高压物理学报

Breakdown of Ferroelectric Ceramics under Shock Loading

ZHANG Guan-Ren

1995, 9(1): 1-4 . doi: 10.11858/gywlxb.1995.01.001

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Abstract:
By considering the conducting crack as the result of electrical break down, this paper derives a storage energy formula when there is a crack in contact with and perpendicular to a surface of the ferroelectric block. Then the driving energy per unit area of the crack developing surface is deduced. When this energy is greater than the surface energy of the ferroelectric ceramic, the process of breakdown could be developed. From this condition, the critical voltage or shockwave velocity can be derived. Lastly, the results of this paper and others are compared as well.

Conversion Behavior of Various Hexagonal Boron Nitrides to Cubic Boron Nitride

ZHOU Yan-Ping, YAN Xue-Wei, DU Sen-Lin, MA Xian-Feng, CUI Shuo-Jing, ZHAO Wei

1995, 9(1): 5-12 . doi: 10.11858/gywlxb.1995.01.002

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Abstract:
Cubic boron nitride (cBN) is synthesized from seven kinds of the hexagonal boronnitride (hBN) under a pressure of 4.6 GPa and a temperature of 1 600 ℃ with catalyst by using a cubic anvil press. The contrast to the standard curve is made in the present work, and the conversion yields of different kinds of hBN to cBN are measured by powder X-ray diffraction. The relative degree of three-dimensional order of various hBN raw materials is determined. Graphitization index (G.I value), crystalline grain size, and unit cell constants are calculated on data of XRD, and their effects on the conversion yields of hBN to cBN investigated. The hBN with better crystallinity and smaller crystalline grain size shows higher conversion rate to cBN. On the phase transformation from hBN to cBN, we suggest a direct conversion with two-dimensional nucleation as a possible mechanism. The theoretical description based on the homogeneous nucleation mechanism yields reasonable results according to experimental data.

Approximants C4 and C5 of the Decagonal Quasicrystal in Al70Co15Ni10Tb5 Alloy Obtained by Quenching from Melting State under High Static Pressure

YU Ri-Cheng, XU Da-Peng, SU Wen-Hui, PANG Xin-Yan

1995, 9(1): 13-19 . doi: 10.11858/gywlxb.1995.01.003

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Abstract:
Two new approximants of the decagonal quasicrystal were found in the Al70Co15Ni10Tb5 alloy, which was prepared by quenching from melting state under high static pressure (7.0 GPa). The lattice parameters of the approximants were =1.38 nm, b=1.6 nm, c=2.0 nm (C4, B-type orthorhombic crystalline phase); =1.20 nm, b=1.60 nm, c= 2.30 nm (C5, P-type orthorhombic crystalline phase), respectively. They were also studied by means of high-resolution electron microscopy (HREM). It was found that there was a close relationship between them. The HREM pattern can be regarded as an ordered one of Penrose tiling.

Experimental Studies of the Thermal Shock Wave Produced in the Flat Plate Targets Bombarded by Electron Beam on 'Flash-Ⅱ'

PENG Chang-Xian, WANG Zhan-Jiang, WANG Wei, WANG Zheng, XU Yong-Liang, CHENG Gui-Gan

1995, 9(1): 20-28 . doi: 10.11858/gywlxb.1995.01.004

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Abstract:
The thermal shock wave is an important mechanic phenomenon of the material response produced in the target material bombarded by electron beam. In this paper, the experimental studies of the thermal shock wave produced in the flat plate targets bombarded by electron beam on FLASH Ⅱ equipment during the recent years are discussed. The target material is LY-12 aluminum alloy with thicknesses of 2.8～6.5 mm. The range of energy fluxes on targets is 87～152 J/cm2. Experimentally measured stress peaks of the thermal shock waves is 0.35～2.0 GPa, average acting time of the thermal shock waves about 0.29 s, average semi-high width about 0.14 s, and average rise time about 0.10 s.

Synthesis of T1-System Monophase Superconductors under Oxygen Pressure and Its High Pressure Effect

LIU Zhen-Xing, MENG Xian-Ren, SHEN De-Yuan, LIN Ming-Zhu, TU Qing-Yun, LIN Zhen-Jin, SANG Li-Hua, PENG Zhi-Qiang

1995, 9(1): 29-33 . doi: 10.11858/gywlxb.1995.01.005

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Abstract:
Effect of oxygen pressure on the preparation of TI-system superconductors at pressure 0～3 MPa is reported. Under the same sintering temperature and in the same duration, the phase fractions and Tc as well as the weight loss are found to depend directly on the oxygen pressure. When the oxygen pressure is higher than 1.45 MPa, we can get pure 2212 phase super conductors. The samples contain both 2212 and 2223 phase if the oxygen pressure is 0.9～1.45 MPa. Pure 2223 phase samples can be obtained when the oxygen pressure is 0.25～0.9 MPa. The high pressure effect on samples with 2223 phase and 2212 phase also was studied. The dTc0/dp for sample with 2223 phase is 4 K/GPa, and 2 K/GPa for sample with 2212 phase under pressure 0～0.52 GPa. The sample with 2223 phase has stronger pressure effect than their sample with 2212 phase.

