摘要:

Strain centers with attendant prismatic dislocation loops have been studied in copper crystals of low dislocation density by use of Borrmann x‐ray topograph and etch‐pit techniques. Direct comparison of these defects with the two techniques showed an exact correlation. While the nature of the centers of the strain could not be certainly determined, there was evidence that the loops were of the interstitial type.

ISSN:0021-8979    

DOI:10.1063/1.1657830

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A model is given for diffraction by an fcc lattice which contains a randomly arranged mixture of intrinsic and extrinsic stacking faults. The expression for the distribution of intensity in reciprocal space contains, as special cases, the equations derived for intrinsic and extrinsic faulting by Paterson and by Johnson, respectively. The result and its derivation clarify a controversy which arises from Sabine's model for faulting by condensation of interstitials; some comments on this problem are given in an appendix.

ISSN:0021-8979    

DOI:10.1063/1.1657831

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The room‐temperature spontaneous polarizations in LiNbO3, LiTaO3, Ba2NaNb5O15, Sr0.5Ba0.5Nb2O6, Ba1.1Sr0.9NaNb5O15, and Sr2KNb5O15have been measured directly by a pulsed field method using an aqueous solution of LiCl as the electrode material. The experimental results are:P8(LiNbO3) = 0.71±0.02 C/m2,P8(LiTaO3) = 0.50±0.01 C/m2,P8(Ba2NaNb5O15) = 0.40±0.01 C/m2,P8(Ba1.1Sr0.9NaNb5O15) = 0.36±0.01 C/m2,P8(Sr2KNb5O15) = 0.25±0.01 C/m2, andP8(Sr0.5Ba0.5Nb2O6) = 0.25±0.01 C/m2. Experimental techniques are presented, and the advantages of the pulsed‐field method over hysteresis‐loop methods are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1657832

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The variation of the piezoelectric constantd11of quartz has been measured from 22°C to near the transition temperature 573.3°C (highest recorded measurement, 565°C). The quartz was mounted on a metal anvil and its piezoelectric response was excited by dropping a steel ball onto the center of the quartz disk. At room temperature, a value ofd11was found to be −2.16×10−12C/N with a standard deviation of 0.11×10−12. From 20°–200°C, the magnitude ofd11decreases linearly at −4.5% per hundred degrees, in close agreement with the behavior observed by Langevin. Above 200°C, the value decreases sharply, following a smooth curve and reaching zero in the near vicinity of 573.3°C.

ISSN:0021-8979    

DOI:10.1063/1.1657833

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The scattering amplitude for x‐ray diffraction by a vibrating crystal is obtained. The Bragg diffracted propagators for the perfect crystal are replaced by new propagators in which the Fourier transform of the polarizability of the crystal,v(H), is multiplied by the Bessel function of zero order,J0(H·Aq), of the product of the vibrational amplitudeAqand a reciprocal lattice vectorH, in a similar fashion to the correction by the Debye‐Waller factor in the thermal problem. The scattering amplitude contains both dynamical and kinematical contribution. The case of ideal thickness vibration is studied in detail in the Laue geometry. The real part of the perturbed scattering amplitude is proportional tov(H) sin (H·Aq). This theory elucidates the transition from dynamical to kinematical scattering, that is, a decrease in extinction, as a function of the vibration amplitude.

ISSN:0021-8979    

DOI:10.1063/1.1657834

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A model descriptive of the growth of precipitates which nucleate at grain boundaries and grow pre ferentially along them (grain‐boundary allotriomorphs) is studied. The sequential processes during growth are presumed to be volume diffusion of solute to the grain boundary, transport along the grain boundary to the precipitate, and interfacial diffusion and deposition over the surface of the growing allotriomorph. An analysis of this mode of growth is applied to the results of recent observations of the lengthening and the thickening rates of &thgr;‐allotriomorphs in an Al‐4% Cu alloy. On the basis of these measurements the diffusivity within the grain boundaryDbis found to be 0.1 exp (−18480/RT) cm2sec−1, while the diffusivity within the allotriomorph‐matrix interface,D8, isD8=1.8 exp (−22020/RT) cm2sec−1when the mole fraction of solute in this interface is taken to be the average of that in &thgr; and in &agr; at the boundary, orD8=0.06 exp (−12740/RT) cm2sec−1when this surface concentration is assumed to be simply that in &agr; at the boundary. The latter value ofD8is in good agreement with that obtained in a previous analysis where the same value was used for the interface concentration.

ISSN:0021-8979    

DOI:10.1063/1.1657835

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The lateral diffusion of Ag along a thin evaporated Te film has been studied by optical and electron microscopy. Diffusion occurred only when the Ag was at least 1.0 times the Te thickness, corresponding to the presence of sufficient Ag to form Ag2Te in the diffusion zone. Electron microscopy of the diffusion zone showed considerable grain‐boundary diffusion and this was in agreement with the observation that the growth rate had a maximum at a Te film thickness of about 80 Å when the Te structure had an optimum number of grain‐boundary paths. The activation energy for the diffusion process was found to be 10.0 kcal/mole.

ISSN:0021-8979    

DOI:10.1063/1.1657836

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The test section of an electric‐arc shock tube was used to explore the dependence of microwave breakdown behavior on elevated gas temperature. Special diagnostic techniques included microwave interferometry and a flat‐plate ion density probe. Results for air, nitrogen, and argon are in agreement with the proposed theory, and the importance of the nitrogen molecule in explaining the air data is established in the context of the theoretical model.

ISSN:0021-8979    

DOI:10.1063/1.1657837

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An analysis is presented which shows that photon‐bunching effects in a spatially coherent noise field can be enhanced by the superposition of a monochromatic coherent ``signal'' and/or by shaping the spectrum of the incident noise. For a Lorentz spectral shape, the addition of ``signal'' to noise is shown to increase bunching effects by a factor no greater than 4. By changing the noise spectrum from a Lorentz to a rectangular shape, bunching effects are shown to increase by a factor of 2 despite the fact that total incident noise power decreases. In all cases, the ratio of bunching noise to shot noise is proportional to the average number of detected noise photons per cycle of noise bandwidth. For the specific problem analyzed, the maximum value of the ratio of bunching noise to shot noise is determined. In the absence of ``signal,'' the results are found to agree with the exact distribution of Be`dard.

ISSN:0021-8979    

DOI:10.1063/1.1657838

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A modification of the Kelvin contact potential difference technique has been used to measure the temperature coefficient of the work function of three tungsten surfaces over the temperature range from 77°–1300°K. Two of the surfaces were polished and etched single‐crystal planes having the (110) and (100) orientations, the third was a sample of polycrystalline foil. The results obtained werefoil(11±1)×10−5 eV/∘K(110)(6.3±0.6)×10−5 eV/∘K(100)(9.1±0.4)×10−5 eV/∘Kand these are in qualitative agreement with predictions based on the temperature dependence of the electron smoothing component of the surface double layer.

ISSN:0021-8979    

DOI:10.1063/1.1657839

出版商:AIP    

年代:1969

数据来源: AIP