摘要:

Measurements of the absolute thermoelectric powerSof very pure copper samples (with residual resistivity ratios as low as 3·1 × 10−4) have been carried out between ∼0·l°K and ∼350°K. Several specimens were found to exhibit marked negative anomalies inSbetween 8°K and 9°K, whereas a very pure sample of natural copper gave small but positive values ofSat low temperatures. By emphasizing thatSdepends on therelativeimportance of the various scattering mechanisms we have been able to show that the anomalies occur whenever scattering by traces of iron becomes dominant, other impurities being of only minor importance. Moreover we are able to account for the occurrences of similar anomalies, as well as the resistance minima, in dilute alloys of oxygen-containing copper with various solutes (e.g. Ga, Ge, Sn …)notin terms of these particular solutesdirectly, but only in so far as they separate traces of iron from its oxide, thereby bringing it into solid solution. At about 70°K there is a positive peak inSwhich we ascribe to an Umklapp phonon-drag component.

ISSN:0031-8086    

DOI:10.1080/14786436008241216

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Thin crystals of lead iodide grown from solution have been examined in transmission in the electron microscope. The crystals are sufficiently stable in the electron beam to allow dislocations to be observed, but it is found that after prolonged periods of observation at high beam intensities decomposition commences, and proceeds through a number of stages to completion. The initial and intermediate stages are accompanied by the climb of pre-existing dislocations, the formation of new dislocations and the creation of other features which might be interpreted as cavities in the crystal. These can be understood to some extent as a result of the formation of vacancies in the crystal under irradiation with the electron beam. In the final stage the crystals appear to decompose completely leaving an aggregate of dense crystallites which are probably metallic lead. This is presumably accompanied by the release of iodine gas. The mechanism for this final stage of decomposition is not yet understood.

ISSN:0031-8086    

DOI:10.1080/14786436008241217

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Experimental observations of the combination, in crystals of silver bromide, of two dislocations with Burgers vectors of 1/2a⟨110⟩ at right angles to form a single dislocation with a Burgers vector ofa⟨100⟩ are described in this paper. It is believed that this is the first occasion upon which the interaction has been definitely established for dislocations on glide planes.

ISSN:0031-8086    

DOI:10.1080/14786436008241218

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Measurements are reported of the diffusion of platinum at tracer concentrations in gold over the temperature range 800°c to close to the melting point of gold. Above about 900°c the results obtained can be fitted to the following equation :D= (7·6+4·7−2·9) exp [-(60 900 ± 1200)/RT] cm2/sec. The magnitude of the observed activation energy relative to that corresponding to self-diffusion in gold is in qualitative agreement with current theories.

ISSN:0031-8086    

DOI:10.1080/14786436008241219

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The application of strong electrostatic fields to bent LiF crystals producod small motions (0·1 to 6 Å) of the bends which were analysed in terms of the motion of charged dislocations. The charge on the dislocation core was positive and of the order of 10−4to 10−3e.s.u./cm, and it presumably arose from the inequality of the free energies of formation of positive ion and negative ion vacancies. Estimates of the electrostatic contribution to the critical shear strength based on these values of charge substantiate the suggestion by Eshelby, Newey, Platt, and Lidiard that much of this strongth may be electrostatic in origin.

ISSN:0031-8086    

DOI:10.1080/14786436008241220

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Electron microscope observations on the dislocation structure of cold-worked polycrystalline silver and on the processes occurring during annealing are described.

ISSN:0031-8086    

DOI:10.1080/14786436008241221

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The mean-square width of the nuclear magnetic resonance absorption line in copper sheet has been measured with an accuracy of ± 4%, using specimens from a sample of copper (99–98% Cu) on which stored energy measurements had already been made (Clarebroughet al.1957). Plastic deformation has been found to increase the mean-square line width by up to 40% and there is evidence that the bioadening is proportional to the stored energy. There is also a small reduction in the integrated intensity of the line in deformed specimens, possibly caused by the high strains in regions near the cores of dislocations.

ISSN:0031-8086    

DOI:10.1080/14786436008241222

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

FOB a number of years, among the outstanding problems in the study of lattice defects in f.c.c. metals there have been the properties of atoms on interstitial lattice sites as produced by cold-work or radiation damage. Considering copper as an example, the key problem was whether the energy of migration of interstitial atoms was about 0–1 ev or about 0–6 ev. In the first case, the interstitial atoms would anneal out below 60°K, whereas in the second case the so-called annealing stage III (at about 250°K) would have to be ascribed to the annealing out of the interstitial atoms. So far no specific experiment has been published that would demonstrate directly the presence or the behaviour of isolated interstitial atoms in f.c.c. metals. The two views mentioned above are based on the analysis of a large body of experimental material, the interpretation of which includes the assignment of migration and formation energies to lattice defects other than interstitials. Recent reviews emphasizing the one or the other of the two principal viewpoints are those by Seitz (1959; small migration energy of interstitials) and by Seeger (1058, 1960; large migration energy of interstitials).

ISSN:0031-8086    

DOI:10.1080/14786436008241223

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Vibrational frequency spectra of sodium chloride derived from two theoretical models which allow for ionic deformability, instead of treating the ions as rigid point charges, have been used to calculate effective Debye temperatures and distribution function moments.

ISSN:0031-8086    

DOI:10.1080/14786436008241224

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

IT is well known that metals such as copper may show anomalous resistive and thermoelectrio behaviour at low temperatures. It now seems clear (cf. Goldet al.1960) that the large negative thermoelectric power which develops at temperatures of the order of 10°K to 20°K in certain specimens of the ‘pure’ metal or specially prepared dilute alloys must be attributed primarily to the presence of very small quantities of iron in solid solution. It also appears that other magnetic ions in solid solution will give rise to similar behaviour (cf. e.g. Jacobs and Schmitt 1959). It has been suggested (Schmitt 1956, cf. also Brailsford and Overhauser 1959) that, for example, the appearance of a maximum (and consequently also a minimum) in the electrical resistance at low temperatures can be explained in terms of scattering by magnetic impurity ions, if the spin degeneracy of the ground state is split and the electron scattering cross sections of the lower levels are higher than those of the upper levels. No detailed analysis appears to have been made of the thermoelectric behaviour to be expected on such a model, but it is suggested (cf. Schmitt loc. cit.) that this might be predicted if due account is taken of the inelastic electron scattering involved. One might remark that the experimental situation is to some extent complicated by the fact that electron scattering by excited lattice vibrations (phonons) becomes important above, say, 15°K in Cu in comparison with electron scattering by impurity sites.

ISSN:0031-8086    

DOI:10.1080/14786436008241225

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor