Vol. 29, No. 4 (1980)
1980-02-20
CONTENT
1980, 29 (4): 409-418.
doi: 10.7498/aps.29.409
Abstract +
By using numerical method, the superconducting critical temperature Tc is cal-culated from the Eliashberg equation and the dependence of Tc on λ and the shape of effective phonon spectrum is investigated. In this study, α2F(ω) is taken as the double delta-function spectrum and the spectrum parameters are permited to change over a wide range. It is found with surprising that in the regime of λc series solution, Tc depends, not only on λ and ratios of moments but also on Λ, the reciprocal of the convergence radius of the Tc series solution, and the relation between them shows a certain regularity. Under the light of these results, an approximate Tc formula for the case of μ*= 0 is constructed in the regime of λ 0, or Λ is greater than λ0 but λ is smaller than λ0. Here, λ0 is a parameter depending on the shape of spectrum and its definition is given in this paper. For other type A.superconductors (λ0c is determined is not λ, but δ=1/∧0.5(ω1/2/ωlog)5.5λ1.55.
1980, 29 (4): 419-428.
doi: 10.7498/aps.29.419
Abstract +
We propose here a simple theoretical method to calculate excitation cross sections for electron-ion collision processes. At low energies, we apply the Multichannel Quantum Defect Theory to calculate excitation cross sections based on accurate data of energy levels which have been deduced from extensive spectroscopic measurements. At high energies, we then calculate cross sections based on Bethe Theory. At intermediate energies, we can apply interpolations to calculate mean cross sections if we smooth out local resonance structures. Reliable data for electronic impact excitations of ions are useful in the controlled thermalnuclear reaction researches. As an example, we calculate the (2S-2P) excitation for lithium-like ions to illustrate our proposed theoretical method.
1980, 29 (4): 429-438.
doi: 10.7498/aps.29.429
Abstract +
It is shown that a laser by using the relativistic Doppler effects of high energy ion beam in negative temperature state will be continuously turnable from infrared to X-ray region. The turnability range is △νT=2ν0βγ. The relativistic fransform of the laser parameters are given, and the gain, threshold" and output parameters of the relativistic ion beam laser are calculated in the present work. The methods to excite ion beam by means of laser are analysed. The design of He+ and Ar+ ion beam lasers are also discussed.
1980, 29 (4): 439-446.
doi: 10.7498/aps.29.439
Abstract +
This paper describes the outline, the technical details and the output beam characteristics of a six-beam high-power Nd glass laser system used to irradiate [(CD2)n] spherical targets. The laser pulse width can be varied from 1 ns to 4 ns. If the pulse length is 2ns, the output energy of each of the six-beams is approximately 50 J, the beam divergence being 0.4 mrad and the total output power of all these beams approaching approximately 1.5 × 1011 watts.
1980, 29 (4): 447-453.
doi: 10.7498/aps.29.447
Abstract +
In the direct method of crystal structure determination, one usually applies the symbolic addition method and multiple tangent-formula method. For determination of the phase, the selection of starting reflexion set is a key problem for successful analysis of the crystal structures. The convergence method has been applied for determination of starting reflexion set. This paper presents an optimal selection method on starting reflexion set on the basis of the relations between the diffraction indexes and gives an example of examining a known structure.
1980, 29 (4): 454-460.
doi: 10.7498/aps.29.454
Abstract +
A detailed experimental investigation of the current relaxation of α-LiIO3 single crystals is reported in this article. It was found that after turn off of the dc field initially applied in the direction of C-axis, the decrease of current follows a negative power law (t/t0)-α from the beginning responding time of our apparatus to a certain time tk, and after tk the current decreases approximately as (t/t0)(-α′ln(t/t0)). The parameters α,α′ and tk depend on the temperature of the specimen and the magnitude of the applied field.Nearly ten specimens were measured, with a small dc field the results obtained on most crystals show that the parameters α and α′ change from specimen to specimen but have their values within the following range:0.43≤α≤0.7, 0.07≤α′≤ 0.09. We also found that both the relaxation behavior of the apparent dielectric constant and that of neutron diffraction observed on α-LiIO3 conform to the same empirical expression as given above for the depolarization current except with different parameters. It may be concluded that these relaxation processes would be due to the same physical origin.
