摘要:

Sapphire with 0.11‐wt% titania in solution (mainly as TiO1.5) was aged isothermally in air up to 21 days at 1100°–1600°C. Optical studies showed that the solubility limit of the titania was exceeded at 1400°C in air, and consequently needle‐shaped precipitates were developed. For aging temperature between 1100° and 1300°C, precipitation initiated at grown‐in dislocations and at subboundaries. This phenomenon was attributed to rapid oxidation along these defects. Following this initial stage, precipitates formed uniformly throughout the crystals, and they coarsened with time. The variation of average needle length with time was measured. Knoop microhardness measurements showed that Ti4+ions plus the attendant defects in solution caused measurable hardening of sapphire, but the greatest changes resulted from precipitation. Significant hardening resulted from aging at 1300°C for 13 days. The hardness anisotropy in the basal plane of sapphire, i.e.,KH⟨101¯0⟩>KH⟨112¯0⟩, was not altered by precipitation.

ISSN:0021-8979    

DOI:10.1063/1.1659569

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

We have observed the anomalous longitudinal magnetoresistance conditionsR(H) = 0 and 0<R(H) <R(0) on a [111]‐oriented copper crystal specimen. The magnetoresistance voltages measured by two probe sets on mutually perpendicular faces of the specimen are observed to have a significant difference. Both of these effects are shown to be due to very slight misorientations of the specimen with respect to the magnetic field. In light of the observations, we present some precautions which should be observed in making longitudinal magnetoresistance measurements on high‐purity materials.

ISSN:0021-8979    

DOI:10.1063/1.1659570

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Using radio‐tracer210Pb, the diffusion of lead has been studied in PbTe at 700°C as a function of composition and doping level. The results indicate that the predominant cation defect is of the Frenkel type.

ISSN:0021-8979    

DOI:10.1063/1.1659571

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Three‐dimensional distribution patterns of the strain and dislocations developed around indented areas in germanium crystals are observed as a function of the deformation temperature between 20° and 700°C by use of x‐ray diffraction topography. The size of the deformed region around an indented area is found to have a relationship with the hardness value, i.e., the former begins to increase abruptly at the temperature where the latter begins to decrease abruptly as the deformation temperature is raised. The areas indented at high temperatures are subjected to two kinds of treatments: One group of areas is brought to room temperature after indentation while an indenter load is applied, and the other is cooled after an indenter load has been removed. Rearrangement of dislocations takes place during annealing of specimens. Annealing brings about a configuration of dislocations lying parallel to ⟨110⟩ directions.

ISSN:0021-8979    

DOI:10.1063/1.1659572

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Copper crystals of a cross section 0.5×0.1 cm and of an initial dislocation densityN50–5000 cm/cm3were deformed in tension, and Borrmann x‐ray topographs were taken after successive stress increments. All dislocations were observed and Burgers vectors determined. Stereo pairs were made. The grown‐in dislocations were moved very little by the applied stresses. For crystals of lower initialNmost of the dislocation generation could be related to localized stresses in the grip regions, while in the crystals with higher initialNthe generation probably was related to grown‐in dislocations. Slip bands were formed; neither the source nor the generation mechanism of dislocations in these bands was determined. Screw dislocations were left by edge segments running across the crystal. These screw dislocations cross slipped frequently at stresses of a few grams/mm2, and this process tended to fill the volume of crystal between the bands with dislocations. By counting all new dislocations the shear strain was computed and ``stress‐strain'' curves were obtained.

ISSN:0021-8979    

DOI:10.1063/1.1659573

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An analytical model of the dislocation core is proposed. The center of a crystal dislocation in this model is represented by a continuous distribution of infinitesimal dislocations, whose distribution function incorporates the atomic configurations of dislocations as determined by Cotterill and Doyama using a many‐body‐crystal model of copper. The distribution functions used have the same form as the Peierls model except the width parameter, which is about twice that of the original Peierls model. Using the present model and methods of the continuum theory of dislocations, numerical calculations are made for the interaction energies between two parallel screw and two parallel edge dislocations. The results are significantly different from those predicted by the classical theory when the separation distance is less than ten atomic distances. Approximate expressions for the interaction energy between two coplanar edge dislocations and for that between two coplanar screw dislocations are obtained. The magnitudes of both the interaction energy and interaction force remain finite in the present model, enabling the unique determination of the self‐energies of single dislocations and edge dislocation dipoles. Dislocation splitting in fcc metals is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659574

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The thermally activated release of the dielectric polarization of ZnF2:LiF crystals has been studied using the ionic thermoconductivity method. Measurements of the current discharge are made in single crystal samples oriented for polarization in the [001], [100], and [110] directions in order to study the crystallographic orientation dependence of the dielectric relaxation process. Strong discharge currents are observed only for [001]‐oriented crystals. The important parameters (including the activation energy, relaxation time, and number of dipoles) for the process are determined; the change in dipole orientation causing the discharge is examined in relation to possible anion vacancy movements in the lithium‐doped zinc fluoride crystal structure. The results confirm that the dielectric relaxation of lithium‐doped ZnF2is dependent upon the crystallographic orientation of the dielectric material.

ISSN:0021-8979    

DOI:10.1063/1.1659575

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The ferroelectric tungsten—bronze system KxNa1−xBa2Nb5O15is studied particularly in the regionx=0.7–0.9 where the crystals remain tetragonal down to at least 77°K. These crystals should have many applications in the quantum electronics field. The temperature and wavelength dependence of the two indices of refraction are reported as well as the temperature dependence of the linear electro‐optic constant and the nonlinear optical effect (second‐harmonic generation). These quantities are discussed in terms of a model that treats these ferroelectrics as biased paraelectrics, the biasing field being supplied by the spontaneous polarization. The agreement is fairly good. To demonstrate the usefulness of these materials anx=0.8 crystal was used for the efficient intracavity harmonic generation of 0.53‐&mgr; light using a 1.06 &mgr; Nd&sngbnd;YAG laser. The same crystal was used to phase lock the laser, thus increasing the harmonic power.

ISSN:0021-8979    

DOI:10.1063/1.1659576

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The needle crystals of tungsten oxide grown on the tungsten substrate from vapor phase were studied by field emission and electron microscopy. The observed FEM patterns of the needles were quite similar to the pattern of the oxidized W emitter and mostly had twofold symmetry. Less frequently, the FEM patterns having nearly threefold and fourfold symmetries could be observed. From the comparison of the electron micrographs as well as the FEM patterns of a needle and an oxidized W emitter, evidence was obtained that the surface of the oxidized emitter tip had been covered with thin layer of a crystallized tungsten oxide.

ISSN:0021-8979    

DOI:10.1063/1.1659577

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An analysis is presented of the forced oscillations of a gas‐filled bubble at rest in a large body of a linear viscoelastic fluid. Two types of forcing are considered. In the first, oscillations are induced by a pressure surge on the system. For the three‐parameter fluid model employed, numerical computations show that for a given ratio of the fluid's elastic modulus to the pressure surge, the damping of the bubble motion exhibits a maximum as a function of the fluid relaxation time at a value of this parameter equal approximately to one‐fifth the natural period of oscillation. At very high or very low relaxation times, the damping becomes insignificant. As the second type of forced oscillation, we consider the motion induced by the application of ultrasonic waves to the system. Here, damping is found to depend strongly on the product of impressed frequency and fluid relaxation time.

ISSN:0021-8979    

DOI:10.1063/1.1659578

出版商:AIP    

年代:1971

数据来源: AIP