, and via impacting effects of explosive shock waves, PZT95/5 powders were synthesized from a mixture of Pb3O4, ZrO2, and TiO2 oxides. Based on the XRD analyses of recovered powders and shock wave theory, the synthesis mechanism and process of PZT powders are discussed from the experimental and theoretical facets. The results show that PZT synthesis and Pb3O4 decomposition happened simultaneously, because of the shock-wave particularity, the system temperature and pressure could simultaneously satisfy the thermodynamics conditions of Pb3O4 decomposition and PZT synthesizing reactions. Thus once PbO formed by decomposing Pb3O4, PbO would react immediately with ZrO2 and TiO2 oxide compounds to produce PZT. And the reaction of shocksynthesizing PZT powders belonged to the special solid phase reaction, in which the diffusion velocity and reaction speed were enhanced greatly.

Experimental Validation of Quasi-Elastic Response of Metal during Reloading Process

SONG Ping, ZHOU Xian-Ming, YUAN Shuai, LI Jia-Bo, WANG Xiao-Song

2007, 21(3): 327-331 . doi: 10.11858/gywlxb.2007.03.019

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Abstract:
An uniaxial strain experiment of a magnesium alloy (brand:MB2) disk under shock loading and reloading was designed by a wave reflection method. Time-resolved interfacial velocity between the MB2 sample and a LiF window was measured by a VISAR (Velocity Interferometer System for Any Reflection) probe during the dynamic loading. Our result reveals that, under a better test condition with no rarefaction disturbing from the window (present in previous experiments), an elastic-plastic response does exist in the process of reloading from an initial shock state (24 GPa). This validates that the quasi-elastic response of metals under recompression, which had been reported by Asay et al, is an intrinsic character of the materials. Some discussion about the experimental technique for measuring the constitutive parameters of metals at high pressures will be presented also.

Research on Using Raman Spectra of Carborundum Anvil as Pressure Sensor at Pressure of 0.1~3 000 MPa

QU Qing-Ming, ZHENG Hai-Fei

2007, 21(3): 332-336 . doi: 10.11858/gywlxb.2007.03.020

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Abstract:
The 6H carborundum anvil is used in the Mao-Bell hydrothermal diamond anvil cell, and the Raman spectra of different positions of the surface of the anvil under different pressures were measured. The pressures were calculated by using the R1 line of the ruby which was positioned in the cell. Then we discuss on the feasibility of using the 969 cm-1 Raman peak of the carborundum anvil for pressure measurement in certain conditions and the advantages and disadvantages of doing so. After that, we found the following formula for calculating pressures under room temperature, which can be used if one does not change the measurement point of the carborundum anvil.

2007 Vol. 21, No. 3

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