1980, 29 (4): 461-468.
doi: 10.7498/aps.29.461
Abstract +
This paper describes the results of X-ray study of imperfection in the single crystal of large area synthetic fluorophlogopite. By using X-ray Laue method, it is showed that in synthetic mica there is a greater degree of one-dimensional disorder, and therefore there are a number of disarranged regions of stacking sequence and their boundaries. The X-ray diffraction topography method shows that most of sub-grain boundaries and dislocations originate from the seed and run normal to the growth surfaces. The density of crystal defects in the region near the crystal surface is greater than that in the center. The difference in the distribution of defects between synthetic mica and natural mica was investigated. The relationships between defects in synthetic mica plate and their performances as used to construct condenser were also studied and discussed.
1980, 29 (4): 469-484.
doi: 10.7498/aps.29.469
Abstract +
Debye-Scherrer photographs have been taken from forty-four slowly cooled and quenched manganese-gallium alloys. These, incorporated with the differential thermal analysis taken at the gallium-rich side, provide a basis for the Mn-Ga constitutional diagram.There are ten different phases beside pure Ga in the entire system. The solid solubility of Mn in Ga is almost undetectable. The α phase is the primary solid solution of Ga in α-Mn. The solubility limit at room temperature is 1.95 at % Ga. The β phase has a homogeneity range from 8.6 to 19.2 at % Ga at room temperature. The structure is that of β-Mn. It may be looked upon as a solid solution of Ga in β-Mn, stabilized at room temperature due to the random substitution of some of the Mn atoms by Ga. The γ phase may be divided into three parts, γ1, γ2, and γ3. γ1 is face-centred cubic, γ2, face-centred tetragonal, while γ3, face-centred tetragonal with a long range order. The structure of γ3 is isomorphous with CuAu I in the Cu-Au system. γ3 is stable at room temperature, the homogeneity range being from 37 to 45 at% Ga; while γ1 is only stable at high temperatures. The transformations from γ1 to γ2 and then to γ3 are of the second degree, the degree of order increasing with the Ga content and decreasing with the temperature. The whole phase γ may be considered as a solid solution of Ga in γ-Mn, which could not be retained by quenching in the pure state. The δ phase exists only at high temperatures. It may be regarded as a solid solution of Ga in δ-Mn, deformed and ordered by the substitution of some of the Mn atoms by Ga. The ε phase has an ordered hexagonal close-packed structure with eight atoms per unit cell. It is formed congruently from the y phase at about 820℃. The homogeneity range at room temperature is estimated to be from 27 to 30 at% Ga. The η phase has a wide range at room temperature, estimated to be from 50 to 60 at% Ga. From 520 to 600℃, it undergoes a polymorphic transformation to another phase λ, the homogeneity range of which being displaced with temperature toward the Mn-rich side. Both η and λ indicate quite complicated structures. At the Ga-rich side, there are three intermediate phases x, φ and ω. They are formed by peritectoid or peritectic reactions. The ideal structure of φ is cubic of the NiHg4 type, but it lies outside of the very narrow homogeneity range around Mn2.3 Gay7.7. Most probably the stoichiometric composition of the ω phase is Mn2Ga9 or MnGa5. Among the six intermediate phases stable at room temperature, β, ε, γ3, x and φ are ferromagnetic. The most pronounced ferromagnetic alloys have been found in the γ3 and φ regions which are rich in Ga content. Saturation magnetizations and Curie points for some of the alloys have been determined.
