摘要:

The applicability of the Lifshitz‐Slyozov model for predicting phosphorus precipitation rates in the phosphorus‐SiGe system is investigated. Model parameters are determined from short‐term anneals of less than 2000 h for SiGe alloys varying in silicon content from 67 to 81 at.% and prepared by zone leveling or hot pressing. Using these parameters in the model, resistivity changes are predicted for phosphorus‐doped SiGe thermoelectric elements which had been life tested from 4000 to 40 000 h. It is concluded that the Lifshitz‐Slyozov model is applicable to the phosphorus‐SiGe system. The results of this study can be used to calculate long‐term degradation of thermoelectric performance in SiGe alloys due to phosphorus precipitation.

ISSN:0021-8979    

DOI:10.1063/1.1663600

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The effects of neodymium‐dopant additions on the behavior of dislocations in calcium fluoride were studied. Velocity measurements were carried out on edge and screw dislocations as a function of stress, temperature, and dopant content. It was observed that screw dislocations can be the more mobile type in CaF2, depending on the stress and concentration of aliovalent impurities present. The mobility of screw dislocations relative to edges was reduced significantly by 70 ppm Nd3+. An apparent transition in the drag mechanism from extrinsic to intrinsic was observed for edge dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1663601

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The microscopic relaxation parameters, activation energy and lifetime, are measured for the single‐and double‐dipolar systems KCl : Eu++and KCl : Eu++, Yb++using both ac bridge and ionic thermocurrent (ITC) techniques. The two methods are compared and contrasted. A theory is developed to calculate dielectric constant and loss tangent for the single and double systems from the measured ITC, and comparisons are made with bridge measurements. The theory of peak cleaning, used in the ITC technique, is also presented.

ISSN:0021-8979    

DOI:10.1063/1.1663602

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Copper and gold evaporated films of thicknesses between 500 and 2500 Å have been bombarded at liquid‐nitrogen temperature with 4–10‐keV He ion beams. The electrical resistivities of these films increase with dose without saturation, and the values of these changes in the thinner films approach tens of &mgr;&OHgr; cm at a dose of 1017ions/cm2. About 80% of the resistivity changes induced in copper and about 60% of the resistivity changes induced in gold are recovered after annealing to 453 K. The remarkable peaks of the thermal recoveries are mainly observed in stage II. The nature of the evaporated metal films closely relates to the large resistivity changes, which are also affected by bombarding with low‐energy ions.

ISSN:0021-8979    

DOI:10.1063/1.1663603

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The attenuation of longitudinal ultrasonic waves originating from their interaction with phonon gas and from other thermoelastic causes has been evaluated in CsCl, CsBr, and CsI at 300°K by using second‐order elastic moduli and third‐order elastic moduli, in the ⟨100⟩ and ⟨110⟩ directions, and shear waves polarized along the ⟨100⟩ and ⟨11¯0⟩ directions. The phonon viscosity and dislocation drag along the ⟨100⟩ and ⟨110⟩ directions are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1663604

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Bias (dc electric field) dependence of the dielectric constant of ferroelectric ceramics of the Pb(Zr,Ti)O3type has been investigated. Measurements were carried out at various temperatures in the ferroelectric phase and at several frequencies between 1 kHz and 1 MHz. The bias characteristics of the dielectric constant show a temperature‐dependent asymmetry in the electric field direction. A model in which the coercive fields of the 180° and 90° domains are distributed around some average value is considered. The total dielectric constant of the material is calculated by considering the contributions of each type of domain, taking into account the difference between the differential and incremental dielectric constants. This model explains the dependence of dielectric constant on electric field. A comparison of the calculated and experimental results is presented.

ISSN:0021-8979    

DOI:10.1063/1.1663605

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The generation of dislocation loops around spherical second‐phase particles by various models is examined. A theoretical lower limit to the critical misfit is obtained and it is found to agree with the experimentally observed values.

ISSN:0021-8979    

DOI:10.1063/1.1663606

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Ultrasonic velocity and attenuation measurements have been made by traveling‐wave methods on several refractory metals and their alloys. Broad‐band pulses centered around 120 kHz were used for extensional waves (and some torsional waves) in wire specimens. Elastic moduli calculated from the velocities decrease with increasing temperature; the slope increases in magnitude at about half the absolute melting point. At the same point, the attenuation begins to increase rapidly and peaks 300–600°C above the breakpoint. These effects are ascribed to absorption in grain boundaries. The transit time versus temperature in rhenium wire has been calibrated for the use of rhenium as an ultrasonic thermometer sensor. Ultrasonic thermometry above 2000°C is an application of the present measurements.

ISSN:0021-8979    

DOI:10.1063/1.1663607

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A phenomenological model of contact activation is presented based on diffusion of trace gaseous pollutants. The chemistry of these gases when adsorbed on the contact surface is discussed. Contact operating rates, gaseous pollutant concentrations, and contact surface roughness are considered. Experiments are performed and discussed which involve the decomposition of inorganic halogenated compounds and hydrocarbon compounds, the chemical effects of these compounds when on palladium contacts with protection circuits, and the rate of operation of contacts. Experimentally, an attempt is made to simulate conditions as they are found in the field whenever possible. The results of these experiments show that both classes of compounds can activate and thereby cause contact erosion when they are present at the ppm level. It is further shown that a 1‐Hz versus 10‐Hz relay operating rate can increase average arc time by typically a factor of 10 when 1 ppm of selected gaseous impurities are present in the atmosphere around the contact. These results fit the model as presented, agree with data collected from the field, and are capable of explaining erosion rate differences between the field and various life tests.

ISSN:0021-8979    

DOI:10.1063/1.1663608

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The thermal conductivity of a semimetal Mg2Pb single crystal has been measured from 2 to 200 K. At low temperatures thermal conduction is by phonons limited by phonon scattering from the heavy hole Fermi surface. At higher temperatures the thermal conductivity contains both electronic and phonon contributions. A comparison of the thermal conductivity of Mg2Pb with the thermal conductivities of the related semiconductors, Mg2Si, Mg2Ge, and Mg2Sn, indicates that there is a significant bipolar contribution to the electronic thermal conductivity.

ISSN:0021-8979    

DOI:10.1063/1.1663609

出版商:AIP    

年代:1974

数据来源: AIP