Showing papers in "Journal of Applied Physics in 1959"
TL;DR: In this paper, the authors measured the velocities of individual dislocations in LiF, covering a range of twelve orders of magnitude in velocity, from 10−7 cm/sec to 105cm/sec.
Abstract: Velocities of individual dislocations have been measured in LiF, covering a range of twelve orders of magnitude in velocity, from 10−7 cm/sec to 105 cm/sec. The velocity is extremely sensitive to applied stress at low velocities, and for each crystal there exists a minimum stress for dislocation motion, below which dislocations do not move. The edge components of dislocation loops move considerably faster than the screw components. The upper limit for dislocation velocity appears to be the velocity of sound in the crystal. The effects of temperature, impurities, and radiation damage on dislocation velocity are described. These variables affect the dynamic resistance to motion encountered by a moving glide dislocation.The growth of total dislocation density, the growth of individual glide bands, and the distribution of glide dislocations during plastic deformation are described.The yield stress of LiF is determined by the resistance to motion encountered by a glide dislocation in moving through an otherwis...
1,345 citations
TL;DR: In this paper, the driving force leading to densification during sintering in the presence of a liquid phase and the material transport phenomena have been analyzed and relationships for the densification rate during the rearrangement process, the solution-precipitation process, and the final coalescence process have been determined.
Abstract: The driving force leading to densification during sintering in the presence of a liquid phase and the material transport phenomena have been analyzed and relationships for the densification rate during the rearrangement process, the solution-precipitation process, and the final coalescence process have been determined. These relationships allow an experimental determination of the mechanism of sintering in the presence of a liquid phase on the basis of the time, particle size and temperature dependence of the densification rate. In addition, they allow direct calculations of densification rates to be made for certain simple systems for which property data are available.
918 citations
TL;DR: In this article, a general solution is obtained for the combined action of the transport processes of viscous flow, evaporation-condensation (in a closed system), volume diffusion, and surface diffusion.
Abstract: The relaxation of a nearly plane surface to flatness is discussed under the assumption that all surface properties are independent of orientation. A general solution is obtained for the combined action of the transport processes of viscous flow, evaporation‐condensation (in a closed system), volume diffusion, and surface diffusion. Green's function solutions are developed for each of the transport processes separately, and criteria are obtained to decide which process dominates. The initial forms of these solutions represent point concentrations (particles), or line concentrations (wires) of material set upon an infinite plane. The progressive topographical developments described by the formulas are idealized representations of the latter stages of the sintering of small wires and particles to a plane.
784 citations
TL;DR: In this paper, the effect of a steady axial magnetic field is considered, but motion of heavy ions and electron temperature effects are neglected, and the properties of these space charge waves have been investigated by regarding the plasma as a dielectric and solving the resulting field equations.
Abstract: When a plasma is of finite transverse cross section, space-charge waves may propagate even in the absence of a drift motion or thermal velocities of the plasma. Some of the properties of these space charge waves have been investigated by regarding the plasma as a dielectric and solving the resulting field equations. The effect of a steady axial magnetic field is considered, but motion of heavy ions and electron temperature effects are neglected. Waves are found to exist at frequencies low compared with the plasma frequency as well as waves with oppositely directed phase and group velocities (backward waves).Many of the features of these waves have been verified experimentally by measuring phase velocity and attenuation of waves along the positive column of a low pressure mercury arc in an axial magnetic field. Measurements of electron density have been made using these waves and the results are compared with those obtained by other methods. An interesting feature of these measurements, of value in plasma diagnostics, is that they can be made with frequencies which are small compared with the plasma frequency.
756 citations
TL;DR: In this article, the alternating gradient focusing was applied to a confined region of space by means of alternating and static electric fields, where the motion was governed by Mathieu's equation.
Abstract: Electrically charged iron and aluminum particles having diameters of a few microns have been contained in a confined region of space by means of alternating and static electric fields. The theory is essentially that of alternating gradient focusing; here the motion is governed by Mathieu's equation. Under certain circumstances when many particles are confined the three dimensional focusing force and the Coulomb repulsion results in a ``crystaline'' array which can be ``melted'' and reformed.
577 citations
TL;DR: A survey of spherulites formed by the isothermal crystallization of polypropylene from the melt in the temperature range 110°−148°C is given in this paper. But their structural morphology, optical properties, melting behavior, and growth rates have not been examined.
Abstract: A survey has been made of spherulites formed by the isothermal crystallization of polypropylene from the melt in the temperature range 110°–148°C. Four types of spherulite have been distinguished and their structural morphology, optical properties, melting behavior, and growth rates have been examined.
571 citations
TL;DR: In this article, a method for measuring the resistivity of metallic specimens is described, which is made by noting the rate of decay of flux from a bar situated in an external magnetic field that has been rapidly reduce to zero.
Abstract: A method for measuring the resistivity of metallic specimens is described. The measurement is made by noting the rate of decay of flux from a bar situated in an external magnetic field that has been rapidly reduce to zero. The method is suitable for specimens greater than 5×10−3 cm in diameter. For a specimen 1 cm in diameter, resistivities from 10−11 to 10−3 ohm‐cm may be measured with an error of less than three percent. The method requires no contact to the specimen, and local values of resistivity may be measured. Several applications are described.
340 citations
TL;DR: In this article, a representative crystal with about 500 dislocations per cm2 is examined in detail to provide general information about their distribution and sources of dislocation which are important at particular stages of growth are isolated and means to minimize or eliminate them.
Abstract: The dislocations which occur in silicon crystals grown by the Czochralski method with and without a crucible are studied by etching and copper decoration techniques. A representative crystal with about 500 dislocations per cm2 is examined in detail to provide general information about their distribution. Sources of dislocations which are important at particular stages of growth are isolated and means found to minimize or eliminate them. The sources include generation by thermal shock from surface damage or residual dislocations in the seed; poor epitaxy at the seed; plastic generation in the bulk of the crystal; effects of segregation of impurities. Plastic generation is the only source found in the bulk of a crystal. ``Spontaneous'' formation of dislocations from excess vacancies is not found. Impurity segregation causes some generation at the tip end of crystals. For certain crystallographic directions it is possible to eliminate residual dislocations and thenceforth grow a dislocation‐free crystal. This is interpreted in terms of climb. In a super‐saturation of vacancies, an edge dislocation can be forced completely out of a crystal; a screw will remain straight or may be distorted into a coaxial helix. By growth along 〈100〉 or 〈111〉 axes under conditions which favor a vacancy supersaturation, screw as well as edge and mixed dislocations can propagate to the surface and be eliminated. The observations are consistent with this interpretation. When the dislocations are eliminated, the growing crystal can withstand large temperature fluctuations without further generation of dislocations. A procedure is outlined for the growth of dislocation‐free silicon crystals. Germanium crystals free of dislocations have been grown by a direct application of the method. It is believed that the conclusions reached during the course of this investigation may be applied to the development of methods for growing dislocation‐free crystals of other substances.
321 citations
TL;DR: In this paper, the kinetic theory for the rate of stress-assisted precipitation on dislocations is re-examined in order to extend the work of Cottrell and Bilby.
Abstract: The kinetic theory for the rate of stress‐assisted precipitation on dislocations is re‐examined in order to extend the work of Cottrell and Bilby. Two approximate expressions are used for the elastic interaction between a solute atom and edge and screw dislocations: V=−A sinθ/r and V=−B/r, respectively. The resulting partial differential diffusion equations are integrated numerically to get the time‐dependent rate of precipitation on an isolated dislocation. These results are used to calculate the short‐time part of the precipitation curve for an array of dislocations. Exact steady‐state solutions to the diffusion equations are derived for both interactions and are used with a variational procedure to establish the long‐time part of the curve for a regular array. For very short times the precipitated fraction W is proportional to t⅔ as derived by Cottrell and Bilby, but this result is not accurate over the range of t during which most of the precipitation occurs. The long‐time part of the curve is given a...
308 citations
TL;DR: In this article, the anomalous behavior of the group VA metals can be accommodated within the framework of Snoek's model by taking account of the specific nature of solid solutions based on these metals.
