摘要:

Using a pulse method, the attentuation and velocity of longitudinal ultrasonic waves in nickel and cobalt are measured for frequencies 2, 3 and 6 Mc/sec from −78°c up to the Curie temperature range. At certain intermediate temperatures, peculiar peaks in attenuation accompanied by anomalies in velocity are observed. As the specimen is more and more magnetized, the peaks are found to diminish in height and suffer a slight shift towards higher temperatures. At technical magnetic saturation, the peaks do not collapse completely, a fact which differentiates the observed anomalies from those due to domain wall motion or domain rotation. An explanation for the origin of these anomalies could be found in the redistribution of spins, as an effect of the periodic mechanical stress, among the simultaneous stable directions of spontaneous magnetization inside the domain. This view is supported by a calculation of the corresponding temperatures of the peaks which agree fairly well with the experimental temperatures.

ISSN:0031-8086    

DOI:10.1080/14786436808227491

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

It is shown that (1) over a range of tip radii, the depth below a spherical surface where atoms of given coordination occur can be correlated with the thickness of the spherical shell which contains the atoms observed in a field ion image; (2) large changes in image intensity observed across certain zones correspond to abrupt asymmetrical changes in the atomic environment of the imaged atoms. The shortest possible bonds giving these changes correspond to first and fourth nearest neighbours in b.c.c. and third and fifth nearest neighbours in f.c.c.; (3) the changes in intensity across these zones become diffuse at small tip radii because a larger proportion of the image is derived from atoms with higher coordination. Their environment remains constant within a band extending some distance on either side of the zone.

ISSN:0031-8086    

DOI:10.1080/14786436808227492

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Experiments on slightly bent AgCl crystals, using an etch-pit technique to reveal dislocation sites, have shown that the behaviour on annealing depends on the size of the crystal sub-structure: when there is a fine sub-structure dislocations join the sub-boundaries but with a coarse sub-structure the dislocations form polygon walls. It is shown that dislocations of minority sign are introduced in bending.

ISSN:0031-8086    

DOI:10.1080/14786436808227493

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The electron microscope study of high temperature irradiation damage in single crystal and pyrolytic graphites has revealed differences in the defect nucleation behaviour which must be attributed to the differing crystallite perfection (Thrower 1967 a). A study of the formation and annealing of these defects, both vacancy and interstitial loops, has confirmed the earlier suggestion of Turnbull and Stagg (1966) that self-diffusion in graphite is three-dimensional. Furthermore, there are several pointers to this diffusion being by an interstitial mechanism. During both nucleation and annealing there is evidence of interstitial migration perpendicular to the basal planes, Analysis of these results gives a value of 6·55 ± 0·4 ev for the formation energy of an interstitial, and the implications of this value are discussed, the most important being that there must be a significant amount of bonding between the interstitial atom and the lattice.

ISSN:0031-8086    

DOI:10.1080/14786436808227494

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Dislocations introduced by plastic deformation in silicon do not produce the effects on the electrical properties which might be expected from their acceptor-like (in n-type material) or donor-like (in p-type material) behaviour, unless the deformation is performed at relatively low temperatures. When the plastic deformation, in this paper introduced by bending, is performed at high temperatures, the dislocations generated are easily contaminated and their corresponding electrical effects tend to disappear due to the compensation resulting from the contamination. It is suggested that oxygen is the contaminating impurity.

ISSN:0031-8086    

DOI:10.1080/14786436808227495

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Measurements of the transmission and reflection coefficients have been made on evaporated films of solid solutions of Pd in Cu, Ag and Au and Mn in Cu and Ag. In the ease of the Pd alloys additional absorption attributed to resonant bound states associated with the Pd d electrons has been observed. The location and breadth of these resonant levels have been determined for the Ag and Au alloys. In Cu the resonant state absorption overlaps the Cu absorption edge and is not separable. In the CuMn and AgMn alloys the bound d states of the Mn are known to be spin split. No evidence for the optical absorption due to these states has been found in CuMn which is interpreted as implying a very small splitting energy ∼0·25 ev per spin. Weak absorption is observed in the case of AgMn alloys and this is interpreted as indicating a spin splitting energy of ∼ 1 ev per spin. In all these alloys the absorption spectra of the matrix, particularly the characteristic edges of Cu, Ag and Au, are little affected by the addition of Pd or Mn solutes. Values of the optical effective mass are given and the significance of this quantity for the AgPd alloys is discussed.

ISSN:0031-8086    

DOI:10.1080/14786436808227496

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The low-temperature internal friction spectrum of gadolinium consists of two peaks, labelled α and β. The former is independent and the latter dependent on, the strain amplitude. Domain wall motion, induced by the applied stress, is responsible for both peaks, which are not caused by a relaxation mechanism. The microeddy currents generated by changes in magnetization are responsible for the α peak and from an analysis of the theory, a domain size of 10−3cm is deduced. The β peak is caused by the temperature variation of the magnetostriction constant and is essentially a hysteresis loss.

ISSN:0031-8086    

DOI:10.1080/14786436808227497

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Vapour phase grown ZnS single crystals were studied by x-ray topography. Low angle twist boundaries about [00·1] and ∼1′were found to be a characteristic feature of typical needle crystals having a faulted stacking sequence. Torsional stresses were applied to the crystals and produced similar boundaries up to 2° 36′. The critical shear stress resolved on the basal plane for plastic deformation of ZnS at 21°c was estimated to be 109dyn cm−2. The significance of the results with respect to the origin and properties of dislocations is discussed.

ISSN:0031-8086    

DOI:10.1080/14786436808227498

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The irradiation damage configuration and yield stress response obtained in the c.p.h. α’and α phases in a Zr-2·7% Nb alloy after fast neutron irradiation have been studied as a function of pre-irradiation solute distribution. Largest yield stress increments were obtained for specimens irradiated with the solute initially in metastable solution, pre-irradiation ageing treatments reducing the yield stress response. Electron microscope studies have shown that the irradiation damage configuration was also determined by the solute super-saturation in the alloy phases, maximum strengthening being associated with a population of defect clusters or loops of < 30 Å diameter. A mechanism for the defect stabilization effect is proposed.

ISSN:0031-8086    

DOI:10.1080/14786436808227499

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A study of the possibility of the existence of stacking faults in b.c.c. crystals on {110} and {112} planes has been performed, representing the lattice by a central force interaction between atoms. The same study was also carried out for {111} planes in f.c.c. crystals. The results for the f.c.c. lattice are in full agreement with the predictions based on a hard-sphere model. However, the results for the b.c.c. lattice are very different and suggest that no stable instrinsic stacking faults of the same type as in f.c.c. crystals can exist either on {110} or on {112} planes in b.c.c. crystals.

ISSN:0031-8086    

DOI:10.1080/14786436808227500

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor