摘要:

A refined analysis of dislocation energy and dislocation networks in {110} planes of &agr;‐iron crystals is presented on the basis of anisotropic elasticity.Contrary to the conclusions given by isotropic theory, the elastic energy per unit length of a screw segment, with Burgers vectora⟨100⟩, is greater than that of an edge segment with the same Burgers vector lying in a {110} plane. The latter in turn is greater than the sum of the energies of two screw segments with Burgers vector (a/2)⟨111⟩.The shape of a stable net composed ofa⟨100⟩ screw segments and (a/2)⟨111⟩ segments of mixed character in {110} planes is determined by the line tension method. Comparison between theory and experiment is discussed. It is shown that the anisotropic theory agrees well with the observations.

ISSN:0021-8979    

DOI:10.1063/1.1714324

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Measurements of ionic conductance and electron lifetimes have been made on the grains of two AgBr photographic emulsions, one composed of regular octahedral grains bounded by (111) planes and the other composed of regular cubical grains having (100) faces. The field decays more slowly in the cubical grains, indicating that crystal habit affects ionic conductivity. Electron lifetimes were observed to be approximately equal to the field decay in the octahedral grains and shorter than the field decay in the cubical grains, in contrast to the tabular grains measured previously, in which the electron lifetime was longer than the field‐decay time. An explanation for this is proposed, based on the assumption that the interstitial silver ions are inhomogeneously distributed in the volume of the grains.

ISSN:0021-8979    

DOI:10.1063/1.1714325

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Light‐scattering measurements were made on a number of phase‐separated glasses in which the number and size of the particles of the new phase were varied. Plots of scattering intensities versus scattering angles showed two unique features: (1) higher scattering intensities were found in the back angles and (2) in some cases sharp maxima in intensities were found. In the first case the experimental data were in excellent quantitative agreement with Goldstein's theory for scattering from systems in which the growth of the new phase is diffusion controlled. In the second case the data were explained using Rayleigh‐Gans theory of light scattering for spheres and Frank's theory for diffusion‐controlled growth. The results confirmed the existence as well as the extent of the composition gradient around the growing particles as predicted by diffusion‐controlled growth theory.

ISSN:0021-8979    

DOI:10.1063/1.1714326

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The five independent elastic constants of single crystals of hexagonal close‐packed rhenium have been determined by the ultrasonic pulse‐echo technique over the temperature range 4.2°–298°K. The values at 298°K in units of 1011dyn/cm2areC11=61.25,C33=68.27,C44=16.25,C12=27.0, andC13=20.6. The bulk modulus derived from these constants shows a temperature variation somewhat analogous to that which has been reported for other 4d–5dtransition metals. The Debye temperature calculated from the elastic constants at 4.2°K is 416.2°K.

ISSN:0021-8979    

DOI:10.1063/1.1714327

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Thegfactor of polycrystalline magnetite was measured at liquid‐nitrogen temperatures and atK‐band frequencies. A high value of 4.06 for thegfactor was obtained for the stoichiometric composition. Thegfactor gradually changed to 2.29 as the oxygen concentration of the sample was increased above the stoichiometric composition.

