摘要:

Thermal depolarization current (TDC) of polypyromellitimide film was measured in order to obtain knowledge of the charging and discharging mechanisms of carriers in polypyromellitimide. Two peaks are observed at 173 (&agr;) and 50 °C (&bgr;) in the dried film. The &bgr; peak attributed to dipole orientation polarization is probably associated with residual reactive groups in polypyromellitimide. The &agr; peak shows nonlinear dependence on polarization electric fieldEp. The sign of the current changes with small collecting electric fieldEcwhich is applied during the TDC measurement. The &agr; peak depends on electrode materials. The &agr; peak is considered to be attributed to space‐charge polarization due to trapping of electrons injected from the cathode in the vicinity of the polymer film surface. The nonlinearEpdependence of the &agr; peak can be described by a two‐site hopping model.

ISSN:0021-8979    

DOI:10.1063/1.324657

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The effect of uniaxial stress up to 400 MPa (4 kbar) on a number of mechanical and dielectric properties of Ba0.92Ca0.08TiO3ceramic has been studied. The various results have been interpreted in terms of domain reorientation processes (90° switching) which occur in response to the applied stress. The measurements made include the following: (1) logitudinal sound velocity normal to the stress direction at 23 °C, (2) mechanical strain parallel and normal to the stress direction at 23 °C, (3) dielectric constant &egr;3parallel to the stress direction at 23 °C, (4) &egr;3as a function of temperature in the range 23–160 °C at various stress levels, and (5) electrical hysteresis loops at 23 °C with poling field parallel to the stress direction. The samples used in experiments (1) – (4) were unpoled. Experiments (1), (2), (3), and (5) indicate anomalous behavior in the 0–200‐MPa range which can be explained qualitatively in terms of domain reorientation effects, and this interpretation has been confirmed by annealing experiments which rerandomize the domains. Experiment (4) shows that the Curie temperatureTcincreases with increasing stress. This is to be contrasted to the decrease ofTcas a function of hydrostatic pressure and can again be explained as due to domain reorientation effects. For experiments (1) – (3), a quantitative calculation has been made of the magnitude of the anomalies to be expected for complete reorientation by utilizing a modified Voigt averaging scheme, and the results are in good agreement with the measured values.

ISSN:0021-8979    

DOI:10.1063/1.324658

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The numerical solution of the Clausius‐Mossotti problem for the permittivity of a suspension of perfectly conducting spheres in a cubic array is presented for sc, fcc, and bcc lattices. The results apply to electrical permittivity, magnetic permeability, electrical and thermal conductivity, and particle diffusivity. The calculations are compared with the Clausius‐Mossotti relation. Rayleigh’s equation is corrected and compared with the numerical results. A simple interpolation formula for the permittivity of a medium of perfectly conducting spheres in a simple cubic lattice is found to give an excellent approximation at all volume ratios.

ISSN:0021-8979    

DOI:10.1063/1.324659

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Laser‐induced changes in the extraordinary index of refraction (optical damage) in ferroelectrics are caused by macroscopic charge separation produced during laser illumination. If the sample is heated in the vicinity of the laser beam, pyroelectric fields are produced in ferroelectrics which can also produce macroscopic charge separation. We report the observation of the continuous transition in LiNbO3between macroscopic charge separation associated with optical damage and pyroelectricity. Macroscopic charge separation due to pyroelectricity represents a second source of optical damage in ferroelectrics which can occur whenever the temperature of the sample is raised significantly (32 °C for LiNbO3).

ISSN:0021-8979    

DOI:10.1063/1.324660

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Equations are derived for the transmittance and reflectance of a coated substrate of finite thickness. These equations are valid for thick substrates and thin films whose surfaces are specularly reflecting. It is found that the results are in good agreement with spectrophotometer readings of corresponding laboratory samples. Based upon the present results, a simple technique for calculating the refractive index of thin films from photometer readings is given.

ISSN:0021-8979    

DOI:10.1063/1.324661

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In GaAs1−xPx : N, the composition parameterxstrongly affects both the spectral position of the photoluminescence and its absolute intensity. There has previously been some controversy in the literature regarding the identification of the observed emission. The present work describes the changes in wavelength, intensity, and relative strength of spectral features at 77 and 296 K as a function of alloy composition in the range 0.6<x<1. The edge emission at 77 K can be identified in terms of contributions from isolated nitrogen atoms and from pairs of nitrogen atoms, together with optical‐phonon replicas of the exciton transitions.

ISSN:0021-8979    

DOI:10.1063/1.324662

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new and general method has been developed by which the optical activity of crystals can be measured along different directions from the optic axes. The principle of the method is to measure accurately the intensity of emergent light from parallel and crossed polarizers between which the specimen is properly oriented. The experimental apparatus is relatively simple and needs no elaborate machinery. By this method, gyration and birefringence can be obtained simultaneously as a function of wavelength. As a test of the applicability of the method, a component of the gyration tensorg11and birefringencene−n0of quartz have been observed as a function of wavelength, e.g.,g11=5.69×10−5, andne−n0=9.15×10−3at a wavelength of 550 nm. This method was also applied to the study of the optical activity of KH2PO4. It was found that the nonenantiomorphousD2dphase (paraelectric) of KH2PO4is optically active,g11=2.28×10−4at a wavelength of 506 nm.

ISSN:0021-8979    

DOI:10.1063/1.324663

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The mirror‐substrate method was used for measuring the penetration depth of 0.5–3‐keV electrons in solid hydrogen and deuterium. The penetration depth was found to be 0.53×1018E1.72molecules/cm2with the energy given in keV. There was satisfactory agreement with other data. The measurements also showed that the escape depth for true secondary electrons from solid deuterium is less than 50 A˚, which agrees well with the small values for the secondary‐electron‐emission coefficient found for solid deuterium. Results were furthermore obtained for the electron‐reflection coefficient for the gold substrate, i.e., the number of electrons that are reflected with high energies. The electron‐reflection coefficient agrees well with other results, both with respect to magnitude and energy dependence.

ISSN:0021-8979    

DOI:10.1063/1.324609

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Dislocation‐free InP and GaAs crystals have been grown by liquid encapsulation by means of an ’’impurity doping’’ procedure. It was found that grown‐in dislocations were diminished when the crystals were pulled from melts to which certain kinds of impurities were added. The impurity effect on grown‐in dislocation density was examined for Zn, S, and Te in InP, and Zn, S, Te, Al, and N in GaAs. It was found that these impurities were effective for reducing the grown‐in dislocation density, except for Zn in GaAs. The effectiveness of impurities for reducing the dislocation density of the crystals was ascribed to the strength of the bonds formed between the substitutional impurity atoms and host crystal atoms surrounding the impurity atoms. The anomaly of Zn in GaAs was presumed to originate from the interstitial Zn.

ISSN:0021-8979    

DOI:10.1063/1.324610

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The process of making amorphous ribbon by impinging a liquid jet on a substrate to form a steady‐state puddle from which the ribbon is drawn out by the moving substrate is examined. It is shown that lateral variations in the thickness of the ribbon across its width at any particular ribbon section are directly related to the puddle shape at an instant of time. Longitudinal dimensional variations in the thickness or width of the ribbon along its length indicate an unstable puddle whose shape varied with time. These longitudinal dimensional variations can be minimized by using nozzle geometries, jet velocities, and puddle sizes that induce uniformity and steadiness in the fluid flow. Various means to achieve such uniformity are suggested.

ISSN:0021-8979    

DOI:10.1063/1.324611

出版商:AIP    

年代:1978

数据来源: AIP