摘要:

Following a report of ferroelectricity at room temperature in Na(Nb1−xVx)O3, crystals of pure NaNbO3and Na(Nb1−xVx)O3have been investigated electrically, optically, and by x‐ray diffraction. Attempts to introduce amounts of vanadium larger thanx≈0.005 into the crystals were unsuccessful. The room temperature phase of pure NaNbO3has been reported to be antiferroelectric, that of NaVO3nonferroelectric but perhaps also antiferroelectric. The vanadium‐doped crystals appear to be antiferroelectric in the room temperature as grown state. A transition to a ferroelectric phase can be induced in both the vanadium‐doped and the pure crystals by a sufficiently high field (of the order of 50 kv/cm), called thetransition field, applied normal to the orthorhombicbaxis. In one type of crystal plate, when the field‐induced transition into the ferroelectric phase occurs, a crystallographic reorientation is also observed. Some crystals revert to the nonferroelectric phase when the transition field is removed.All of the crystals investigated while in the ferroelectric phase were found to have the length of thebaxis twice the length of the simple perovskite cube, whereas in the antiferroelectric phase, the length of thebaxis is four times that of the simple perovskite cube.In so far as the phenomena studied in the present investigation are concerned, it can be stated that the vanadium‐doped crystals behave in most respects like pure NaNbO3crystals. In particular, no evidence was found for an unbalanced antidipole configuration, i.e., ``ferrielectric'' structure, proposed by another investigator in an earlier paper. Further differences between the content of that paper and the present results are pointed out.

ISSN:0021-8979    

DOI:10.1063/1.1728800

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The elastic displacement field around a uniformly moving edge dislocation has been obtained for the case where the dislocation glides on a (111) plane in a ⟨110⟩ direction in an anisotropic face‐centered‐cubic crystal. An equation is obtained for the velocity (the Rayleigh wave velocity) at which the shear stress on the slip plane of a moving dislocation is zero. Dislocations of like sign moving at velocities faster than this velocity attract rather than repel each other. It is concluded that when anisotropy is small and the elastic constantc11is smaller thanc12+2c44(the more commonly occurring relationship between the elastic constants) the Rayleigh wave velocity is increased above its value in an isotropic crystal and therefore, the extent of the velocity region where dislocations exhibit an anomalous behavior is decreased. For slightly anisotropic crystals the limiting velocity of dislocation motion is the slower of the two shear velocities in the ⟨110⟩ direction.

ISSN:0021-8979    

DOI:10.1063/1.1728801

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Calculations have been made of the shear stress produced by an edge dislocation moving on its slip plane in aluminum, copper, silver, gold, lead, and nickel. It is found that, except in the case of aluminum, the anomalous velocity range in which dislocations of like sign attract one another is very small. It is concluded that the effect of anisotropy in decreasing the extent of the anomalous velocity range is much greater in face‐centered‐cubic than in body‐centered‐cubic metals.

ISSN:0021-8979    

DOI:10.1063/1.1728802

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Heat transfer intensity and current density distributions at the anode of high current arcs in predominantly inert gas atmospheres were determined experimentally. Measurements were made for stable, axially symmetric arcs having a small diameter refractory metal cathode and a plane, cooled copper anode. The experimental method consisted of splitting the anode, measuring the heat flux and the current to one of the sections as a function of arc position relative to the splitting plane, and calculating therefrom the distribution functions. The work encompassed the effects of gas pressure (195–790 mm Hg), cathode geometry and material (tungsten and W‐1% ThO2), electrode separation (1.6–12.7 mm), arc current (100–300 amp), gas composition (argon, helium, and diatomic gas‐argon mixtures), and localized constriction of the plasma column. Peak heat transfer intensities ranged from 1.0 to 20 kw/cm2and peak current densities from 100 to 2500 amp/cm2. The heat and current distribution curves were of similar shape and were generally sharper than Gaussian. The heat distributions were partially resolved according to transfer mechanism. An upper limit was set on the average kinetic energy of electrons arriving on axis at the anode. This was used to specify limits on gas heat transfer intensities for certain conditions. The space charge sheath at the anode was estimated to be 10−4to 10−3cm thick at the arc axis.