Effect of Structure Inhomogeneity of the Surface Lattice on Diamond Morphology

ZHANG Shu-Da, ZHU Yao-Hua

1995, 9(1): 34-38 . doi: 10.11858/gywlxb.1995.01.006

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Abstract:
According to W. D. Harkins' theory we calculated the surface energy of some diamond planes as: (100)=9.068 J/m2, (110)=6.412 J/m2, (111)=15.706 J/m2 and b(111)=5.235 J/m2. If the final form of diamond could be accounted for by Gibbe-Wulff's crystal growth taw, the probability of the appearance of {110} planes in the final form of diamond would be much large than that of the {100} planes. But this is in contrast to the actual fact. In this paper we introduce both the sarface energy and the surface structure inhomogeneity free enthalpy Gsti to interpret, from the thermodynamics analyses, why the {110} planes often disappear as the diamond crystal grows. Some related data were calculated by converse inference method.

Microstructure and Pressure Dependence of Resistivity in Alloy FeCuNbMSiB (M＝Nb, V, Mo) with Nanophase Crystallization

SU Fang, XIE-Bin

1995, 9(1): 39-48 . doi: 10.11858/gywlxb.1995.01.007

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Abstract:
The results on X-ray diffraction and transmission electron microscope indicated that crystallized nanophase was -Fe(Si) solid solution in amorphous FeCuNbMSiB (M=Nb, V, Mo) alloys after annealing at 540 ℃ for 20 min. Graininess of -Fe(Si) was 10～20 nm. Besides, their resistivity under atmospheric pressure and room temperature and variation of resistivity with hydrostatic pressure were measured in detail in the range from 0.000 1 to 2.40 GPa. Linear empirical equations of their relative resistivity to pressure were obtained by fitting on computer. Finally, effect of annealing mode and temperature on forming nanophase crystallization were discussed.

Effects of the Cluster Model for Diamond (111) Plane on the Interactive Potential between Methyl and the Surface

LIU Bo, QIAN Xing-Zhong, DAI Zhen-Wen, PAN Shou-Fu

1995, 9(1): 49-52 . doi: 10.11858/gywlxb.1995.01.008

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Abstract:
The effects of the cluster model for diamond (111) plane on the interactive potential between methyl and the surface were investigated theoretically and computationally. We concluded that a small cluster model with fewer layers is nearly as reasonable as a larger one with more layers, the error in reactive energy is about 20 kJ/mol. A rule to find out more reasonable cluster model was also given.

Morphology and Thermal Stability of Shock Synthesized wBN Powders

TAN Hua, HAN Jun-Wan, HE Hong-Liang, WANG Xiao-Jiang

1995, 9(1): 53-58 . doi: 10.11858/gywlxb.1995.01.009

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Abstract:
We reported some main features of shock synthesized wBN ceramic powders by its morphology, specific surface area, microdensity, crystallite size as well as the B to N atomic ratio. These will reflect, from anoth side, the unique high defect density which exists in the wBN crystals. We also analyzed the observed behavior of wBN powders under ambient pressure and high temperature (up to 1 500 ℃) by TG and DTA observation in air, N2 and Ar gas.

Numerical Simulation of the Radiance in Shock Temperature Measurement

LIN Hua-Ling, YU Wan-Rui

1995, 9(1): 59-68 . doi: 10.11858/gywlxb.1995.01.010

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Abstract:
Considering the effects of the window opacity, the interface emissivity and the heat conduction on the radiance in shock temperature measurements, we present that the increase of opacity under shock compression is an important factor that influences the time dependence of the radiance. Using the equation of hydrodynamics, the equation of radiation transport and the heat conduction, we numerically simulate the radiance, which agrees with the experimental result.

A Pressure-Induced Phase Transition Study of -BaB2O4 Crystal by X-Ray Diffraction

GU Hui-Cheng, CHEN Liang-Chen, LI Feng-Ying, CHE Rong-Zheng, CHEN Hong, WANG Ji-Fang, LIN Yuan-Kun, LAN Guo-Xiang

1995, 9(1): 69-73 . doi: 10.11858/gywlxb.1995.01.011

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Abstract:
Phase transitions of -BaB2O4 crystal have been studied by using X-ray powder diffraction technique with a diamond anvil cell (DAC) at high pressure up to 17.6 GPa. According to the X-ray diffraction results, -BaB2O4 crystal undergoes three pressure-induced phase transitions neat 2.2 GPa, 5.3 GPa, 11.5 GPa, respectively. The phase transitions are reversible below 11.5 GPa. -BaB2O4 becomes amorphous and the phase transition is irreversible above 11.5 GPa.

Study of Intermediate Layers between Diamond Film and Non-Diamond Substrates

YANG Guo-Wei, MAO You-De

1995, 9(1): 74-80 . doi: 10.11858/gywlxb.1995.01.012

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Abstract:
The intermediate layers between diamond films and non-diamond substrates. in diamond film system grown with low pressure vapor phase methods, have been studied by interface energy theory. We have put forward the theoretical mechanism of the existence of intermediate layers, and explained some experiment results of intermediate layers.

1995 Vol. 9, No. 1

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