摘要:

An examination was carried out on the physical basis for the so‐called ’’extremum condition’’ which determines the dimension of transformed phases during the steady‐state cellular phase‐separation reaction. The concept of the ’’balance of forces’’ which employs the balancing of various forces at the moving phase‐separation boundary as the condition for the steady‐state cellular phase‐separation reaction is proposed. The magnitude and the direction of these forces are given by the partial derivatives of the total free‐energy reduction due to the phase change at an undercooled condition in terms of the relevant reaction parameters such as the size of the microstructure and the reaction velocity. A simple model of lamellar formation by the eutectic or eutectoid reaction is used to demonstrate the meaning of the extremum condition and also to show the usefulness of the balance‐of‐forces concept.

ISSN:0021-8979    

DOI:10.1063/1.326712

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

By rapid pulse heating of NiTi‐based shape‐memory wires, both with and without an applied load, the details of the recovery process have been studied. It is shown that, contrary to existing theories, the temperature of the reverse transformation is relatively independent of applied load. A modified hypothesis for the motion is proposed, taking into account internal stresses present in polycrystalline material. Without applied load, the reverse‐phase transformation on heating is measured to occur within 3 ms, and motion under load is shown to be largely governed by the mechanical time needed to move the weight.

ISSN:0021-8979    

DOI:10.1063/1.326713

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The appearance of positive interfacial charge at the Si‐SiO2interface in metal (Al) ‐SiO2‐silicon structures illuminated by vacuum ultraviolet (≳ 9 eV) light (Al‐negative) or subjected to electron‐avalanche injection (Al‐positive) has been found to depend on water exposure of the SiO2layer. This finding raises the possibility that these effects can be explained by the diffusion of water‐related species (especially H), rather than by the diffusion of excitons, as has been previously proposed. Although we cannot unambiguously decide whether the source of the vacuum ultraviolet effect is diffusion of excitons or water‐related species, it appears more likely that the water enhances thedetectionefficiency of the diffusing species as they reach the Si‐SiO2interface.

ISSN:0021-8979    

DOI:10.1063/1.326714

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The ionic conductivity and its thermal activation energy have been measured in Na &bgr;‐alumina using a contact‐free induced‐torque method at frequencies between 1 and 20 Hz and temperatures between 295 and 415 K. The results are in good agreement with the most recent dc contact conductivity measurements.

ISSN:0021-8979    

DOI:10.1063/1.326715

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A recently derived representation of the Gibbs free energy of a defect process in terms of the thermoelastic properties of the host crystal is shown to be applicable to the calculation of the activation volume for the diffusion of impurities in solids. The experimental data for the diffusion of several metals (Ag, Au, Cu, Hg, Zn, Sn, Tl, Ni, Pd) in lead and the self‐diffusion are discussed showing a fair agreement with the theoretically determined activation volumina.

ISSN:0021-8979    

DOI:10.1063/1.326716

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Phase formation of metal‐rich Pd silicides was studied in palladium–amorphous‐silicon thin‐film interactions by means of4He+‐ion backscattering, Auger spectrometry, electron microprobe, and x‐ray diffractometry. In the initial stage of compound formation, where both unreacted Si and Pd layers ar present, the Pd2Si phase has been observed. At increasing annealing temperature in SiO2/Si(a)/Pd systems, where the metal‐film thickness was larger than that of amorphous‐Si film, phases richer and richer in metal have been detected, following exactly the phase diagram reported in literature. The Pd‐richest phase was identified as Pd4Si and is stable up to 650 °C in the presence of unreacted Pd. A crystallographic characterization of this new thin‐film end phase was performed on the basis of a triclinic unit cell.

ISSN:0021-8979    

DOI:10.1063/1.326717

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Previous results have shown, in agreement with the silicide‐growth theory of Walser and Bene´, that VSi2is the first silicide phase to nucleate and grow at single‐crystal‐Si–V interfaces. We have found that with sputtered thin‐film‐V–crystalline‐Si or amorphous‐Si diffusion couples we can reproducibly cause either VSi2or V3Si, respectively, to nucleate and grow. V3Si and VSi2are never observed together, suggesting that bistable growth can be triggered by the initial interface. The V3Si growth was found to have at1/2dependence and V was found to be the dominant diffusing species. This implies that unlike the case of VSi2, in V3Si the diffusion constant of V is much larger than Si and growth occurs at the Si‐V3Si interface. Deposition parameters and initial sample properties such as structure and impurity content which may control the nature of the reaction phase are discussed. We also find oxygen to be rejected by a growing A‐15 phase. Samples were studied by Rutherford backscattering, Seeman‐Bohlin x‐ray diffraction, and electrical‐resistivity–vs–temperature measurements.

ISSN:0021-8979    

DOI:10.1063/1.326718

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We find that two factors bear on the high‐energy pulse degradation of a varistor’s electronic characteristic. First, the electronic structure of active grain‐boundary segments depends solely on the peak temperature occurring there during a pulse, and second, this peak temperature is determined by the thermal transport properties of the microstructure. We find that the intrinsic electronic structure can be modified without changing the microstructure to greatly improve the pulse‐degradation performance of a varistor by an anneal at low temperature (600 °C) in oxygen. The influence of microstructure is embodied in the grain‐boundary temperature‐magnification factorZgbwhich is defined, measured, and studied theoretically. Theory shows that there are three regimes: (i) a long‐pulse‐width regime whereZgb=1, (ii) a short‐pulse‐width regime whereZgb∼ (pulse width)−1/2, independent of pulse energy, and (iii) a very‐short‐pulse‐width (or high‐energy‐density) regime whereZgb∼ (pulse energy)−1/2, independent of the pulse width. The theory contains one microstructural parameter. Our data encompasses the first two regimes and agrees well with theory for a value of the microstructural parameter which is in good agreemet with earlier work.

ISSN:0021-8979    

DOI:10.1063/1.326719

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Thermal conductivity measurements of 6HSiC crystals were done in the 300–500 K range by means of radiation thermometry. Bothp‐ andn‐type crystals with carrier concentrations in the 8×1015to 1020cm−3range were used. For the purest samples it was found that the thermal conductivity normal to thecaxis is proportional toT−1.49, the room‐temperature value being 3.87 W/cm deg. It was also found that the thermal conductivity parallel to thecaxis is about 30% lower than that normal to thecaxis. Electrical data in the 100–1000 K range are also presented.

ISSN:0021-8979    

DOI:10.1063/1.326720

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The Hall effect and conductivity of Ge‐dopedp‐type AlxGa1−xAs has been studied in the temperature range from 77 to 500 K. The experimental results have been analyzed to yield the acceptor and donor concentration and the Ge activation energy. The samples have been found to be heavily compensated with an average compensation ratio of about 0.4. The activation energy was found to increase strongly with Al content forx<0.6 and to decrease with Ge concentration.

ISSN:0021-8979    

DOI:10.1063/1.326721

出版商:AIP    

年代:1979

数据来源: AIP