摘要:

The addition of the solutes cadmium, indium, and tin to silver increases the probability of deformation faults &agr; in filings from 3×10−3in pure silver to a maximum value of 45×10−3at the highest concentrations of solute. In addition, the twin fault probability &bgr; measured from center of gravity displacements varies from 10×10−3for pure silver to 30×10−3for the alloys highest in tin or indium concentration. Lattice parametersahklwere determined from all available reflections of the cold‐worked and annealed specimens and plotted as a function of cos2&thgr;/sin&thgr;. By relating the large scatter of the individualahklto the occurrence of deformation faults in the deformed material, the true lattice parameter,a0(CW), and the deformation fault probabilities &agr; of cold‐worked materials could be determined. There was an apparent decrease in lattice parameter of the deformed Ag‐Sn alloys which was largest (∼0.1%) for the greatest tin concentration (Ag‐9%Sn). Using Fourier analysis of line profiles, the effective particle sizes (De)hkland root mean square strains [⟨&egr;L2⟩av]hkl½were determined. The measured effective particle sizes were anisotropic [(De)111/(De)200=1.7] and are primarily a consequence of deformation and twin faulting. The values for the compound fault probability (1.5&agr;+&bgr;) from peak shift and asymmetry and from anisotropic particle sizes, i.e., from peak broadening, agreed rather well.

ISSN:0021-8979    

DOI:10.1063/1.1702428

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An experimental investigation of the effects of formation conditions on the structural characteristics of thin Ge films vacuum deposited onto synthetic single crystals of CaF2, NaCl, NaF, and MgO is reported. Formation conditions include substrate temperature during deposition, rate of deposition, and heat treatment. The amorphous to crystalline transformation of Ge was found to occur in the 300–350°C substrate temperature range. It is shown that single‐crystal films, 1500 Å thick, can be formed on CaF2substrates at temperatures between 450° and 700°C by proper choice of rate of deposition. Crystalline structure, porosity, complexity of imperfections, and film adhesion are dependent on the rate of deposition and deposition temperature.

ISSN:0021-8979    

DOI:10.1063/1.1702429

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Factors affecting the power density of optimally bundled electron beams used for the welding, cutting, and machining of solid material are described. The power density and spot size of these beams are expressed as a function of acceleration voltage, beam current, and electron optical characteristics of the system. Assuming that the spherical aberration of the beam‐focusing lens system limits the spot size of the space‐charge‐limited beam, the power density under optimum conditions increases approximately with the fifth power of the acceleration voltage, and decreases with the 7/4 power of the beam current.A criterion is also given which enables one to determine whether the electron beam at its impact on the workpiece is space‐charge‐limited or not. Some considerations are given to the neutralization of the electron space charge by ions originating from the background pressure of the vacuum system.

ISSN:0021-8979    

DOI:10.1063/1.1702430

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Some liquids and solutions become doubly refracting and behave as uniaxial crystals when traversed by acoustic waves of high frequency. In many aspects the induced birefringence is analogous to birefringence due to flow. Theories for this behavior are presented and discussed in detail. For liquids and solutions of flexible macromolecules the birefringence is proportional to the square root of the acoustic intensity and to the frequency of the wave, but for colloidal solutions it varies directly as the intensity and is independent of frequency. It is shown that from measurements of the birefringence, values of relaxation times and diffusion constants can be obtained. The method has a number of advantages over flow birefringence studies and in common with the latter does not depend on the possession of a permanent dipole moment by the molecules.

ISSN:0021-8979    

DOI:10.1063/1.1702431

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Lithium fluoride crystals were exposed to cobalt‐60 gamma radiation at 300° and 78°K. Changes of the flow stress and of the optical absorption were measured in an effort to relate the hardening to identifiable color centers.In crystals irradiated at 300°K there was found to be a good correlation between the flow stress and the concentration ofFcenters. The magnitude of the hardening, however, suggested that it was caused by interstitial defects. Comparison of the hardening produced by additive coloring with that produced by irradiation indicated that the hardening defects were interstitial fluorines. This direct relation between interstitials andFcenters supports a Varley type of mechanism forF‐center production in the bulk crystal. Some limited experiments with NaCl and KCl showed qualitatively the same behavior and suggest that the sameF‐center production mechanism may occur in them.Irradiation of LiF at 78°K produced stable trapped‐hole centers and pulse annealing experiments showed that theVkcenter (self‐trapped hole) contributed to the hardness at low temperatures. A sharp decrease of flow stress was observed at about 110°K where the paramagnetic resonance experiments of Kanzig and the optical measurements of Wiegand and Smoluchowski indicate disappearance of theVkcenter.

