摘要:

Measurements of the thermal conductivity of plastically deformed CaF2and LiF between 1.3° and 80°K indicate the presence of a phonon scattering mechanism which does not display the frequency dependence normally associated with dislocations. Instead of a reciprocal relaxation time &tgr;−1∝&ohgr;, which is characteristic of scattering due to individual dislocations, it is found that a stronger frequency dependence is indicated. Furthermore, a large anisotropy in the conductivity of CaF2is evident from the results obtained when the temperature gradient is parallel to the strongly oriented edge dislocations, as contrasted to when the gradient is perpendicular to them. It is suggested that dislocation dipoles, composed of pairs of edge dislocations of opposite sign and of dipole spacing comparable to the dominant phonon wavelength, are the cause of the observed effects. There is strong evidence for cross‐glide in these materials, and an examination of the etched surface of deformed CaF2reveals many etch pits which are sufficiently close together to indicate that, as a mode of dislocation multiplication, cross‐glide produces dipoles which could be responsible for the observed departure from normal dislocation scattering.

ISSN:0021-8979    

DOI:10.1063/1.1702973

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

It is shown that in the solution of electromagnetic problems the compressibility of a medium can be characterized by a ``compressivity tensor,'' just as a permittivity tensor is used to characterize anisotropy. The effects of a compressible medium can be accounted for by a ``pressure displacement current,'' which depends on the spatial variation in pressure, and by an equivalent volume density of charge, which is proportional to the pressure deviation from the mean. The constitutive parameter tensors are given in both dyadic and matrix forms. With the suggested representations, the solution of electromagnetic problems in an anisotropic and compressible plasma can proceed on a systematic basis. It is also shown that with a constant, externally applied magnetic field, the electromagnetic fields can be decomposed into longitudinal and transverse components. A complete formal solution is given for the case where there is no longitudinal variation.

ISSN:0021-8979    

DOI:10.1063/1.1702974

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The direct energy gap in PbTe has been deduced over the range 3.5°≤T≤300°K, from the spectral dependence of short circuit photocurrent in grownp‐njunctions. At temperatures above ∼30°K, the deduced absorption in the depletion region is found to be exponential, with the steepness of the edge dominated by thermal broadening. At lower temperatures, the effects of broadening due to the electric field within the junction depletion region have been observed. A third broadening mechanism is observed at low temperatures. At 5.8°K, this mechanism is of approximately equal strength to the thermal broadening. The energy gap, taken from the photon energy at which the photocurrent has fallen to one‐half its maximum value, at which point the absorption coefficient &agr;=14 cm−1, is given byEg=0.173+0.485×10−3TeV for temperatures 30°<T<250°K. Below ∼10°K, the energy gap has a constant value of 0.185±0.002 eV.

ISSN:0021-8979    

DOI:10.1063/1.1702975

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The interactions between Ni and NiO were investigated by examining the magnetic properties of Ni films on single‐crystal NiO substrates. The orientations of the NiO substrates were (001) (compensated spin planes), and (111) (parallel spin planes). With (001) NiO the Ni films were strained an amount corresponding approximately to the rhombohedral deformation of NiO below its Ne´el temperature. The amplitude and symmetry of magnetic torque data were consistent with the magnitude of this strain and the symmetry of the antiferromagnetic domain structure, respectively. Ni films on (111) NiO substrates had a complex field dependence of rotational hysteresis. This behavior was analyzed in terms of exchange anisotropy coupling and the interaction of the field with both the Ni and NiO spin systems. The analysis provided good agreement with the data for an exchange anisotropy energy of 1.75 erg/cm2of interface, a crystalline anisotropy of NiO in its parallel spin plane of 1.1×103erg/cc NiO, and a ``flop field'' for NiO in its parallel spin plane of 5 to 10 kOe. The analysis showed that two new regions of rotational hysteresis loss are present in fields ≥ the ``flop field'' of the antiferromagnetic spin system. Some more general features of exchange anisotropy coupling are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1702976

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Single crystals of magnesium fluoride, grown by the Czochralski technique, have been examined by means of chemical etching, and optical and electron microscopy. Dislocations in as‐grown crystals are found to be decorated with precipitates; the nature of the precipitates has been investigated. Grown‐in dislocations and undecorated dislocations introduced by slip can be etched in hot sulfuric acid. Etch pits at grown‐in dislocations often exhibit characteristic ``beaks'' or ``tails.'' Chemical etching has been used to establish the existence of three slip systems, namely {110}⟨001⟩, {001}⟨100⟩, and {101¯}⟨101⟩.Specimens for examination by transmission electron microscopy were prepared by chemical dissolution after mechanical shaping. Grown‐in dislocations are normally removed by unavoidable selective etching. In the microscope the samples are damaged by the electron beam. Point defects are produced which aggregate and result in both dislocation loops and precipitate platelets.

ISSN:0021-8979    

DOI:10.1063/1.1702977

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702978

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702979

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702980

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702981

出版商:AIP    

年代:1965

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1702982

出版商:AIP    

年代:1965

数据来源: AIP