Vol. 32, No. 12 (1983)
1983-06-20
CONTENT
1983, 32 (12): 1479-1488.
doi: 10.7498/aps.32.1479
Abstract +
Fringe images of overlapping micro-twin boundaries in a f.c.c. Ni-Cr alloy have been observed by trausmission electron microscopy. It is shown that the average intensity of the fringe images in the overlapping boundary is either much higher or much lower than that of the single boundary depending on the sign and value of the deviation parameters. The contrast of fringes will reverse when one changes the sign of deviation parameters for the matrix and/or the twin. Comparing with the well-known α-fringe and δ-fringe, overlapping twin fringes have special features which may arise from the anomalous absorption-anomalous transmission effects and the dynamic multiple beam interference among the matrix-twin-matrix or twin-matrix-twin. Using Van Dyck's iterative method, simulation images were calculated which are in good agreement with experimental observations.
1983, 32 (12): 1489-1496.
doi: 10.7498/aps.32.1489
Abstract +
In this work, the structure and chemical composition of thin films of white mica found in Si-Chuan Province are studied by transmission electron microscopy and scanning electron microscopy. The. thickness is in the range of 300-1000?. It is concluded that the sample is nearly perfectly crystalline and contains no detectable impurities, however some defects are discovered in certain regions as shown in the text (Fig. 2-4).Thin mica film can be used as a substrate on which other thin film can deposit or grow into large crystalline grains.
1983, 32 (12): 1497-1504.
doi: 10.7498/aps.32.1497
Abstract +
The fading phenomenon of pendellosung fringes in diamond crystals has been studied by means of X-ray diffraction section topography. The fading periods of dynamical interference frihges have been observed in plate-like crystal and wedge-shaped crystal, as well as in crystal containing a stacking fault. They have been adequately interpreted in terms of dynamical diffraction theory. The quantitative comparison of experiment with theory has been made and the agreement is found to be quite good.
1983, 32 (12): 1505-1514.
doi: 10.7498/aps.32.1505
Abstract +
The energy aberration of crystal monochromator in the case of continuous X-ray spectrum, for instance EXAFS, has been discussed. Based on the fact that the intensity of continuous X-ray varies slowly with the energy and can be treated as a constant, we propose a method of calculating average resolution for flat crystal and the Johann and Johansson arrangement. We have also pointed out some inappropriate points in analyses on the reflect geometry of Johann arrangement described in previous publications. It is shown that Johann crystal can provide a better resolution than that commonly believed.
1983, 32 (12): 1515-1525.
doi: 10.7498/aps.32.1515
Abstract +
We studied the second harmonic generation of light in LiNbO3 crystals with periodic laminar ferroelectric domains, in order to make a detailed experimental verification of the theory of quasi-phase-matching proposed by N. Bloembergen et al. First we determined the second harmonic light intensity of single domain LiNbO3 crystals in the regime eω ·eωe→e2ω. Then by using angle-scanning and temperature-scanning, we obtained the maximum second harmonic output from crystals with periodic domains corresponding to quasi-phase-matching. We have verified experimentally the relation that the second harmonic output is proportional to N2(N is the number of domains in the crystal) with N up to 200. We have compared the second harmonic output of crystals with periodic laminar domains in the quasi-phase-matching regime with that of single domain crystals of the same length and optical quality under phase-matched condition oω· oω→e2ω. An order of magnitude enhancement of second harmonic light output has been found. Finally, the structure sensitivity of the second harmonic generation of LiNbO3 crystal with periodic laminar ferroelectric domains has also been studied experimentally.
1983, 32 (12): 1526-1535.
doi: 10.7498/aps.32.1526
Abstract +
In this paper, the physical characterestics of the interaction in a gyrotron with a longitudinally varying magnetic field is presented. Equations of motion used in reference are improved by expressing them in normalized form and making them more accurate and more generally applicable. Numerical results are obtained for a pratical case. The physical mechanism of efficiency enhancement with varying magnetic field and its effect on the gyrotron operation are discussed. Phase bunching diagrams demonstrate that the saturation phenomena will be delayed when such varying magnetic field is present.
1983, 32 (12): 1536-1546.
doi: 10.7498/aps.32.1536
Abstract +
In this paper, the aberration theory for cathode lenses with combined electrostatic and magnetic focusing is discussed in detail. The more general case, when cathode is situated in both magnetic and transversal electric fields, has also been considered. Based on the variational principle, we have derived the general formulae of aberration coefficients of cathode lenses on any image plane, and transformed them into the linear combination of the well-known aberration coefficients given by Glaser. It follows that the aberrations for both the wide electron beam system (cathode lens) and the narrow electron beam system (conventional electron lens) can be treated by the universal variational theory. Hence the relationship between these two systems is also established.The paraxial electron trajectories of cathode lenses are described in the vector form. The aberrations are expressed in the matrix form, and they are suitable for computer calculation.
1983, 32 (12): 1547-1556.
doi: 10.7498/aps.32.1547
Abstract +
In this work, the phenomena of excitation of SWR (Spin Wave Resonance) in magnetic films are investigated. On the basis of Partis' Volume Inhomogeneity (Ⅵ) Model, the Asymmetric Volume Inhomogeneity (AⅥ) Model and the Surface-Volume Inhomogeneity (S-Ⅵ) Model are proposed. In terms of these models, we can explain satifactorily the linear spectra of SWE, in which the odd and even modes are excited simultaneously with their intensities changing in accordance with different envelopes.
1983, 32 (12): 1557-1564.
doi: 10.7498/aps.32.1557
Abstract +
The linear spin-wave spectra in Fe-Ni polycrystalline films and YIG single crystal films have been observed. It is found that in the spin-wave spectrum of magnetic film the odd and even modes are usually excited simultaneously, and their intensities change in accordance with different envolopes. Further investigations indicate that the positions and relative intensities of the odd and even modes vary with the depositing process and annealing of the film. All these experimental results can be well explained in terms of the Surface-Volume Inhomogeneity (S-VI) Model and the Asymmetric Volume Inhomogeneity (AVI) Model. In this paper the equipment and the relevant methods for measuring the spinwave spectrum are also described briefly.
1983, 32 (12): 1565-1573.
doi: 10.7498/aps.32.1565
Abstract +
Electrohydrodynamic instabilities of a planar nematic liquid crystal (εαα>0) under an inclined electric field (at an angle θ0 with the normal of the glass plates of the cell) are considered. On the basis of the one-dimensional theory of Dubois-Violette et al, conditions for the onset of instabilities under the excitation of static, sinusoidal and square wave electric Fields, respectively, are obtained. Major results include: (1) Relaxation time of charge increases monotonically with θ0. (2) For MBBA, there exists a critical angle θc(ω)(ω is frequency of external field), when θ0> θc(ω) instability cannot occur. θc(0) =54.2°. (3) For MBBA, threshold voltage is a monotonic increasing function of θ0.
1983, 32 (12): 1574-1585.
doi: 10.7498/aps.32.1574
Abstract +
In this paper, spherically symmetric structures of the Brusselator are calculated in detail by using the bifurcation theory. The results show that the solutions have both temporal-spacial dissipative-structures and a high coneentrative range in the centre of the sphere. These results will be greatly helpful in investigation of nuclear-type structures in biological and biochemical phenomena.
BRIEF REPORT
1983, 32 (12): 1586-1588.
doi: 10.7498/aps.32.1586
Abstract +
In this paper, we improve the model of the tuning fork antenna with collective mass, by developing a two-degree of freedom model to a three-degree of freedom one. Finally, the, experimental results of a prototype antenna are given.
1983, 32 (12): 1589-1594.
doi: 10.7498/aps.32.1589
Abstract +
It is shown that the inverse scattering transform method to solve the Lax pair of given nonlinear evolution equation can be reduced to a kind of Riemann-Hilbert (R-H) problem of meromorphic functions with respect to the complex spectral parameter. The R-H problem is generally regular no matter whether the solitons are involved in it. The linear singular integral equation connected with the R-H problem has been derived, which is essencially equivalent to the Gel'fand-Levitan-Marchenko equation. Furthermore, the regular R-H problem satisfied by the Darboux-B?cklund transformation from a fundamental solution set of the eigenvalue equation of Lax pair to a new set has been given as well. The R-H problem reduced from the inverse scattering transform is in fact a special case of that satisfied by the Darboux-Backlund transformation.
