摘要:

Ionized strontium is studied by the method of resonant absorption of optical radiation. Because of an accidental frequency overlap, normal rubidium can be used in a lamp as the source of resonant light. Spectral profiles of absorption were made with a scanning Fabry‐Perot interferometer. The 5s½−6p½ line of Rb and the 5s½−5p½ line of Sr+are found to differ by 0.014 Å. Optical and Langmuir probe measurements of density compare favorably. Ion temperatures in a steady‐state and a decaying plasma were determined from the Doppler width. Two different sources of ionized strontium plasma are described. Negative results were obtained in an attempt to optically pump strontium ions in a plasma.

ISSN:0021-8979    

DOI:10.1063/1.1714571

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Starting with CaF2containing Eu2+and Tm3+ions, we have employed optical techniques to observe the decrease in valence of the Tm ion under x irradiation. We find that the number of Tm2+ions produced corresponds closely to the number of Eu2+ions which disappear, and we suggest that the underlying mechanism is a direct transfer of an electron between the two types of ions.

ISSN:0021-8979    

DOI:10.1063/1.1714572

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The crystallographic aspects of silicon/corundum epitaxy were investigated. Epitaxial deposition was carried out on corundum substrates of two orientations, and the observed crystallographic relationships were shown to be determined by three‐dimensional matching between the silicon structure and the sublattice of possible cation sites in corundum.Single‐crystal silicon layers were deposited onto (0001) and (8¯629) corundum substrates. For growth on (0001) corundum, (111) silicon is parallel to the interface with [1¯10] silicon parallel to [2¯110] corundum. For growth on (8¯629) corundum, the silicon plane parallel to the interface is irrational, but the epitaxial relationship closely approximates to the following: (001) silicon parallel to (0001) corundum with [1¯10] silicon parallel to [2¯110] corundum.These two epitaxial relationships are the only ones which permit three noncoplanar symmetry axes of the silicon to coincide with three such axes of the cation site sublattice of the corundum. They insure compatible surface symmetries and similar surface densities on an arbitrary deposit/substrate interface. In general, the silicon atom density on the interface does not exceed the cation site density. When it does so, however, the rational crystallographic relationship is modified slightly in order to lower the density of silicon atoms below that of the possible cation sites.

ISSN:0021-8979    

DOI:10.1063/1.1714573

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The velocity of 180° domain walls in orthorhombic BaTiO3has been measured over a range of applied fields below 1 kV/cm in dc and in pulsed field conditions. From these measurements it was seen that the domain wall behavior was qualitatively very similar to that reported by Miller and Savage for the tetragonal case. The main difference was the more pronounced effect of the surface layer on the velocities of the walls in the orthorhombic crystals. Accordingly, a number of additional experiments were performed which gave more information on the nature of this surface layer. As a result a completely new model of the surface layer is proposed in which the activation field &dgr;Lin the layer is much higher than the activation field &dgr;Bin the bulk of the crystal. The predictions from this model are in satisfactory agreement both with the results reported here for orthorhombic BaTiO3and with all the evidence available from other sources of the behavior of tetragonal BaTiO3. Comparison is made with previously accepted models and it is shown that these fail to explain many of the experimental results both of the orthorhombic and of the tetragonal cases.

ISSN:0021-8979    

DOI:10.1063/1.1714574

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A cylinder of electrons infinitely long and infinitesimally thin in the radial direction is used to show the equivalence of the diochotron and negative mass instabilities. The electrons have a unique relativistic velocity in the azimuthal direction. The external magnetic field has a radial gradient, and a criterion for stability is derived that places a lower limit on the field gradient. This criterion shows that the instability can occur at energies below the transition energy of the magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.1714575

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The presence of a surface‐charge layer has been found in BaTiO3whiskers. A particular example is discussed where the surface‐charge layer completely dominated the properties of the whisker. A transition layer between the surface layer and the interior of the whisker was observed optically and found to be approximately 1 &mgr; thick. The domain structure of the whisker could be changed by applying an external axial electric field. The whisker always returned to its own unique equilibrium configuration when the field was removed. This equilibrium configuration was a direct result of the presence of the surface layer. The spontaneous polarization vector within the surface layer was saturated normal to the surfaces and toward the interior of the whisker. It was demonstrated both experimentally and analytically that this surface layer could cause spontaneous nucleation of spike‐shaped domains. These spikes extended through the surface layer and into the interior of the whisker. Nucleation occurred even in the presence of an opposing electric field. The magnitude of the potential drop across the surface layer apparently depends upon imperfections.