Abstract: Mechanical relaxation measurements are used extensively to obtain information on the diffusion rate of interstitial solute atoms in body‐centered cubic metals. Such studies have been stimulated by a model, developed by J. L. Snoek, which yielded a relationship between a relaxation time, an experimental parameter, and the diffusion coefficient of the solute atom. Although Snoek's model was confirmed very well for solid solutions of carbon or nitrogen in α‐iron, a number of anomalies were observed when relaxation studies were extended to the group V transition metals.An extensive experimental study has been made of the factors that influence relaxation times. The anomalous behavior of the group VA metals can be accommodated within the framework of Snoek's model by taking account of the specific nature of solid solutions based on these metals.Diffusion data obtained by a variety of relaxation techniques are presented for oxygen, nitrogen, and carbon in vanadium, niobium (columbium), and tantalum. These data ...
301 citations
TL;DR: In this paper, the authors measured the amount of 90° reorientation during poling from mechanical strains measured during the poling process and showed that very high compressive stress parallel to the polar axis causes 90° switching of nearly all aligned domains, and, therefore, removes virtually all polarization.
Abstract: The amount of 90° reorientation during poling was determined from mechanical strains measured during the poling process. With tetragonal lead titanate zirconate 53% of the possible 90° reorientation occurred during poling, but this figure dropped to 44% upon removal of the poling field. With barium titanate the figures are only 17% and 12%, respectively. Comparison of the polarization of poled polycrystalline barium titanate with that for single crystals indicates that 180° reorientation is virtually perfect. Application of very high compressive stress parallel to the polar axis causes 90° switching of nearly all aligned domains, and, therefore, removes virtually all polarization. Curves of released charge as function of mechanical strain are nearly linear, but curves of released charge as function of stress are strongly nonlinear. Application of high compressive stress perpendicular to the polar axis also causes 90° domain reorientation and a reduction in the total polarization of the ceramic. This domai...
TL;DR: In this paper, a theory of pressure buildup under unipolar ion conduction is presented and verified experimentally, showing that constriction of the current flow leads to sizeable pressures in insulating liquids.
Abstract: A theory of pressure buildup under unipolar ion conduction is presented and verified experimentally. Constriction of the current flow leads to sizeable pressures in insulating liquids.
TL;DR: In this paper, an attempt is made to account for the observed birefringence of the various types of polypropylene spherulite in terms of preferred crystalline orientation.
Abstract: An attempt is made to account for the observed birefringence of the various types of polypropylene spherulite in terms of preferred crystalline orientation. Evidence is also presented showing that some of these spherulites crystallize with a new metastable crystal structure, not previously described.
TL;DR: In this article, the width and depth of the potential wells surrounding disordered regions in neutron irradiated n-type germanium and extrinsic silicon are estimated for a wide range of sample characteristics, e.g., scattering of conduction electrons, absorption of holes and polarizability.
Abstract: The width and depth of the potential wells surrounding disordered regions in neutron irradiated n‐type germanium and extrinsic silicon are estimated. Numerical examples of well dimensions for a wide range of sample characteristics are presented. Some effects of disordered regions, e.g., (a) scattering of conduction electrons, (b) absorption of holes, and (c) polarizability, are discussed.
TL;DR: The photoelastic constants and their dispersion for visible light were determined for two samples of vitreous silica, Corning and Herasil No. 1, and the results for the mercury green line, 546 mμ, are quoted here as mentioned in this paper.
Abstract: The photoelastic constants and their dispersion for visible light were determined for two samples of vitreous silica, Corning and Herasil No. 1. The results for the mercury green line, 546 mμ, are quoted here. The photoelastic constants were 4.22×10−13 (d/cm2)−1 (ordinary ray) and 3.56×10−13 (d/cm2)−1 (extraordinary ray). From the ratio of Poisson's ratio to Young's modulus 0.216×10−12 (d/cm2)−1 and Young's modulus 0.76×1012 (d/cm2), which were also determined, there were calculated the pressure coefficient of refractive index 0.909×10−12 (d/cm2)−1 and the elasticity volume coefficient of refractive index V dN/dV=0.34. Comparison of these results with those reported for other glasses indicates that the oxygen ions of vitreous silica are more deformable then the oxygen ions of other siliceous glasses. In vitreous silica about ⅓ of the volume change accompanying an elastic dilatation arises from the dilatation of the oxygen ions. A comparison is also made with the results reported for corresponding thermally induced effects. It indicates that (a) during a thermal dilatation of a siliceous glass, the oxygen ion undergoes a dilatation which in the case of most siliceous glasses causes an equivalent dilatation of the body, but which in the case of vitreous occurs internally instead, and (b) in crystal quartz no appreciable dilatation of the oxygen ion occurs during a thermal dilatation. The thermal dilatation of the oxygen ion in the glasses would thus seem related to its strained bond configuration.
TL;DR: The distribution of imperfections within the interior of crystals has been studied using ''projection topographs'' which are x-ray diffraction images showing a projection of a slice of crystal and the imperfections in it as mentioned in this paper.
Abstract: The distribution of imperfections within the interior of crystals has been studied using ``projection topographs'' which are x‐ray diffraction images showing a projection of a slice of crystal and the imperfections in it Individual dislocations have been observed in single crystals of diamond, silicon, germanium, lithium fluoride, sodium chloride, silver chloride, magnesium oxide, calcite, quartz, and aluminum From the variation of dislocation contrast with the orientation of the x‐ray reflecting plane the direction of Burgers vector can be found Dislocations can be seen with good contrast when the product of linear absorption coefficient μ and slice thickness t is of the order of unity or less If μt≫1 the contrast is reversed through the Borrmann effect Stereo pairs of projection topographs can be prepared from the pair of reflections hkl and hkl
TL;DR: In this paper, the anisotropy and magnetostriction of single crystals of several ferromagnetic materials have been determined experimentally, including the metals iron and nickel, binary alloys of nickel iron, silicon iron, aluminum iron, cobalt nickel, and cobalt iron.
Abstract: The anisotropy and magnetostriction of single crystals of several ferromagnetic materials have been determined experimentally. The materials include the metals iron and nickel, binary alloys of nickel iron, silicon iron, aluminum iron, cobalt nickel, and cobalt iron, ternary alloys of molybdenum nickel iron, nickel cobalt iron, and molybdenum aluminum iron, and magnetite. The effect of the order‐disorder reaction on these properties was measured for several of the alloys.The present data for the nickel iron and silicon iron systems agree well with recently published values. Ordering generally raises the magnetostriction and lowers the anisotropy of the aluminum iron alloys near the Fe3Al composition. The first anisotropy constant, K1, for the cobalt nickel system as derived from torque curves is similar to old data derived from magnetization curves. However, K1 for cobalt iron (30, 35, and 45% cobalt) appears to be considerably larger than previously reported. In general, the addition of cobalt to nickel ...
TL;DR: In this article, a statistical approach is used to determine the effect of porosity in ceramic materials on their dielectric breakdown strength, which is in good agreement with the experimental data for lead zirconate titanate ceramics.
Abstract: A statistical approach is used to determine the effect of porosity in ceramic materials on their dielectric breakdown strength. The calculated drop in dielectric strength is in good agreement with the experimental data for lead zirconate titanate ceramics. The theory shows that the measured dielectric strength in porous materials is a function of the porosity, the void size, and of the dimensions of the test sample.
TL;DR: In this article, experimental measurements of the densification rate and microstructure changes taking place during sintering of the iron-copper system, which is typical of those systems showing spheroidal grain development, indicate that in this system the rate of densification during liquid phase Sintering is controlled by diffusion through a liquid film between particles.
Abstract: Experimental measurements of the densification rate and microstructure changes taking place during sintering of the iron‐copper system, which is typical of those systems showing spheroidal grain development, indicate that in this system the rate of densification during liquid phase sintering is controlled by diffusion through a liquid film between particles. Dependence of the sintering rate on time, particle size and temperature are in agreement with theoretical predictions. A theoretical estimation of the sintering rate is in good agreement with experimental measurements.
