摘要:

The effect of various electromagnetic boundary conditions on the propagation of surface waves in piezo‐electrics is considered. Basic for the analysis is the introduction of an electric ``surface impedance'' which relates the electric potential to the normal component of electric displacement in the surface. An analytic expression for this impedance is found in the case of weak piezoelectric coupling which permits the calculation of the phase velocity for arbitrary values of the impedance. It is also shown that within the weak coupling approximation the surface impedance contains the information on material parameters necessary for calculating the power transferred to surface waves from an impressed electric current.

ISSN:0021-8979    

DOI:10.1063/1.1658060

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The acoustic attenuation of shear and longitudinal waves propagating along thecaxis in LiTaO3has been measured from 1 to 9 GHz. Measurements were made from 4° to 300°K using the microwave pulse‐echo technique and at 300°K using optical Bragg diffraction. The shear‐ and longitudinal‐wave attenuation in LiTaO3at 300°K was found to be similar to that of LiNbO3. However, the change in shear‐wave attenuation between 4° and 300°K is much smaller in LiTaO3than in LiNbO3.

ISSN:0021-8979    

DOI:10.1063/1.1658061

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The narrow beam attenuation coefficient of air was measured at 5.895 keV. An55Fe source of Mn x rays with a CrK&bgr;filter and a collimated low‐energy sodium iodide counter were used. The photon intensity as a function of the source‐detector distance was determined in vacuum and in atmospheric air. The value of the measured coefficient is 24.55±0.25 cm2/g.

ISSN:0021-8979    

DOI:10.1063/1.1658062

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Observations on the cusp‐shaped ``cracks'' which form around crystals growing in gels are reported. It is shown that the cusps are interconnected, that the most common shape of the cusps is three‐sided, that the cusp sides have a ridged structure, and finally, that the disposition of cusps around a growing crystal often displays a good deal of symmetry. It is concluded that the crystal is completely surrounded by liquid as it grows, and that this liquid is contained within a womb‐like enclosure formed by the cusps surrounding a crystal. It is proposed that the surface of the womb made of the gel cusps acts like a membrane, and additional nutrients enter the womb through osmosis.

ISSN:0021-8979    

DOI:10.1063/1.1658063

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

&agr;‐Iron whiskers were grown under observationin situin an electron microscope by the thermal decomposition of iron carbonyl in a stream of hydrogen at 710°–820°C. As many as three growth periods with distinct growth rates were observed. An initial slow growth was postulated to be due to growth at the base, caused by localized stresses in the three‐dimensional iron deposit on the screen on which the whiskers were growing. Subsequent growth at the tip appeared to be limited by both the impingement rate of iron carbonyl and the surface flux of iron on the shaft of the whisker. The diffusion coefficient, calculated to account for the observed maximum growth rate, is in good agreement with the value given in the literature. Subsequent slower growth was accounted for by the incorporation of the iron contained in the Fe (CO)5which impinged on the tip alone. The morphological features observed and interpreted were tilting, bridge growth, lateral growth, curving, kinking, junction formation, and neck formation. It was shown that a whisker may grow by plastic deformation under tensile stress and simultaneous deposition on its shaft from a supersaturated gaseous atmosphere.

ISSN:0021-8979    

DOI:10.1063/1.1658064

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The Curie temperatures and the electrical resistivity at 4.2°, 78°, and 300°K have been measured for nickel‐carbon solid solutions containing up to 1.5 at.% carbon. The resistivity at 4.2°K increases at the rate 3.48±0.06 &mgr;&OHgr; cm/at.% carbon; whereas the Curie temperature decreases by ∼30 C°/at.% carbon. The electrical resistivity shows positive apparent deviations from Matthiessen's rule. The variation of the Curie temperature is consistent with donor theories in which carbon donates both itspelectrons to thedband of the metal. The susceptibility shows an unusually large field dependence near the Curie temperature presumably because of as yet unclassified modifications of the nickel moment due to the presence of carbon.

ISSN:0021-8979    

DOI:10.1063/1.1658065

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

``Particle'' or domain sizes and angular misorientations between domains change during the annealing of cold‐worked crystals, leading to primary and secondary extinction changes in the x‐ray diffraction lines. It has been found that domain sizes are too small in cold‐rolled copper to produce significant primary extinction. An attempt was made to avaluate the secondary extinction changes in terms of Darwin's equation. The invalidity of the commonly used form of this equation was shown. With a dislocation model for the substructure it was possible to evaluate the integrated intensity ratioI/Is, with‐to‐without extinction, in terms of domain sizes which were determined by Fourier analysis of line shapes. It was found that microstrains annealed out prior to recrystallization but that secondary extinction began to change significantly only after the domain size had increased to about 700 Å. Thus there must be a considerable decrease in dislocation density prior to the misorientation changes which accompany secondary extinction increases in copper. It was found possible to predict the strength changes during annealing of copper from the secondary extinction changes associated with x‐ray integrated intensity; this is of considerable practical importance for thin sheets.

ISSN:0021-8979    

DOI:10.1063/1.1658066

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Transmission electron images of extrinsic‐intrinsic fault pairs in a Fe&sngbnd;Cr&sngbnd;Ni alloy are shown to be sensitive to changes in the sign of (g·b)sfor reflections producing either line or stacking‐fault contrast. This is interpreted in terms of the overlapping strain fields of the three closely spaced partial dislocations. A differential treatment of the measured widths of the intrinsic and extrinsic faults indicates that the stacking‐fault energy ratio &ggr;e/&ggr;i=1.6 in this alloy.

ISSN:0021-8979    

DOI:10.1063/1.1658067

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Extrinsic photoconductivity on plastically deformed germanium containing predominantly pure edge dislocation arrays were investigated. Conductivity and transient and steady‐state photoconductivity were measured on Hall‐type samples for current flow parallel and perpendicular to the dislocations. Dislocation photoresponse was observed to be strongly anisotropic with slow nonexponential decay requiring many minutes to achieve steady state at nitrogen temperature. The results are consistent with grain boundary‐type potential barriers forming on active slip planes as edge dislocations accept electrons. The spectral response indicates a band of dislocation acceptor states with the majority of trapped electrons located 0.4 to 0.6 eV below the conduction band.

ISSN:0021-8979    

DOI:10.1063/1.1658068

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The elastic, piezoelectric, and dielectric constants of single crystals of rubidium dihydrogen phosphate (RbDP) have been measured in the temperature range of 20°–80°C. The six elastic constants, in mks units, measured at 25°C areS11=18.3×10−12,S12=2.2×10−12,S13=−1.3×10−12,S33=22.9×10−12,S44=87.6×10−12,S66=285.8×10−12,The relative dielectric constantsK11andK33are 47 and 28, respectively. The piezoelectric constantsd14andd36, in mks units, are 3.0×10−12and 26.7×10−12, respectively. As in ADP, piezoelectric activity in theXplane is very small. Since the temperature coefficients of frequency of cuts in theZplane are in excess of −200 ppm/°C, these crystals are not useful for electromechanical application.

ISSN:0021-8979    

DOI:10.1063/1.1658069

出版商:AIP    

年代:1969

数据来源: AIP