摘要:

The dynamic elevated temperature elastic properties of single‐crystal and polycrystalline aluminum have been studied by employing a laser pulse technique to produce propagating stress pulses in slender rods. The behavior at temperatures between 25 and 500°C of monocrystals and slender polycrystalline specimens having a cold work texture is described. Experimental results are presented for the polycrystals as a function of thermomechanical history and compared to the results for single crystals of known orientation. The results are evaluated in terms of dislocation dynamics and anisotropy of the lattice in single crystals and polycrystals. Results show that the longitudinal wave velocity increases with the annealing of dislocations and then decreases with the disappearance of texture in polycrystals.

ISSN:0021-8979    

DOI:10.1063/1.1662131

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have investigated the voltage tuning ofb‐axis CdS phonon masers. Voltage modulation is found to be a fairly complex phenomenon involving amplitude as well as frequency modulation of the phonon maser output. Near threshold, the frequency modulation is typically of the order of 10 kHz/V. The response is flat up to frequencies of the order of the reciprocal of the acoustic transit time. At the higher driving voltages, the tuning is reduced. The device appears promising as a FM communications transmitter.

ISSN:0021-8979    

DOI:10.1063/1.1662132

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple theory of the coupled semiconductor‐piezoelectric convolver is given and compared to a full theory by Otto. The approximations used are valid over the interesting experimental range. For YZ&sngbnd;LiNbO3and silicon, the range of validity of our theory corresponds to &sgr; > 0.5 mho/m andf< 500 MHz.

ISSN:0021-8979    

DOI:10.1063/1.1662133

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have theoretically studied the propagation of guided waves in anisotropic media, and have obtained approximate results for two particular planes. The two waves that can propagate have a structure very close to classical waves, and the difference in wavelength for every mode is given.

ISSN:0021-8979    

DOI:10.1063/1.1662134

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have given formulas for the determination of the rotation and the ellipticity of a wave that has propagated through a quartz sample in a waveguide. Taking into account the multiple reflections, calculations made with the help of a computer were compared with the experimental results. Dielectric constants of quartz are found to be 4.63 parallel and 4.51 perpendicular. Both results are believed to be correct to ± 0.7%.

ISSN:0021-8979    

DOI:10.1063/1.1662135

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The range of the intrinsic nonstoichiometry in lead zirconate‐titanate at 1100 °C has been established independently by two gravimetric techniques. A modified Knudsen effusion experiment allowed for an extended interpretation of the vapor pressure data. A single experiment was used to determine the width of anyPb1−x□x (TiyZr1−y)O3−x&phgr;xsingle‐phase region, the equilibrium PbO vapor pressure, activity data as a function of both temperature and composition, and the exact location of the stoichiometric composition within the single‐phase region. The ``vapor phase equilibration'' (VPE) method was used as a supplemental measurement of the width of most PZT single‐phase regions. Results obtained by the two methods for the extent of nonstoichiometry were in close agreement (xmax= 0.10 aty= 1.0;xmin= 0.016 aty= 0.40;T= 1100°C). The Knudsen effusion experiment established that for all the compositions studied, the stoichiometric composition, Pb(TiyZr1−y)O3, was coincident with the (liquid + PZT) phase boundary.

ISSN:0021-8979    

DOI:10.1063/1.1662136

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We report a study of the morphology and kinetics of crystallization of films ofa‐Se vapor deposited on mica substrates. Morphological examination was facilitated by the complete dissolution of the amorphous component of the films by CS2, while the crystalline component was left essentially intact. Crystallization begins (in the temperature range 30–100°C) with the formation and radial growth of crystalline aggregates, with a cylindrite (two‐dimensional analog of spherulite) morphology, at the mica‐film interface. Filamentary crystals stem from the less regular regions of these cylindrites and grow upwards through the film. Upon reaching the vicinity of the free surface, some of the filamentary tips develop into cylindrites which grow in and parallel with the free‐surface plane. The interface cylindrites were about 500 Å thick and their presence apparently is responsible for the phenomenon of ``visual'' darkening often seen ina‐Se films. They are composed of small crystal domains each oriented so that the Se chain axes are parallel with the interface and perpendicular to the disk radius. In the regular morphology, favored by higher‐temperature crystallization, the domains are stacked into lamellae which extend radially from the inner regions to the outer edge of the cylindrites. These lamellae are interconnected by less regularly oriented domains and are much thicker and less regular in cross section than the crystals formed by linear polymers. The radial growth rates of the regular interface cylindrites in films of the highest purity were constant in time and quite reproducible at a given temperature. They are among the highest rates reported fora‐Se and about two orders of magnitude higher than the corresponding rates for free‐surface cylindrites. Their temperature dependence is described byu= 6 × 1015exp[(− 32.7 kcal/mole)/RT] cm/sec.

ISSN:0021-8979    

DOI:10.1063/1.1662137

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The driving forces for shape changes and diffusion in nonhydrostatically stressed solids have been distinguished. The driving forces for shape changes are related to differences in the chemical potentials of the components of the solid that are defined at the surfaces, e.g., by their vapor pressures, whereas the driving forces for volume diffusion are gradients in the chemical potentials of the components within the solid. For homogeneously but nonhydrostatically stressed solids that are uniform in state throughout, the former potentials are multivalued and directly measurable (e.g., vapor‐pressure measurements), whereas the latter potentials are unique functions of the state of the solid. In general, no meaningful connection exists between the two sets of potentials. However, for situations in which, for example, the shape of a solid is changing by volume diffusion, the variations in the two sets of potentials become continuously connected.

ISSN:0021-8979    

DOI:10.1063/1.1662138

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The Hall coefficientRof single crystals of vanadium carbide (VCx) with carbon‐to‐metal ratios (x) ranging from 0.83 to 0.88 were measured between 4.2 and 300 K. The behavior ofRversusTis found to depend critically onx, as well as the type of ordered structure (V8C7or V6C5) present. The data are interpreted in terms of a two‐band model which allows for the effects of anisotropic scattering. It is proposed that a minimum inR (x)atx= 0.875 (V8C7) results from an increase in relaxation time, rather than a change in band structure for the ordered compound. The two‐band analysis is consistent with the specific heat data of Lowndes, Finegold, and Lye which show a maximum in the density near the ordered compound V6C5.

ISSN:0021-8979    

DOI:10.1063/1.1662139

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The annealing kinetics of sputtered Au&sngbnd;W and Au&sngbnd;Mo films have been investigated as a function of temperature up to 500°C. The electrical resistivity of the gold layer after deposition was measured to be 1.25 times the bulk resistivity. The excess resistivity was attributed to structural defects such as vacancies, interstitials, twins, dislocations, and impurities which were quenched in during deposition. Particle size changes in Au&sngbnd;W and Au&sngbnd;Mo occur in two stages, with an activation energy for gold of 0.4 eV below 200°C and 0.7 eV above 200°C. The activation energy for the refractory layer particle growth was 1.8 eV up to 500°C. The kinetics of dislocation (Nd) annealing at 500°C was determined to follow an equation of the formQ(Nd)= −A(Nd)m, withm= 3. Annealing the films up to 500°C resulted in a decrease of internal stress in gold from 2.5 × 109dyn/cm2. The observed results are discussed in terms of microstructural changes and the dependence of internal stress on film thickness.

ISSN:0021-8979    

DOI:10.1063/1.1662140

出版商:AIP    

年代:1973

数据来源: AIP