1980, 29 (4): 485-493.
doi: 10.7498/aps.29.485
Abstract +
In general, the quantitative electron probe microanalysis is based on comparisons with standard samples. In this article, a method of the quantitative analysis of binary alloys without reference to standard samples is introduced. After simultaneous measurements of the ratios of the Ka photons of two elements in the binary alloys (Cu-Ga, GaAs) in SEM-EDS equipment, the constituents of the binary alloys are calculated from a simplified formula for the energy loss of the incident electrons, the X-ray excitation cross-section and the secondary fluorescence. When the overvol-tage of the incident electrons is kept in the range 2-3, the calculated results show good agreement with the actual constituents. The "instrument sensitivity" of the characteristic X-ray of the pure elements determined in the literature is calculated and discussed by using this simplified model.
1980, 29 (4): 494-499.
doi: 10.7498/aps.29.494
Abstract +
The partial dislocations bordering a stacking fault and appearing on a coherent twin boundary in a Ni-Cr alloy (20% Cr, 1% Al, 2.5% Ti) were studied by TEM and the findings are as follows:1. The using of g·bp=±2/3 or ±1/3 as the criterion of appearance or disappearance of partial dislocations is acceptable, though not rigorous. Therefore, it is preferrable to choose {220} or {311} reflections to form diffraction contrast image and use g·bp = 0 to determine the Burgers vectors of the partial dislocations.2. Partial dislocation pairs appeared on coherent twin boundaries as a consequence of the dissociation of perfect dislocations.3. Stacking faults on parallel slip planes move and sometimes overlap each other. In overlapping faults the partial dislocations separating intrinsic and extrinsic faults showed no contrast when g·bp = ± 2/3 and appeared as white lines on the dark background of stacking faults, while they appeared as dark lines when g·bp= ± 1/3.
BRIEF REPORT
1980, 29 (4): 500-507.
doi: 10.7498/aps.29.500
Abstract +
Experimental observations of the high energy pulsed CO2 Laser-target interaction were made by high-speed interference photography and high-speed shadowgra-phy to reveal various effects in front of the surface as well as the reflection and diffraction of a shock wave. Brief analyses are presented.
1980, 29 (4): 508-510.
doi: 10.7498/aps.29.508
Abstract +
In this paper, degenerate four-wave mixing was studied in various transparent optical media. Third-order susceptibility has been determined by the ratio of the input probing beam in tensity to the backward wave intensity in four-wave mixing. The results of some solvents and glass media are presented.
1980, 29 (4): 511-516.
doi: 10.7498/aps.29.511
Abstract +
Near the N→SA transition point, recent observations show that the anomalous increase in the volume viscosity is much greater than that of the shear viscosity. This is explained in terms of the time correlation function for viscosity. The reason for the disagreement between the experimental results and the Brochard's theory is also given.
1980, 29 (4): 517-523.
doi: 10.7498/aps.29.517
Abstract +
The properties of a Prankel exeiton in a polar crystal is discussed by means of a model which takes account of the atomicity of the lattice. The lattice vibration and the interaction of the exeiton with the lattice displacement is discussed by second quantization method. The temperature dependence of the effective mass of Frankel exeiton is derived.
1980, 29 (4): 524-528.
doi: 10.7498/aps.29.524
Abstract +
After bombarding the Ni(001) surface by an Ar ion beam with primary energy of 500 eV and beam current of 5 μA in the presence of residual nitrogen under a total pressure of 5×10-5 torr, we have found a P(2×2) structure formed by the adsorption of nitrogen on Ni(001) surface by means of LBED. This is much similar to the structure caused by the adsorption of oxygen or the segregation of carbon with a surface concentration of one quarter monolayer on the same crystal surface. A primary discussion on the nature of nickel-nitrogen bond has been made.
1980, 29 (4): 529-532.
doi: 10.7498/aps.29.529
Abstract +
Argon ion sputtering alone does not remove completely the carbon remained on the nickel surface. By bombarding the nickel surface contaminated with carbon with an electron beam under a pressure of 10-8-10-9 torr to enhance the adsorption of oxygen on it, we obtain a nickel surface with both absorbed oxygen and carbon. Heating this surface at 360℃ for 45 minutes, we could obtain an atomically clean surface without carbon. The conditions and the possible machanism of removing residual carbon by oxygen are disccused.
