高压物理学报

Structural Characters and the Conductivity of Nd2-xCexCuO4 Samples prepared under Atmosphere and High Pressure

LIU Hong-Jian, LI Li-Ping, WANG Yi-Feng, SU Wen-Hui

1991, 5(3): 161-168 . doi: 10.11858/gywlxb.1991.03.001

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Abstract:
Samples of Nd2-xCexCuO4 have been synthesized by using atmosphere pressure-high temperature (AT) and high pressure-high temperature (HP) methods. The structural characters and electrical conductivity of the samples prepared by the two different methods have been studied. The sample synthesized by HP (1.7 GPa, 800 ℃, 10 min) has a tetragonal structure (T' phase), similar to that of the samples sintered by AP (1 000 ℃, 10 h), but their crystal parameter, c, varies in a different manner as the Ce4+ doping content, x, changes. The parameter c for HP products remains basically constant as the doping content x increases, whereas the parameter c for the AP products decreases obviously as x increases. Both samples prepared by AP and HP methods exhibit semiconducting properties in varying degrees under liquid nitrogen temperatures. The electrical conductivity of the HP samples, quenched at high temperature, is superior to that of AP samples. Experiments show that high pressure is beneficial to reduce the synthesis temperature, to shorten the reactive time of solid state reaction and, particularly, to improve the electrical conductivity of the samples due to the reduction role of high pressure.

Isothermal Compression and High Pressure Phase Transformation of Nickel Oxide (Bunsenite)

XIONG Da-He

1991, 5(3): 169-176 . doi: 10.11858/gywlxb.1991.03.002

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Abstract:
Nickel oxide (NiO, Bunsenite) has been used as an analogue modeling composition in relation to other monoxide as MgO, FeO of earth interior. Crystal structure change of NiO from NaCl type fcc to rhombohedral was discovered by Rooksby in 1943 at low temperature183 ℃. We recently carried out experiments under high pressure to 12.0 GPa using diamond anvil cell with liquid pressure transmitting medium and direct compression to 29 GPa. Our experimental results show the isothermal compression of NiO under pressure from 1.22 GPa to 8.87 GPa, lattice parameters and molal volume. At zero pressure: a0=0.418 24 nm; Vm=11.009 910-3 nm3; density, 6.780 2 g/cm3 and at 8.87 GPa; a=0.411 39 nm; Vm=10.481 910-3 nm3; density, 7.125 4 g/cm3. All data show a small deviation from Drickamer and S. K. Agrawals results. The diffraction lines (111), (220) of NiO suddenly splitting until pressure loading up to 12 GPa at hydrostatic compression. Phase change of NiO from cubic to rhombohedral. The same results obtained by direct compression at pressure to 5.8 GPa and up to 29 GPa. Lattice parameter of rhomb, new phase a=0.296 70 nm; c=0.700 00 nm; Vm=10.708 410-3 nm3; density, 6.972 6 g/cm3, this date agree with Rooksby's a=0.296 60 nm. The magnetic properties of NiO vary with pressure change Neel temperature of NiO 250 ℃ (523 K), decreases, when pressure increases, whereas below Neel temperature NiO changed in antiferromagnetic and rhombohedral crystal structure. Calculation bulk modulus of NiO by Birch-Manghnahan equation best fits to the p-V data and assuming K0' values of 4, give K0=166.83 GPa. Molal volume vs bulk modulus shows the compressibility of NiO is approaching to MgO.

Fe-Based Alloys and the Growth of Single Crystal Diamond

HAO Zhao-Yin, WANG Kui-Xiang

1991, 5(3): 177-181 . doi: 10.11858/gywlxb.1991.03.003

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Abstract:
In this paper, we revealed the relationship between the magnetic properties of Fe-based catalysts at ambient conditions and the growth of single crystal diamond, by comparing the different results obtained in the growth of single crystal diamond with the lattice constant, component, magnetic moment and Mossbauer spectra of the catalysts.

Effects of High Pressures on Bi2+xSr2Ca1-xCu2Oy Superconducting Single Crystals with Different Tc

LIU Zhen-Xing, HAO Xiu-Yu, LI Jian-Qi, XIONG Ji-Wu, JIA Shun-Lian, ZHAO Zhong-Xian

1991, 5(3): 182-185 . doi: 10.11858/gywlxb.1991.03.004

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Abstract:
Under high pressures the Tc of Bi-Sr-Ca-Cu-O single crystals with different content segregation will change differently. We found that, samples with larger segregation and lower Tc exhibit higher dTc/dp. When the sample approaches to the ideal composition, it exhibit lowest dTc/dp. The high pressure effects on Tc may be closely related to the variation of bonding length.

Calculations of the Isothermal Sections of the Phase Diagram of the Cd-Sn-Zn Ternary System at High Pressure

SONG Li-Zhu, WU Feng-Qing, ZHAO Mu-Yu

1991, 5(3): 186-192 . doi: 10.11858/gywlxb.1991.03.005

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Abstract:
According to the phase boundary theory the principle of the chemical potentials of each component in the different phases being equal in an equilibrium system, the horizontal sections and liquids projections of the phase diagram of Cd-Sn-Zn ternary system at constant temperature 500 K and different high pressures are calculated, and presented in figs. In this system, the form of liquids projection at a constant high pressure of 2.0 GPa is similar to that at normal pressure but the liquid regions of the former become smaller. Due to the effect of high pressure, the ternary eutectic temperature is increased by about 60 K.

Formation of Hexagonal Closed Packed Metas-Table Phase during the Solidification of Ag-20 at% Ge Melt under High Pressure

QIN Zhi-Cheng, WANG Wen-Kui, CHEN Hong

1991, 5(3): 193-196 . doi: 10.11858/gywlxb.1991.03.006

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Abstract:
The metastable hexagonal closed packed phase with lattice parameters a=0.289 8 nm, c=0.470 8 nm and c/a=1.625 has been obtained by melt quenching of Ag-20 at% Ge alloy under high pressure. The application of a pressure of 7.2 GPa to melt quenching induced a decreasing of cooling rate in magnitude of four orders for the formation of the hexagonal phase.

Analysis of the Morphologies of Diamond Film Grown by Microwave Plasma CVD Method

FANG Li-Li, ZHANG Zhan, LI Jia, MA Li-Ying, ZHAO Hao-Min, YU Hong-Chang, WU Bao-Shan

1991, 5(3): 197-204 . doi: 10.11858/gywlxb.1991.03.007

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Abstract:
In this paper, morphologies of polycrystalline diamond film and epitaxial single-crystal diamond film by microwave plasma CVD method were reported, the causes of these morphologies were analyzed.

Velocity Measurement of Magnet Induced System for Projectile

SHI Shang-Chun, CHEN Pan-Sen, HUANG Yue

1991, 5(3): 205-214 . doi: 10.11858/gywlxb.1991.03.008

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Abstract:
A new system, which can measure the projectile velocity accurately, has recently been developed and successfully applied to a two stage light gas gun of 23 mm in launch tube diameter. This system mainly consists of a magnetic induction part, a digital wave memory device and an automatic treatment system by personal computer. Accuracies in time observation and velocity measurement are 0.03% and about 0.10%, respectively, for the projectiles velocity, from 1 to 6 km/s. The high accuracy is due to the adoption of the techniques in compressed magnetic field designation and the over-zero time treatment of signals.

Some Quality Problems of PDC

QI Zeng-Du, ZHOU Jun-Xue, CAO Zhen-Jun, WANG Ming-Zhong

1991, 5(3): 215-219 . doi: 10.11858/gywlxb.1991.03.009

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Abstract:
This paper discusses a few quality problems encountered in the manufacturing of polycrystal diamond composites (PDC), the reasons that causes the problem and the ways to solve them.

Atomic Boundary Potential Correction to Equation of State for Thomas-Fermi Model

LI Zhao-Ning, PAN Shou-Fu

1991, 5(3): 220-226 . doi: 10.11858/gywlxb.1991.03.010

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Abstract:
A simple TFL (Thomas-Fermi-Like) model was proposed, in which a non zero atomic coundary potential was considered. The calculation results for 13Al atom were compared with TFD (Thomas-Fermi-Dirac), TFS (Thomas-Fermi-Shell) and AA (Average-Atom) models.

Relations of Diamond Synthesis with the Synthesizing System

LIN Ming-Xi, RUAN Yong-Cai

1991, 5(3): 227-232 . doi: 10.11858/gywlxb.1991.03.011

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Abstract:
After studying various material behavior in the diamond synthesis processes and by measuring the factors in the HP/HT apparatus, we summarized the characteristics of diamond growth as follows: diamond grows on the graphite (G)-metal catalyst (Me) material interface. Since the resistance R(G)R(Me), temperature T(G)T(Me) and the heat exchange with outside, et al., the pressure and temperature gradients thus created in the cell will become the driving force of diamond growth. Too large or too small a driving force will be harmful to diamond growth. On the surface of each diamond crystal grain, there is a thin metallic layer of thickness about 15~20 m. This metallic thin film can both act as the carbon carrier as well as the catalyst. The growth of a coarse grain of high-strength diamond requires a stable synthesis system. The paper analyzed the property of such a system and proposed a way to establish the system.

The Response of PVF2 on High Velocity Gas-FluidObservations of the Behavior of Diffluence System for a Two Stage Light Gas Gun

SUN Zhu-Mei, HU Dong, SHI Shang-Chun, SHEN Shou-Peng

1991, 5(3): 233-240 . doi: 10.11858/gywlxb.1991.03.012

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Abstract:
A PVF2 (polyvinylidene fluorid) gauge, which is suitable for the measurements of the response of the curved surfaces in small space on high velocity gas fluid is described in this paper. A sensitive trigger system, with which the response of PVF2 to high velocity gas-fluid can be reliably measured, is also developed. The behavior of the diffluence system for a two stage light gas gun has been successfully observed by using this technique. The results show that actions of gas-fluid after diffluence on the target can be reduced rapidly to ten percent, and it will be sufficient for most experimental requirements if three diffluence plates are used.

1991 Vol. 5, No. 3

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