摘要:

The spatial intensity distribution of 8.9‐GHz longitudinal ultrasonic pulses propagating along the trigonal axis of LiNbO3has been measured between 80° and 475°K by means of Brillouin scattering. The absolute attenuation coefficient &Ggr; varied from 8±1 dB/cm at 80°K to 31±2 dB/cm at 475°K. Above 150°K, the attenuation could be fitted by &Ggr;=0.53T0.66dB/cm. Examples are given of other applications of the scattering technique.

ISSN:0021-8979    

DOI:10.1063/1.1657994

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The electromechanical coupling constantsk31andk15of single‐crystal, photoconductive CdS were obtained, respectively, by resonance‐antiresonance and shear wave velocity measurements. The correlation between the magnitude of these measured electromechanical coupling constants and the presence of thermal equilibrium resistivity inhomogeneities observed with the electron mirror microscope is described.

ISSN:0021-8979    

DOI:10.1063/1.1657995

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The source image distortion (SID) technique has been used to measure the stresses produced by electron beam melting of small regions of single‐crystal silicon wafers. Stress values thus calculated (∼108Nm−2) agree with other worker's results for stress levels close to the fracture point for single‐crystal silicon. For wafers which had fractured, no source image distortion was visible indicating the absence of stress in those wafers.

ISSN:0021-8979    

DOI:10.1063/1.1657996

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A method of growing large high‐purity Gd single crystals has been developed utilizing a distillation chamber completely sealed by molten Gd. Resistance ratios [&rgr;(294 K)/&rgr;(4.2 K)] up to ∼160 have been attained from a starting point of ∼30 in a single distillation run with the resultant crystal grains approaching a cubic centimeter in volume.

ISSN:0021-8979    

DOI:10.1063/1.1657997

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Decrease of stress level at a given strain with increase of strain rate is discussed in terms of three theories: the Johnston‐Gilman theory of yield and flow, diffusional aging mechanisms, and stress induced structural instability. None of these theories explain inverse rate effects. However, a modified concept of stress‐induced structural instability in conjunction with the Johnston‐Gilman theory provides a physical mechanism whereby a material is expected to display ordinary rate effects at high or low strain rates, but may exhibit inverse effects over some intermediate range of strain rates, depending upon the degree of structural instability.

ISSN:0021-8979    

DOI:10.1063/1.1657998

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Thin polycrystalline films made from a base composition of Pb0.92Bi0.07La0.01(Fe0.405Nb0.325Zr0.27) O3exhibited a spontaneous polarization of 10 to 20 &mgr;C per square centimeter, hysteresis‐loop squareness ≥0.75, coercivity≤15 kV/cm, Curie temperature≃150°C, resistivity≃1011&OHgr;·cm, and initial dielectric constant of about 1000. In a pulsed‐life test, one such film was repetitively switched in 300 nsec by 20‐V applied pulses for more than 2×1011polarization reversals before the test was terminated for convenience.

ISSN:0021-8979    

DOI:10.1063/1.1657999

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The self‐diffusion isotope effect has been measured by serial sectioning in the &agr;, &ggr;, and &dgr; phases of iron. Values for the isotope effect assuming a single vacancy exchange are 0.71±0.06 at 1452°C (bcc); 0.79±0.05 at 1338°C (fcc); 0.69±0.14 at 869°C (bcc). Thus, in each case the isotope effect equals the correlation factor within experimental error. Measurements at 720° and 770°C appear to be influenced by diffusion along grain boundaries producing a marked reduction in the apparent isotope effect.

ISSN:0021-8979    

DOI:10.1063/1.1658000

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Arsenic radiotracer diffusions have been performed both in intrinsic and in homogeneously doped extrinsic silicon single crystals. Under intrinsic conditions, the tracer diffusion coefficient may be represented by the expressionDi=60 exp (−4.20 eV/kT) cm2/sec. Measured in extrinsic silicon, in the absence of a concentration gradient, the tracer diffusion coefficient conforms with the relationshipD=Di(n/ni), in which (n/ni) in the ratio of the free electron concentration in the extrinsic sample to that of intrinsic silicon at the diffusion temperature.

ISSN:0021-8979    

DOI:10.1063/1.1658001

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The tracer diffusion of64Cu in lithium has been measured. The results are expressed byDCu&sngbnd;Li=(0.47±0.11) exp[(−9.22±0.22)/RT] (cm2/sec).Copper diffuses faster than any other hitherto investigated impurity in lithium; close below the melting pointDis about 2×10−6cm2/sec. From the magnitude of the diffusivity, from the systematics among the noble metals, and from parallels with diffusion results in certain polyvalent matrices, it is inferred that Cu, Au, and Ag impurities in Li diffuse as interstitials.

ISSN:0021-8979    

DOI:10.1063/1.1658002

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Positive corona streamers are observed photographically and by a photomultiplier in a 3.17 cm point‐to‐plane gap which has a third electrode (a metal ring or disk with a center hole) placed 1.50 cm from the point between the point and plane. The experiments are conducted in room air at room temperature and pressure. Streamers are triggered by voltage pulses superimposed on the direct voltages (sufficiently large that visible steady corona occurs at the 40 &mgr; radius point tip but too small to permit breakdown between any of the electrodes) applied to the gap. For the voltages considered, the experiments support the conclusions and model of Dawson and Winn as opposed to the model of Wright and the evidence of Nasser in that the streamers easily pass through the ring, showing that the streamers do not drastically distort the potential distribution in the gap as they propagate. However, the experiments also show that the value of the electric field far from the point (between the disk and plane) significantly affects the distance a streamer propagates, an effect ignored by Dawson and Winn, and that for a field value of 4.6 kV/cm between the disk and plane, many of the triggered streamers propagate completely across the gap.

ISSN:0021-8979    

DOI:10.1063/1.1658003

出版商:AIP    

年代:1969

数据来源: AIP