摘要:

Determination of acoustic phase velocity in liquid or solid specimens using standing‐wave (i.e., continuous wave) ultrasonic techniques requires the use of a transducer correction formula. Previous approximations for the transducer correction in the case of a one‐dimensional (planar) composite resonator are considered explicitly and their accuracy and range of validity are quantitatively examined. An improved transducer correction formula is derived which is shown to be substantially more accurate than previous approximations. Quantitative evaluation of the accuracy of this improved transducer correction is presented for simulated velocity measurements in a typical liquid and a typical solid specimen.

ISSN:0021-8979    

DOI:10.1063/1.1663281

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Bursts of electroluminescence were produced when a 50–500‐ns excess voltage pulse was superimposed on the ``drive'' voltage which produced an acoustoelectric domain. The intensity of the luminescence was found to increase with the amplitude of the excess voltage and first increase then decrease as a function of the drive voltage. Self‐illuminated photographs of the domains showed them to be ≈0.4 mm wide.

ISSN:0021-8979    

DOI:10.1063/1.1663282

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Two independent reports in the literature for the elastic constants of zircon (zirconium silicate) are in disagreement by an order of magnitude and are reported without specifying the conditions of the mineralogical specimens. However, natural zircon crystals frequently contain uranium and thorium atoms as an impurity so that zircon can exist in a metamict (radiation damaged) condition. A redetermination of the elastic constants has been carried out on small synthetic crystals and on high‐purity natural single crystals of nonmetamict zircon of lattice parametersao= 6.606(2) Å,co= 5.980(2) Å by ultrasonic pulse superposition and also by phase comparison methods. The values in 1012dyn/cm2arec11= 4.237,c33= 4.900,c44= 1.136,c66= 0.485,c12= 0.703, andc13= 1.495. The estimated uncertainty in the measurements are 0.4% forc11,c33,c44, andc66, and 3% forc12andc13. Wave velocity measurements have also been carried out on a metamict zircon crystal (density 4.531 g/cm3) and it is shown that the velocities are reduced by about one‐fifth the normal values. The compressibility coefficients calculated from the new elastic constants data differ from those determined by diffraction data, though this may be part of a general discrepancy between such measurements.

ISSN:0021-8979    

DOI:10.1063/1.1663283

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Two types of ambiguity concerning indexing of electron diffraction patterns have been cleared up by making use of the Kikuchi lines. A convenient unambiguous method of uniquely indexing patterns is suggested assuming the beam is always along the viewing direction no matter how the picture is printed. It is shown that there are two completely equivalent ways of indexing the Kikuchi pattern, e.g., [111] or [1¯1¯1¯]. The method is also useful in interpreting dark‐field pictures when top‐bottom contrast is concerned.

ISSN:0021-8979    

DOI:10.1063/1.1663284

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The specific heats of ZnTe, ZnSe, and GaP have been measured to ±3% in the temperature region from 15 to 150°K. The experimental results agree, within the experimental error, with the available previous measurements. The measurements were performed primarily to obtain values of the specific heat for comparison with values calculated from a lattice dynamics model. The parameters used in the theoretical model were determined from second‐order Raman spectra. The comparison thus provides a test of the reliability of acoustic‐phonon dispersion curves obtained from second‐order Raman spectra.

ISSN:0021-8979    

DOI:10.1063/1.1663285

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The concept of special grain boundary dislocations (as distinct from crystal dislocations) has been used to study the mechanism of the passage of crystal dislocations through tilt boundaries in the simple cubic and bcc systems. It is shown that the Burgers vector of a grain boundary dislocation is not arbitrary but should be a vector belonging to a restricted set defined in terms of the translation vectors of the two grains separated by the grain boundary. It is next shown that a grain boundary dislocation can be constructed in a bicrystal in the same manner as a crystal dislocation in a single crystal. The properties of these dislocations in a bicrystal are studied. It is shown that a crystal dislocation can pass through a tilt boundary without altering its over‐all structure by first dissociating into partials whose Burgers vectors are integral units of those of the grain boundary dislocations defined for the bicrystal. The principles involved are illustrated by means of an example each in the simple cubic and bcc systems.

ISSN:0021-8979    

DOI:10.1063/1.1663286

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Because of the polarization by the electromagnetic field, the grains of very thin metallic films spread over an amorphous substratum are under bipolar interaction forces. One of them,F0, is created by the field due to the electromagnetic oscillations at zero temperature. Another one,FT, is due to the field maintaining the radiation of the thermodynamic equilibrium. A third one,FE, is superimposed onto the first ones,F0andFT, at the time of illumination of the films by the evaporating cell or by an auxiliary source.F0,FT, andFEare expressed with the same function &phgr;(&ohgr;) depending upon not only the permittivity &egr;gof the grains and the permittivity &egr;sof the substratum but also on the shape of the grains, their distances, and their dimensions. The last two modify &egr;g, which is very different from &egr;∞in the bulk metal. &phgr;(&ohgr;) shows a first maximum which is dependent upon geometrical data, located in the infrared or the visible. Its amplitude is limited only by the imaginary part ofF0. However, the main part ofF0is concentrated in the far ultraviolet. Nevertheless, an intense illumination in the first‐maximum spectral interval can superimpose a nonnegligible forceFEontoF0andFT. The relative magnitude of these forces can be discussed in the case of granular films of silver on carbon. The fact is that structural modification can be obtained by illumination of these films when they are maintained under ultravacuum until 21 h after their formation.

ISSN:0021-8979    

DOI:10.1063/1.1663287

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Consideration is given to the image formed in the electron microscope of two crystals stacked one above the other when these show a relative rotation about an axis perpendicular to the electron beam. Dark‐field moire´ fringe patterns are predicted when certain conditions relating to the relative proximity to the Bragg condition of the two crystals are fulfilled. The limits of these conditions and the spacings of the fringes are formulated in terms of the angle of tilt and the direction of the tilt axis.

ISSN:0021-8979    

DOI:10.1063/1.1663288

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Fine particles of Zn, Mn, and Se are produced in a flowing system of argon gas. The experimental geometry is described, and the effect of experimental parameters (metal vapor pressure, gas flow rate, and oxidants) is characterized. These particles are studied using a transmission electron microscope in both imaging and electron diffraction modes. Mn and Zn formed well‐defined crystals as verified by electron diffraction, while Se did not. Even small amounts of oxygen inhibited the proper crystal growth.

ISSN:0021-8979    

DOI:10.1063/1.1663289

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Homogeneous nucleation of small Zn particles has been observed in a flowing inert‐gas system. Zn vapor was produced by heating the bulk metal near 700 K in flowing N2at pressures near 15 Torr. Nucleation of small Zn particles took place in a cooler region downstream from the furnace. Cooling occurred by gas conduction to room‐temperature walls. Particle sizes measured by electron microscopy were from 5 to 5000 nm. Samples were obtained with varying metal temperature, gas flow rate, pressure, and position in the collection chamber. Particles grew with time and had a predominant shape characterized as a regular hexagonal prism.

ISSN:0021-8979    

DOI:10.1063/1.1663290

出版商:AIP    

年代:1974

数据来源: AIP