ISSN:0021-8979    

DOI:10.1063/1.1714328

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

When Pt‐, Cu‐, and Zn‐phthalocyanines are vacuum‐evaporated onto cleavage faces of muscovite, single‐directional orientation occurs at lower substrate temperature. At higher temperature ranges, Zn‐phthalocyanine has a double‐directional orientation while Pt‐ and Cu‐phthalocyanines show triple‐directional ones. High‐resolution electron diffraction patterns, which were well‐defined fiber diagrams, revealed that all three compounds showed conspicuous isomorphism with one another, and Zn‐ and Cu‐phthalocyanines occurred in the metastable forms of their dimorphs. General crystal structures of metastable forms are discussed on the basis of the found isomorphism with Pt‐derivative.Evaporated films were composed of lamellar crystal strips, and the fiber diagrams showed that at least two kinds of lattice orientations were assumed by all three compounds, while the longitudinal crystal axis of individual strips always ran parallel to theirbaxes.As to relative orientation of the evaporated films to the substrate, thebaxis of the former was parallel to either of the two directions which made ±60° with theaaxis of muscovite in the case of the single‐directional orientation. When the evaporated films had double‐ or triple‐directional orientations, the electron diffraction pattern showed twofold symmetries in spite of the apparent triangular configuration. It turned out that this axis of twofold symmetry also coincides with the same axis of muscovite as above. It is presumed that the unique orientation axis of the evaporated films coincides with the staggering direction of the two oxygen tetrahedron sheets in the top subcell of muscovite. Plausible origin of these orientations are also discussed in terms of lattice vibration near the surface.Lattice imperfections of the evaporated films were directly observed in the lattice image obtained by the high‐resolution electron microscopy. The dislocation density seems rather high when compared with other similar lamellar crystal strips of the same compounds formed by colloid chemical methods. This was ascribed to the crystal formation controlled by the epitaxial effect.

ISSN:0021-8979    

DOI:10.1063/1.1714329

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Calcium tungstate deforms by slip on the (001) ⟨100⟩ system above 400°C. Simple shear over this plane is the only deformation mode observed under compression at temperatures up to 900°C and a strain rate of 10−3sec−1. The critical resolved shear stress is strongly temperature dependent. Crystals cannot be plastically deformed at room temperature, at 400°C they are still quite brittle but by 900°C they are soft (yield stress, 500 psi) and plastic. Slip traces at all temperatures are fine and straight but those produced at lower temperatures (600°–700°C) have a greater surface tilt and are more sharply defined than those produced above 800°C. This is due to fewer dislocation sources and restrictions on dislocation multiplication at lower temperatures.The role of bonding and crystal structure in the selection of slip parameters is discussed. It is considered that the stacking of the oxygen ions is the dominant factor dictating the slip plane and slip direction. Slip cannot occur without some distortion of the covalently bonded WO42−radical, which probably accounts for the strong temperature dependence of the critical resolved shear stress. It is shown that relatively easy slip in a given [100] or [010] direction can only occur between every other pair of (001) planes. Thus, a jogged dislocation which is mobile on one plane will become immobile on the next (or any odd number) plane. This is considered to restrict dislocation multiplication at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1714330

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The relationship between shear cracks and double‐ended dislocation arrays is discussed. The density of a double‐ended dislocation array under the uniform applied shear stress was calculated by the shear‐crack conversion method. The calculated density agrees with that calculated from the dislocation model. A general method of calculating the dislocation densities near the spearheads of dislocation arrays is given. Examples are illustrated; in general, the density as well as the stress and strain fields near the spearhead of a single‐ended linear dislocation array are higher than those of a double‐ended array under the same applied stress on the slip plane.

ISSN:0021-8979    

DOI:10.1063/1.1714331

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Magnesium oxide crystals have been examined in an ultramicroscope and the arrangements of precipitate particles in the material are illustrated. Unusual dislocation configurations are revealed by decoration in certain crystals.It has been suggested in the literature that most precipitate particles in magnesia are of zirconium oxide. The present observations of particle density indicate that it is unlikely that this is completely true at least for heat‐treated samples, even if the particles are finer than has formerly been assumed.

ISSN:0021-8979    

DOI:10.1063/1.1714332

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Individual edge dislocations created by heat treating indentations on thenside of a shallow phosphorus‐diffused siliconp‐njunction have been detected by the scanning electron beam technique. The width of contrast produced by edge dislocations is close to 1 &mgr; in agreement with expectation. The contrast mechanism is discussed and can be explained by enhanced recombination at dislocations with an edge component. Furthermore, it is shown that oxygen precipitates in silicon can be displayed as well as individual dislocations introduced by twisting the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1714333

出版商:AIP    

年代:1965

数据来源: AIP