TL;DR: In this article, a special technique for the accurate measurement of thermal conductivity is discussed, which involves use of the Peltier heat to maintain a temperature gradient along the specimen.
Abstract: A special technique for the accurate measurement of thermal conductivity is discussed. The method involves use of the Peltier heat to maintain a temperature gradient along the specimen. Straightforward measurements allow calculation of the absolute value of the thermoelectric power, thermal conductivity, and electrical resistivity. An especially useful feature of the method is that the thermoelectric figure of merit is given in terms of the ratio of two voltages. The theory is presented for the case in which the radiative heat transfer is important. The method has been tested experimentally at 300°K only, but analysis suggests that accurate measurements of thermal conductivity can be made by this technique on low thermal conductivity materials of small dimensions up to 1000°K.
TL;DR: In this paper, a new formula has been derived by adaptation of a method of Kramers to angular coordinates and to a gyroscopic equation of motion, which gives for the mean rate of transition between orientations a formula of the form v
Abstract: Weil and others have used the temperature variation of remanence and a formula of Neel's to determine volume‐distribution curves for a powder of single‐domain particles. The basic principle is that the time constant for spontaneous reversal of the magnetization, through thermal agitation, is effectively infinite for particle volume v>vc and zero for v
TL;DR: In this article, two x-ray methods have been developed for determining the crystallinity of cellulose using a Geiger counter spectrometer and two methods were applied to six native cotton varieties, to a cross-bred variety, and to two cottons chemically modified with ethylamine.
Abstract: Two x‐ray methods have been developed for determining the crystallinity of cellulose using a Geiger counter spectrometer The two methods were applied to six native cotton varieties, to a cross‐bred variety, and to two cottons chemically modified with ethylamine The x‐ray scattering curves for each of the nine samples were compared with those from a highly crystalline sample, a cotton hydrolyzed in HCl, and an amorphous cotton sample to provide a relative measure of crystallinity, or crystalline indexWith fully corrected data the average crystalline index of the six cotton varieties was found to be 683 and 787% by the correlation and by integral methods, respectively The crystalline indices of the remaining samples determined by the correlation and by the integral methods are, respectively, cross‐bred cotton (S×P), 543 and 772%; cotton treated with anhydrous ethylamine, 297 and 509%; and cotton treated with 75% aqueous ethylamine, 283 and 503%
TL;DR: In this paper, the concept of octahedral site preference energy in spinels has been extended to include Madelung and short-ranged as well as crystal field terms, and a set of site preference energies is formulated which can be used to predict the ionic distribution of spinels involving the nontransition and the transition ions.
Abstract: The concept of octahedral site preference energy in spinels has been extended to include Madelung and short‐ranged as well as crystal field terms. A set of site preference energies is formulated which can be used to predict the ionic distribution of spinels involving the nontransition as well as the transition ions. The agreement between predicted and experimentally determined ionic distributions is surprisingly good, and a number of heretofore puzzling distributions are explained.
TL;DR: In this article, the properties and characteristics of a glow discharge to a nearly spherical hollow cathode were investigated and it was shown that current densities in excess of 0.5 amp/cm2 can be drawn from the cathode with negligible deterioration from sputtering.
Abstract: An experimental study has been made of the properties and characteristics of a glow discharge to a nearly spherical hollow cathode. Current densities in excess of 0.5 amp/cm2 can be drawn from the cathode with negligible deterioration from sputtering. In neon, the discharge exhibits a stable and reproducible negative volt‐ampere characteristic at currents of a few milliamperes. At these currents, probe measurements indicate the plasma in the hollow contains ∼1‐v electrons in concentrations greater than 1013/cm3.
TL;DR: In this paper, three principal effects have been identified as contributing to this anisotropy, namely, formation of directed Fe pairs in the Ni matrix, an effect due to the angle-of-incidence between the substrate and the depositing beam, and anisotropic stress in combination with the isotropic magnetostriction.