ISSN:0021-8979    

DOI:10.1063/1.1714576

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Arguments are presented which conclude that the mean density of mobile dislocations in a crystalline solid increases linearly with plastic strain for small strains and decays exponentially for large strains, all at constant stress and low temperatures. The resulting analytic expression combined with the strain‐rate equation can be integrated explicitly in terms of tabulated exponential integral functions. This creep equation has a general form that is consistent with many experiments and detailed comparison with a particularly well‐documented experimental curve yields quantitative agreement. The large strain limit of the proposed creep equation is the familiar logarithmic creep law. A simple transformation of the creep equation yields the shape of a slowly propagating plastic front, and it is shown that the predicted shape corresponds to experimental observations for mild steel. The lengths of the incubation periods that precede fast flow, as predicted by the equation, have a stress dependence that agrees with experiment. Finally, the present arguments together with previous ones yield a strain‐rate equation which generates both stress‐strain and strain‐time curves that are good reproductions of experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.1714577

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

It is shown that the fieldB= 22 kG which exists in each Weiss domain even in the absence of an applied field should cause certain anomalies in the residual resistance of very pure polycrystalline iron. The residual resistance in zero applied field is no longer proportional to impurity concentration. It may even have a minimum as a function of impurity concentration. The minimum should correspond to a resistivity ratioR273/R4.2of roughly 300. This explains why the resistivity ratio of samples of zone‐refined polycrystalline iron is usually found to be no higher than 200 or 300. The same internal field is also shown to be the cause of the resistance decrease in a small longitudinal field, observed in very pure iron and nickel at low temperature. A decrease is also expected in a small transverse field if the sample is very slightly misoriented.

ISSN:0021-8979    

DOI:10.1063/1.1714578

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

In metallic alloys the stress‐induced reorientation of solute pairs produces an anelastic relaxation called the Zener effect. To determine whether or not this relaxation is also observable in a nonmetallic solid solution, internal friction of single crystals of NaCl plus (1.3% to 1.7%) KCl is measured at 4 to 10 kc/sec. A maximum in the damping occurs near 400°C for nominally pure NaCl:KCl and near 300°C for NaCl:KCl crystals with CaCl2added to enhance the cation vacancy concentration. This behavior indicates that the Zener relaxation is present in NaCl:KCl. Diffusion constants calculated from this Zener relaxation agree well with the results of radioisotope diffusion experiments.

ISSN:0021-8979    

DOI:10.1063/1.1714579

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Phlogopite micas have been studied at high temperatures in the electron microscope and the observations related to the known behavior of micas to dehydrate, to undergo swelling over a wide temperature range, and to their anomalous thermal expansion. The specimens showed evolution of bubbles at room temperature and also on heating in the electron microscope. The bubbles are lenticular flaws from the separation of (0001) cleavage planes and these lenticular flaws exhibit intricate Bragg extinction contours. Areas of lenticular flaws frequently display complex diffraction patterns. The bubbles occur particularly on dislocation networks, tend to nucleate and grow at nodal points, and whole dislocation networks have been observed to convert at 700°C into large lenticular flaws It is shown that dehydration of mica can refer to two different processes. The first below 500°C is the removal of water molecules from between the silicate layers into lenticular flaws and the second above about 800°C is the escape of water from the mica by splitting of the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1714580

出版商:AIP    

年代:1965

数据来源: AIP