高压物理学报

A Study on the Compression Law of H- Ions in the Alkali Hydride Crystals by the Ionic Overlap-Compression Model

WANG Xin-Qiang, GOU Qing-Quan

1993, 7(3): 161-166 . doi: 10.11858/gywlxb.1993.03.001

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Abstract:
By using the ionic overlap-compression model, the parameter describing the state of H- by ions in the alkali hydride crystals (LiH, NaH and KH) was calculated by variation method. Then the numerical relations of and the relative radius of H- ions with the pressure were determined. The results show that the compression of H- ions has occurred before the pressure is added, and the compression law almost has nothing to do with the crystal structures. These two points are physically reasonable and were confirmed indirectly by the experiments.

Pressure-Induced Non-crystallization in Eu2+ Activated Sr-Borates

LIU Wei-Na, LIU Hong-Jian, FENG Yu-Chen, SUN Shu-Lan, SU Wen-Hui

1993, 7(3): 167-176 . doi: 10.11858/gywlxb.1993.03.002

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Abstract:
High pressure-induced crystallization in disordered or non-crystalline matter is well known. Pressure-induced disordering or non-crystallizing in crystals, however, has been seldom found so far. In the present paper, under the pressure of 3.0~7.0 GPa, the pressure-induced non-crystallization phenomena in Eu2+ activated orthorhombic Sr-borates crystals were investigated by using X-ray diffraction, emission and excitation spectra of Eu2+, Raman spectra and SEM topography. After treating at 3.0 GPa, the X-ray diffraction spectra of the sample exhibit a new character in which a set of clearly widened peaks of the crystal were superposed on the diffuse peaks of non-crystalline state; the intensity of the emission spectrum peaking at 370 nm, which is given by 5d4f transition of Eu2+ located in orthorhombic crystal, decreased and widened obviously, and a broad band of emission spectrum peaking at 440 nm, which is given by Eu2+ located in non-crystalline state, was also observed; the excitation spectra for the two emission bands differed with each other considerably; the intensity of Raman peaks decreased and their half width increased; the particle size observed by SEM remained in the order of micrometer of orthorhombic crystal grain synthesized under normal pressure. As the pressure increasing, the width of X-ray diffraction peaks for the crystalline state increased, but the total diffraction intensity further decreased, shile the total intensity of diffuse peaks for the non-crystalline state further increased; the emission band peaking at 370 nm was not observed, only a very low emission peak was recorded at 440 nm; Raman peaks were further decreased and widened, too; the particle size observed by SEM did not vary apparently. Analyses from the experimental results of X-ray diffraction show the pressure effects in the fining of crystal grains, the non-crystallization of crystalline state, and the grain size reduction from the order of micrometer to nanometer. They are 2 m (0.1 MPa), 49.4 nm (3.0 GPa), 29.7 nm (5.0 GPa), 25.1 nm (7.0 GPa), respectively. The volume ratio fo crystalline to non-crystalline state with increasing pressure was found, they are 70/30 (3.0 GPa), 63/37 (5.0 GPa), 57/43 (7.0 GPa), respectively. The symmetry of crystal field around Eu2+ in crystalline and non-crystalline state formed under the high pressure is different and lowering. The lowering and widening of Raman peaks result from pressure-induced fining of grain to nanometer in size. Combining the results about the grain size of SEM and X-ray diffraction, it seems that the pressure-induced nano-grains exhibits in the form that there exist sub-grains in the larger grains of micrometer. The interface zone between the sub-grain is probably in non-crystalline state.

X-Ray Observations of the Shock-Induced Transformation from gBN to wBN

TAN Hua, HAN Jun Wan, WANG Long-Shu, HE Jia-Qing

1993, 7(3): 177-182 . doi: 10.11858/gywlxb.1993.03.003

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Abstract:
X-ray diffraction observations were used to analyze the phase transformation of graphite-type BN (gBN) with different crystallinities to wurtzit-type BN (wBN) under the same shock compression conditions. Impurities contained in the wBN powders were also estimated. Results show that the conversion ratio from gBN to wBN are greatly affected by the graphite index number (G.I) of the raw materials.

Study on Wurtzite Type Boron Nitride and Its Applications (Ⅱ)Isothermal Equation of State for Wurtzite Type Boron Nitride

LIU Bing-Bing, YANG Hai-Bin, CHI Yuan-Bin, LI Ming-Hui, WANG Li-Zhong

1993, 7(3): 183-190 . doi: 10.11858/gywlxb.1993.03.004

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Abstract:
In our experiments, the isothermal equation of state of wBN is studied by two different in situ high pressure X-ray diffraction methods at room temperature. The sample is obtained by shock compression. One of the methods is the rotating anode X-ray angle dispersive powder diffraction by which wBN is studied up to 40 GPa. The results indicated that wBN is structurally stable below 40 GPa and no phase transition is observed. The Murnaghan isothermal equation of state for the sample is fitted with the bulk modulus at zero pressure, B0=(33534) GPa, and its pressure deviation B0'=4.21. The other method is the synchrotron radiation X-ray energy dispersive diffraction (EDXD) by which the isothermal equation is studied with improved MaoBell type diamond anvil cell up to 25 GPa. The loading mechanism of the improved DAC is stepping and automatic, which maintains the fixed scattering angle. The Murnaghan isothermal equation is also fitted with the bulk modulus at zero pressure, B0=(28056) GPa, and its pressure deviation B0'=4.39.

Magnetization Character of Amorphous Magnetic Alloys at High Hydrostatic Pressure

SU Fang, HUANG Ding

1993, 7(3): 191-201 . doi: 10.11858/gywlxb.1993.03.005

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Abstract:
Magnetization curves and magnetic permeability of amorphous alloys FeCoNiSiVB, FeSiB, FeCrSiB, FeCoSiB in the hydrostatic pressure range of 0.000 1~2.4 GPa were investigated. Besides, the relation between pressure and the maximum magnetic permeability max of the four alloys was obtained with accurate fitting of the polynomial and comparing of computer one by one. It is found that (1) for intensity of magnetic induction Bs the general trend is to decrease with the increase of pressure; (2) in 2~3 pressure range, Bs presents a anomalous rise. In our discussion, (1) is due to the fact that exchange-integral constant A drops with the reduction of atomic interval, which causes the intensity of spontaneous magnetization to descend in magnetic domain; (2) probably comes from some changes of chemical short range order in microscopic structures of amorphous alloys at high pressure.

X-Ray Diffraction Studies on C60 under High Pressure

LIU Li-Jun, CHEN Liang-Chen, Chen Hong, WANG Ru-Ju, ZHANG Zhi-Ting, CHE Rong-Zheng, ZHOU Lei, WANG Ji-Fang, LI Yu-Liang, YAO You-Xin, et al

1993, 7(3): 202-207 . doi: 10.11858/gywlxb.1993.03.006

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Abstract:
In situ high pressure X-ray diffraction experiments have been done for super-pure C60 powder sample using synchrotron radiation X-ray source and an energy dispersion detector. The pressure is generated by DAC. Pt was used as an inner pressure standard, whose EOS is known. The pressure of the sample was determined by the diffraction data of Pt. The maximum experimental pressure is 30 GPa. The results indicate that crystal C60 has a fcc structure with lattice parameter a=1.420 86 nm at ambient condition; and the crystal structure of C60 was changed under high pressure. A lower symmetry phase reached at 13.7 GPa, marked by the splitting of broaden continuously and their intensities became very week. The background raised obviously at about 25 GPa, it showed that C60 crystal began to transform to an amorphous state. The diffraction lines disappeared wholly, thus the transformation to amorphous state was finished completely at about 30 GPa. We also carried out X-ray diffraction experiments for C60 samples quenched at various pressure up to 44 GPa. The samples were in non-hydrostatic pressures. The spectra showed that crystal C60 transformed to amorphous state beyond 30 GPa. Finally, the phenomena of pressure-induced transition from crystal to amorphous state are discussed.