ISSN:0021-8979    

DOI:10.1063/1.1728803

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Charge multiplication arising from carriers injected intop‐njunctions in gallium phosphide has been studied as a function of applied bias. From these and capacitance studies, the carrier ionization rate as a function of field has been determined. It is found to be very similar, both qualitatively and quantitatively, to the behavior in silicon. In particular, the mean free path for hot carriers between collisions involving optical phonon emission is of the order of 100 A. An additional result obtained from simple analysis of the photoresponse and capacitance behavior of the junctions is that the dominant carrier lifetime is 10−10sec.

ISSN:0021-8979    

DOI:10.1063/1.1728804

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

During the drive phase of the operation of a flux‐limited multipath core the flux change produced in the driven branch is the irreversible flux available to that branch plus a certain amount of reversible flux. Most of this flux will return through the shortest path in that part of the magnetic circuit of the core which constitutes the load for the driven branch. It is shown, however, that if the irreversible flux of some branch of this path saturates, the additional flux from the driven branch will produce an irreversible flux change in the next shortest path. This flux change reappears as noise during the reset phase. This fact leads to the surprising result that under some circumstances a greater flux change occurs in the longer branch of the load structure of a three‐rung laddic than in the shorter. This source of noise may in many cases be circumvented by reducing the cross section of the driven branch. These ideas are applied to explain the existence of optimum hold currents in the general laddic. A modification of the geometry of the three‐hole memory core which improves the signal‐to‐noise ratio in inhibited‐flux operation is described.

ISSN:0021-8979    

DOI:10.1063/1.1728805

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The diffusion of copper in polycrystalline Ag2Se was determined from measurement of the rate of change of the resistivity profile of a partially copper‐plated ingot of the semiconductor material. The copper concentration profile that was determined from the resistivity profile, was found to agree very satisfactorily with a theoretical concentration curve computed from a normalized complementary error function. The room temperature diffusion coefficient of copper in Ag2Se was computed from these data and was found to be 4.7×10−8cm2sec−1.

ISSN:0021-8979    

DOI:10.1063/1.1728806

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The rapid evaporation or condensation of a vapor bubble when out of equilibrium compared to the slow dissolving or growth of an air bubble results in quite different propagation properties of sound waves through water containing one or the other types of bubbles. Adapting a method developed by Foldy in his treatment of the air bubble case, we derive an expression for the propagation number for sound waves in a ``vapor bubbly'' medium. As an application of the theory it is shown that as few as 10/cm3vapor bubbles of radius about 10−3cm will (for ambient pressure about one atmosphere) attenuate an ultrasonic (f=˙3·104cps) sound wave by a factor of 10 in 10 cm. Suggestions are made concerning the use of these waves for the early detection of shut‐down bubbles following a power burst in a reactor.

ISSN:0021-8979    

DOI:10.1063/1.1728807

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Diffusion coefficients of Al26and Mn54in aluminum have been determined between 450° and 650°C. Low specific activities of the isotopes necessitated use of a thick layer technique. The exact solution to Fick's second law for the appropriate boundary conditions was used in treating the data. Temperature dependence of the diffusion coefficients may be expressed by the following equations:DAl26=1.71 exp−(34 000/RT)DMn54=0.22 exp−(28 800/RT).

ISSN:0021-8979    

DOI:10.1063/1.1728808

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The effect of adding the rare‐earth elements to cobalt, iron, and nickel has been investigated. Antiferromagnetic coupling was found to exist in the cobalt and iron rare‐earth compounds. The moment per formula unit of the compound Co5Y is increased when Sm, Pr, and Nd are substituted for yttrium and decreased when Tm, Gd, Tb, Er, Dy, and Ho are substituted. This is explained on the basis that although the spin moments of cobalt and rare earths are coupled antiferromagnetically in these compounds, the orbital moments add to the cobalt moment in the compounds containing Sm, Pr, and Nd, but they subtract from the cobalt moment in the compounds containing Tm, Tb, Er, Dy, and Ho. For the iron compounds investigated, the moment of the compound Fe4Y was found only to decrease when Tm, Er, Ho, and Dy were substituted for yttrium. The nickel compounds behaved entirely differently from the cobalt and iron compounds since very little or no antiferromagnetic coupling was observed in these compounds.

ISSN:0021-8979    

DOI:10.1063/1.1728809

出版商:AIP    

年代:1962

数据来源: AIP