摘要:

The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has recently been reported in hexagonal crystals by Bleustein and Gulyaev. It is shown that similar waves can exist in cubic crystals of4¯3mand 23 classes, along [110] direction on the(1¯10)plane and their equivalent orientations. Velocity equations for the piezoelectric surface wave and the elastic surface wave are derived and their characteristics discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659217

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Calculations for the phase velocity of acoustic surface waves on lithium niobate with a contiguous gold layer have been carried out for the fundamental and higher‐order modes of propagation. The anisotropy of the substrate leads to a prediction that the first higher‐order mode has a low‐frequency cutoff. In some cases the phase velocity dispersion curves for various modes have crossing points. Theoretical calculations and experimental evidence of the position of the crossing points for the first two modes and the phase velocity characteristics of the dominant mode above and below the crossing points as a function of the frequency‐film thickness product are given.

ISSN:0021-8979    

DOI:10.1063/1.1659218

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The ``propagating wave'' analysis of an ultrasonic resonator is extended to include some effects of nonparallelism, guided wave phenomena, and electrical loading. Each of these effects contributes an ``inhomogeneous'' broadening to the continuous wave frequency domain response and an ``inhomogeneous'' damping to the time domain decay. Experimental verification for ultrasound propagating in both thin and bulk solid specimens is obtained by utilizing the sampled‐continuous wave ultrasonic spectrometer. Quantitative evaluation of interference effects among harmonic and inharmonic responses is achieved using the spectrometer in the time domain mode of observation.

ISSN:0021-8979    

DOI:10.1063/1.1659219

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Microwave emission fromn‐GaAs crystals, under conditions of current instability with propagating acoustoelectric domains, was detected and analyzed for various stages of the total acoustic flux level in such domains. Frequency range covered extended from 0.2 to 4.5 GHz. Diagnostic experiments indicate that the emission is due to the electromechanical conversion of the acoustic flux as the propagating domain hits the anode. The frequency spectrum of the emission shows various peaks that can be identified as sub‐harmonics and sum frequencies. The experimental result is consistent with the theory of parametric conversions.

ISSN:0021-8979    

DOI:10.1063/1.1659220

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Acoustical waves have been observed in CO2, at initial pressures between 2 and 25 Torr, caused by sudden heating from incident CO2laser pulses. The effect was observed by monitoring the temperature increase of the window of the absorption cell due to the incident sound wave. Results indicate that the influence of a high‐power laser beam upon the penetrated atmosphere—and the feedback of the disturbed atmosphere on the propagation of the laser beam—may be conveniently studied under simulated laboratory conditions.

ISSN:0021-8979    

DOI:10.1063/1.1659221

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Effects of particle size and particle shape have been studied in the infrared absorption spectra of BaTiO3and SrTiO3powders to determine whether previously developed methods to treat such effects are applicable to crystals having high dielectric constant and ``soft'' lattice modes. The spectrum of both materials exhibits three absorption bands (BaTiO3: 545, 400, and 180 cm−1; SrTiO3: 605, 400, and 175 cm−1) that are considerably removed from the TO‐mode frequencies computed from bulk single‐crystal reflection data (BaTiO3: 510, 183, and 33.8 cm−1; SrTiO3: 546, 178, and 87.5 cm−1). These frequencies were successfully correlated with the bulk‐crystal frequencies by use of classical electromagnetic scattering theory and an extension of Fro¨hlich's method. The low‐frequency ``soft'' modes of both crystals were found to have an unusually large dependence on particle shape with the consequence that the powders absorb radiation at the corresponding LO‐mode frequency.

ISSN:0021-8979    

DOI:10.1063/1.1659222

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

All of the elastic stiffness constants exceptc13have been found to decrease almost linearly with temperature between −120° and 120°C. The constantc13reaches the maximum in the vicinity of 0°C, above which it also decreases with temperature. On the other hand, the effective elastic constant (c11–c12)/2, which corresponds to the exceptionally slow shear wave propagating along [110], increases with temperature. The shear wave propagating in the (001) plane making angle of 35.9° with theXaxis has zero temperature coefficient of velocity. Acoustic absorptions for several sound modes vary within 1 dB/cm for both the longitudinal wave (measured at 36 MHz) and shear wave (48 MHz) in the measured temperature range. Both real and imaginary parts of the dielectric constants increase monotonically with temperature, while the piezoelectric constantd14decreases in the temperature range between −150° and 180°C.

ISSN:0021-8979    

DOI:10.1063/1.1659223

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A new technique for improving the accuracy of the angular orientation of nonsymmetry plane dHvA data on cubic systems by an order of magnitude (from 2.0° to 0.2°) has been developed. The extension of this technique to orienting dHvA data in noncubic crystallographic systems, or to orienting data for other types of experiments, viz. neutron scattering, should be straightforward.

ISSN:0021-8979    

DOI:10.1063/1.1659224

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The use of LiNbO3crystals in nonlinear optical experiments has been limited by the lack of long, high‐quality crystals. We have shown that crystals grown from a congruent composition melt are significantly less susceptible to birefringence variations which in the past have limited the useful phase‐matchable lengths of LiNbO3crystals. Both a birefringence test which directly measures the spatial birefringence of the crystal and a second harmonic generation test were used to evaluate crystals grown from melts of various compositions. Crystals with less than 10−5variation in birefringence over a length of 4 cm have been obtained repeatably when grown from congruent melts.

ISSN:0021-8979    

DOI:10.1063/1.1659225

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Results obtained by neutron diffraction indicate that the magnetic moment of the ferromagnetic sublattice in the Laves phase structures, C15 (ErCo2, ErAl2) and C14 (ErCoAl), varies with composition while the ordering temperatures stay approximately constant. Low values of the aligned moment, however, are accompanied by high values of the disorder scattering at low temperatures. Co carries no moment from 30 mole % ErAl2on. Results are discussed in terms of tendencies toward antiferromagnetism at certain values for the valence electron concentration.

ISSN:0021-8979    

DOI:10.1063/1.1659226

出版商:AIP    

年代:1970

数据来源: AIP