Abstract: Evaporated films of Permalloy are found to be uniaxially anisotropic under all the conditions of preparation studied so far, including deposition in dc, zero, and rotating‐circular magnetic fields. Three principal effects have been identified as contributing to this anisotropy, namely; (1) the formation of directed Fe pairs in the Ni matrix, (2) an effect due to the angle‐of‐incidence between the substrate and the depositing beam, and (3) anisotropic stress in combination with the isotropic magnetostriction. The evidence for directed pairs comes from the compositional dependence of the anisotropy; the angle‐of‐incidence effect is demonstrated by depositing onto tilted substrates; anisotropic stress effects are shown by detaching the film from the substrate. The simultaneous presence and interaction of the above effects is thought to be the reason for the variability in the anisotropy which is encountered in Permalloy films.
TL;DR: In this paper, the spin resonance behavior in room temperature irradiated n-type silicon is observed to be significantly different for silicon grown in quartz crucibles from that grown by the floating zone method.
Abstract: The spin resonance behavior in room temperature irradiated n‐type silicon is observed to be significantly different for silicon grown in quartz crucibles from that grown by the floating zone method. The dominant spectrum in each is discussed. The defects giving rise to the spectra are interpreted as containing impurity atoms and as having formed when the impurities trap mobile interstitials and/or vacancies. In quartz crucible grown silicon, the impurity may be oxygen. In the floating zone material, the impurity appears to be the phosphorus used in the doping. A 20°K irradiation and anneal is described which suggests the temperatures at which this defect motion is occurring. Features of the spin resonance spectra suggest that the vacancy may be the mobile effect.
TL;DR: In this article, the effects of irradiation on the infrared absorption and photoconductivity in silicon are reported, and the significance of these results is discussed in Section 2.1.
Abstract: The effects of irradiation on the infrared absorption and photoconductivity in silicon are reported. The absorption near the intrinsic edge is increased and drops off more gradually toward longer wavelengths. Several absorption bands are introduced by neutron irradiation with peak absorptions at 1.8, 3.3, 3.9, 5.5, and 6.0 μ, respectively. The observation of each band depends upon the position of the Fermi level. The 1.8‐μ band has also been studied for deuteron irradiated and electron irradiated silicon, and the 3.3‐μ band has been observed in electron irradiated samples. The absorption bands arise from electronic excitations of various types of defects and associated photoconductivity has been observed for the 3.9‐μ and 5.5‐μ bands. In addition absorption bands have been observed at long wavelengths: 20.5, 27.0, and 30.1 μ, which are associated with lattice vibration. The significance of these results is discussed.
TL;DR: In this article, the authors investigated the space-charge-limited electrical behavior of a trap-free insulator containing both mobile electrons and holes under the approximation of neglecting diffusion current when both contacts are ohmic.
Abstract: The space‐charge‐limited electrical behavior of a trap‐free insulator containing both mobile electrons and holes is investigated under the approximation of neglecting diffusion current When both contacts are ohmic, the dependence of two‐carrier space‐charge‐limited current on voltage and interelectrode spacing remains the same as in the one‐carrier case; ie, the current varies as the square of the voltage and as the inverse cube of the spacing For given voltage and spacing, however, the two‐carrier current is usually orders of magnitude larger than the one‐carrier current This is in striking contrast to the case of space‐charge‐limited flow of electrons and positive ions in a vacuum The two‐carrier current in an insulator can be reduced to the size of the one‐carrier current either by making one contact highly blocking or by reducing the mobility of one of the carriers to zero While the first approach yields in detail the well‐known one‐carrier case, the second approach differs from the one‐carrier
TL;DR: In this article, shadow micrographs of the spheres before and after sputtering were used to determine the influence of the angle of incidence on sputtering yields of small metal spheres.
Abstract: Small metal spheres are bombarded by uniform Hg+ ion beams of low energy (125 to 800 ev). Comparison of shadow micrographs of the spheres before and after sputtering makes it possible to determine the influence of the angle of incidence on sputtering yields. Fe, Ta, and Mo showed a pronounced increase in yield at more oblique incidence of the ions while Au, Ag, and Pt showed this effect only slightly.