摘要:

A crystal of cobalt ferrite was grown from the melt at 1600°C under an oxygen pressure of 790 psi. Chemical analysis of a portion of the crystal gave a ferrous ion content of 1.3%.

ISSN:0021-8979    

DOI:10.1063/1.1736130

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Penning discovered many years ago that a discharge whose characteristics depend on maintenance of a population of metastables can have its operation altered drastically when the metastables are removed by incident light. We have re‐examined the effect in the light of more modern techniques with a view toward developing a highly efficient, narrow‐band photodetector. A detector has been built which has sensitivity for the 20 581‐A line of He comparable with that of commercially available detectors, but an acceptance bandwidth of only 0.1 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.1736131

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A model is considered for the case of polycrystalline ferroelectrics in which each crystallite is presumed to behave according to a free‐energy function of the type formulated by A. F. Devonshire [Advances in Phys.3, 85 (1954)] for BaTiO3. The Curie temperatures for the individual grains are taken in a Gaussian distribution about some chosen temperature. The permittivity is obtained by averaging with this distribution over all of the crystallites. In accordance with the free‐energy function, it is assumed that the electric field induces a ferroelectric axis in those crystallites of the distribution which are not ferroelectric at a given temperature. On the basis of experimental evidence, 90° reorientation of domains in the ferroelectric part of the distribution is presumed to be negligible for semistatic and dynamic fields. Despite the seemingly severe restriction imposed by the latter assumption, a large field sensitivity is predicted. Agreement between the theory and experimental data is excellent for both parallel and transverse fields. It is concluded that the variation of incremental permittivity is associated with an induced ferroelectric state rather than being directly a property of domain processes, and that a large variation with field must necessarily be accompanied by strong thermal sensitivity.

ISSN:0021-8979    

DOI:10.1063/1.1736132

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

It is shown that in the cathode drop region of a metal vapor arc, there are four equations and two limiting conditions relating five dependent variables. The five dependent variables treated are temperature of the cathode spot, electric field at the cathode, total current density, current density carried by electrons, and the radius of the spot. When these equations are combined, a current level is found below which no solution exists. It is proposed that this current corresponds to the point at which a vacuum arc extinguishes in an alternating‐current circit. Experimental measurements of the current level at which this event occurs have been made, and the results are compared with the theoretical calculations.

ISSN:0021-8979    

DOI:10.1063/1.1736133

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

An analysis is presented which suggests that the ``ankle energy,'' that is, the energy at which the experimental sputtering ratio curve begins to form a low‐energy tail, is the maximum energy which the metallic lattice can propagate in a close‐packed direction. The effect appears to depend only upon the existence of a chaining threshold, and not upon the mathematical model of the sputtering process. The equivalence is demonstrated for the author's statistical model, and for the primary lattice ion model of Kinchin and Pease [G. H. Kinchin and R. S. Pease, Repts. Progr. in Phys.18, 1 (1955)].

ISSN:0021-8979    

DOI:10.1063/1.1736134

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Measurements have been made for all six third‐order elastic moduli of germanium by measuring ultrasonic velocities in selected directions when directed static stresses are applied to the crystal. Three measurements are obtained by using hydrostatic pressures, three by using a static compression along the <001> axis, and six by stressing the <110> axis with measurements being made along the <001> direction and the <11¯0> direction. Using the finite strain formulas of Murnaghan, the measured velocities are related to the three second‐order elastic moduli and the six third‐order elastic moduli for a cubic crystal. The 12 sets of measurements provide considerable overlap, and the probable errors are shown to be moderate.

ISSN:0021-8979    

DOI:10.1063/1.1736135

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Thermodynamical considerations on the vapor‐phase growth of whisker and platelet crystals of &agr;‐Al2O3by the oxidation of aluminum lead to the conclusion that the vapor‐phase mass transport is probably due to the suboxide Al2O and not AlO as previously suggested. Electron microscope observations confirm the optical evidence that spiral growth steps do not occur on the (0001) surfaces of Al2O3crystals grown in this way.

ISSN:0021-8979    

DOI:10.1063/1.1736136

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

When Armco iron is loaded with a transient wave in which the pressure exceeds 0.131 megabar, smooth spalls may be observed. The two distinct compression shocks which are transmitted by the iron are followed by a steep rarefaction which may be called a rarefaction shock. At a free surface, the first compression shock is reflected as a backward‐facing rarefaction wave. This wave may also steepen into a rarefaction shock which eventually meets the forward‐facing rarefaction shock. The interaction of these waves results in a localized tension of destructive magnitude, which produces a smooth fracture. Location of the plane of this interaction was calculated by applying the theory of hydrodynamics. These calculations are inexact because the speed of sound for relief waves was taken from Hugoniot data since other data are not available. Fair agreement was obtained between experimental and calculated results. The work indicates that, in the case of a double spall, the fracture most remote from the original free surface may sometimes be formed first.

ISSN:0021-8979    

DOI:10.1063/1.1736137

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Temperature gradients in the range 2000°C/cm–3000°C/cm have been imposed across the interface of binary diffusion couples fabricated from fcc metals. The systems investigated were Au&sngbnd;Ni, Cu&sngbnd;Ni, &ggr;Fe&sngbnd;Ni, &ggr;Fe&sngbnd;Pd, and Ni&sngbnd;Pd. It was found that chemical diffusion in these systems was influenced in varying degrees by the temperature gradient. Suggestions are given for the manner in which the temperature gradient may affect the various contributions to chemical diffusion.

ISSN:0021-8979    

DOI:10.1063/1.1736138

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Ten compositions were prepared in the systems As:Se:Te and As:S:Te. Nine of these compositions were amorphous in structure. The resistivities and Seebeck coefficients of these materials were measured as functions of temperature. The resistivity varied exponentially with temperature, while the Seebeck coefficient varied linearly. At 298°K, the resistivity values for the amorphous samples ranged from 4.7×104−2.5×1013ohm‐cm, while the Seebeck coefficient values ranged from 830–1625 &mgr;v/°K (ptype). At any temperature, the resistivity decreased with increase in tellurium content. For the amorphous materials, the thermal conductivity values ranged from 2.4–4.4 mw/cm‐°K.

ISSN:0021-8979    

DOI:10.1063/1.1736139

出版商:AIP    

年代:1961

数据来源: AIP