1983, 32 (12): 1595-1601.
doi: 10.7498/aps.32.1595
Abstract +
We studied the surface of stoichiometric α-Fe2O3 sample bombarded by Ar+ ion beam, the Fe++ ion was identified on it and the surface was found to become FeO-like in property. In addition, the results of UPS and XPS analysis indicated that OH-existed on the FeO-like surface during water adsorption and the Fe++ was the active center of water decomposition. We propose that water molecules adsorpted onto the surface can preliminarily be seperated into OH- and H+ due to the catalysis of 3d electrons of Fe++ ions on the surface. So, in order to raise the efficiency of photo-decomposition of water, it is not only important to modify the band structure, but also to create Fe++ ions on the α-Fe2O3 surface.
1983, 32 (12): 1602-1607.
doi: 10.7498/aps.32.1602
Abstract +
Based on the experiments about the Brazil twin appearing on -x plane {1120} of synthetic quartz, we have studied the formation mechanism of twinning by means of X-ray topography and electron probe micro-analysis and discussed the disadvantage in Kern's theory of nueleation dynemics of twinning. The new concept of strain barrier in twin boundary (SBTB) is proposed and it is considered that the crystal imperfection raises the energy state of the crystal itself and results in the decrease of height of strain barrier and easy formation of twin. We have also discussed the correlation of twinning with seed orientation, impurities and crystal defects in the light of crystal growth experiments and testing of crystal defects, and emphasized the influence of defects on twinning. Finally, the development of twin has been analysed from the view point of re-entrant corner growth mechanism.
1983, 32 (12): 1608-1612.
doi: 10.7498/aps.32.1608
Abstract +
The crystal structure of the ternary compound Y(Mn1-xCox)12 With x = 0.3, 0.5 and 0.6 is body-centered tetragonal of ThMn12 type. The space group is I4/mmm, z= 2. Powder neutron diffraction studies on this system has been performed to determine the possible ordering of the Co and Mn atoms on 3 nonequivalent crystallo-graphic sites 8i, 8j and 8f. The structure analyses at room temperature shows that the Co atoms tend to occupy the 8f sites primarily and then the 8j sites. They avoid the 8i sites when x is lower than 0.67. The experimental result is discussed and an inference is drawn.
1983, 32 (12): 1613-1617.
doi: 10.7498/aps.32.1613
Abstract +
Inelastic neutron scattering spectra from superconducting material C-15 V2Zr, V2Zr0.95Nb0.05 and V2Hf0.5Zr0.5,V2Hf0.5Zr0.3Nb0.2 were measured by neutron time-of-flight method. It was found that the additional content of Nb influenced the superconducting transition temperature Tc and phonon frequencies of V2Zr1-xNbx in a way different from that of V2Hf0.5Zr0.5-xNbx. The Tc increases and the phonon frequencies "soften" with increasing x for the former, while the Tc slightly decreases and the phonon frequencies "harden" for the latter. The result that the phonon frequencies of V2Zr0.95Nb0.05 are softer than that of V2Zr is somewhat in contradiction with the previous results, which show that the magnetic susceptibilities decrease and the geometric mean phonon frequencies increase. The result that the phonon frequencies of V2Hf0.5Zr0.3Nb0.2 are harder than that of V2Hf0.5Zr0.5 can be considered as the result of hybridization of conduction band, which is studied for close-packed compounds by means of LMTO (linear combination of muffin-tin orbitals) method.
1983, 32 (12): 1618-1622.
doi: 10.7498/aps.32.1618
Abstract +
In this puper, we report the synthesis of a new metastable phase La4Au by means of high pressure high temperature treatment of an amorphous alloy. As starting material, the La80Au20 amorphous ribbons were prepared from melt by rapid quenching method. Synthesis conditions were found to be at about 80kbar and 250℃. This new phase has a orthorhombic structure with lattice parameters a = 6.54?, b = 7.71? and c=11.32?, and exhibits superconducting transition at Tc=5.5 K which is higher than that of any known La-Au phases.