ISSN:0021-8979    

DOI:10.1063/1.1702432

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The ferroelectric switching time of barium titanate single crystals has been measured at room temperature as a function of electric field and crystal thickness. The switching time was found to be independent of crystal thickness at high fields in disagreement with earlier work by Merz, who found the switching time proportional to thickness at the same high fields. At low fields the results are in substantial agreement with Merz and other previous work. At fieldsEgreater than a threshold field of 1.4 (1+0.007 cm/d) kV/cm, wheredis the crystal thickness, the switching timetsis given by 9E−1.4±0.1(kV/cm)1.4sec. Below this threshold the switching time is adequately represented byts=0.8 exp[3.5(1+0.007 cm/d) kV/cm/E] &mgr;sec ford≳0.007 cm, but ford«.007 cm, the data are fitted better byts=1.5×103(Ed)−10.3±0.5sec (V)10.3. Thus the data do not agree with the predictions of any known surface layer model of BaTiO3switching.

ISSN:0021-8979    

DOI:10.1063/1.1702433

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

When the inter‐electrode spacing is very small in an alkali‐metal vapor diode, plasma heat transfer cannot be neglected. An efficiency analysis very similar to that of Schock includes this effect and compares it to that due to radiation loss. In the analysis the heat‐transfer coefficienth[W/(cm)2(°K)] is given values 0, 0.005, and 0.01. This range is based on the experimental values ofhobtained in potassium and cesium diodes. The greatest effect ofhon efficiency is found theoretically to occur when the electron‐emitter work function or output voltage is larger than the optimum value for a particular temperature.

ISSN:0021-8979    

DOI:10.1063/1.1702434

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Amplitude dependent internal friction measurements have been made on MgO crystals over the temperature range 0° to 300°C at frequencies of ∼5 cps. Analysis of the temperature dependency of the critical breakaway strain, delineating the transition from amplitude independent to amplitude dependent internal friction, permits an evaluation of the relative pinning strengths of the Fe2+and Fe3+ions, determined on specimens from bulk sources. The Fe3+ion exhibits a binding energy of 0.035 eV, whereas the Fe2+ion has either a lower binding energy and/or a lower mobility which precludes the development of an equilibrium atmosphere. Optical absorption measurements confirm the presence of the Fe3+ion in one bulk crystal and its absence in the other.

ISSN:0021-8979    

DOI:10.1063/1.1702435

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

In previous work we described the fabrication of cold‐worked niobium plus 25% zirconium wire and the use of such wire to construct a solenoid in which a field of 58±1 kG was achieved under loss‐free superconducting conditions. We have continued these experiments with other compositions and find that the critical current in short samples at 21 000 G and 4.2°K decreases with increasing zirconium content for the compositions investigated, namely, Nb+25% Zr, Nb+33% Zr, and Nb+50% Zr. Kunzler observed that the magnetic field required to destroy the supercurrent in these alloys increased with increasing zirconium concentration in the same range of compositions. This behavior led us to build a new solenoid composed of several concentric sections with the lowest composition (25% Zr) on the outside and the highest composition (50% Zr) on the inside. Experiments with this coil are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1702436

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A theory is derived for impurity‐controlled dislocation mobility and the resultant temperature variation of the flow stress of lithium fluoride. The theory is suitable to crystals in which the hardening is primarily due to tetragonal lattice distortions such as result from the introduction of magnesium into lithium fluoride, these being defects whose interactions with dislocations have been calculated previously. Dislocation motion is envisioned as a series of thermally activated dislocation jumps through the stress fields produced by individual solute atoms. The theory predicts the observed temperature variation of the flow stress within 25%, approximate values of the slopes of the velocity‐stress relations, and the activation energy for dislocation motion.

ISSN:0021-8979    

DOI:10.1063/1.1702437

出版商:AIP    

年代:1962

数据来源: AIP