A Study on New Orthorhombic Approximants of the Al70Co15Tb5Ni10 Decagonal Quasi-crystal

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

1993, 7(3): 208-213 . doi: 10.11858/gywlxb.1993.03.007

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Abstract:
Two new orthorhombic approximants with the largest until cell observed up to now were found in the Al70Co15Tb5Ni10 decagonal quasi-crystal, which were prepared by quenching (102 ℃/s) the melt state (1 700 ℃) under high static pressure (7.0 GPa). The lattice parameters of the orthorhombic approximant are the same (a=6.1 nm, b=0.4 nm, c=8.4 nm), but the structure of the first phase is P-type and that of the second phase is a B-type. Their structures and lattice parameters are in accordance with that of the present theoretical predictions.

The Principle of the Explosive Welding for Multilayer Amorphous Foils

LI Xiao-Jie, ZHANG Kai

1993, 7(3): 214-219 . doi: 10.11858/gywlxb.1993.03.008

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Abstract:
A dynamic model about the explosive welding of multilayer foils was given in this paper. We proved that the particle velocity behind the shock wave was the impact velocity between the two foils and the dynamic behavior of the multilayer foils system was similar to that of the porous material system. Otherwise, a heat-conduction model was used to explain the heat conduction in the explosive welding of multilayer amorphous ribbons. With above theories a welding window of Fe78B13Si9 amorphous alloy was also given which is in good agreement with its explosive welding results.

Determination of the Vertical Sections of the High Pressure Phase Diagrams of Cd(0.2)-Sn-Zn Ternary Alloy System

SONG Li-Zhu, YANG Hua, ZHAO Mu-Yu, SHEN Zhong-Yi, LIU Yong

1993, 7(3): 220-225 . doi: 10.11858/gywlxb.1993.03.009

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Abstract:
Several vertical sections of the phase diagrams of Cd-Sn-Zn ternary alloy system with a constant composition of xCd=0.2 were determined by differential thermal analysis (DTA) at high pressures. Working pressures were 0, 0.5, 1.0, and 1.5 GPa. The eutectic temperature of the system increased by about 35 K as the pressure going from atmospheric to 1.5 GPa, though the eutectoid composition changed little with pressure in the experiment. This tendency in temperature shifting coincides with the results of calculated phase diagrams. Experimental liquids at 1.5 GPa tallies well with that of calculated results.

A Study of the Equation of State of Alumina Ceramics

LI Da-Hong, WANG Wu

1993, 7(3): 226-231 . doi: 10.11858/gywlxb.1993.03.010

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Abstract:
Equation of state of alumina ceramics was obtained by using explosive loading techniques and impedance match method. The experimentally measured shock velocity D and particle velocity u of this ceramics can be fitted linearly in the form of D==(2.600.20)+(1.650.09)u (km/s). Based on the above experimental results, the Born-Myler potential was used to obtain the Grneisen equation of state of the ceramics.

Calculations of the High Pressure Phase Transition Point of NaCl, KCl and NaF Crystals

ZHANG Cheng-Xiang, WU Shao-Zeng, WU Shu-Yan, WU Xue-Yuan

1993, 7(3): 232-237 . doi: 10.11858/gywlxb.1993.03.011

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Abstract:
By using the theory of lattice dynamics, the Gibbs free energies of NaCl, KCl and NaF crystals were calculated for both NaCl and CsCl structures. Results show that the large, attractive short-range interaction between the second neigbour ions may play an important role in the explanation of the relative stability of NaCl and CsCl structures. By using the potentials obtained from Gordon-Kim model, the pressure of phase transition and the lattice constants were calculated. Results are satisfactory. The effect of temperature on the phase transition point is also investigated. The result shows that the shift in the transition point is very small when temperature changes.

Study on the Heating Technology of Non-constant Power

HAO Zhao-Yin, CHEN Yu-Fei

1993, 7(3): 238-240 . doi: 10.11858/gywlxb.1993.03.012

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Abstract:
In this paper, we have discussed the theory and experimental evidence on the non-constant power heating technology growing diamond at high pressure and temperature and have used this technology for growing good quality diamond crystals.

1993 Vol. 7, No. 3

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