摘要:

Simultaneous measurements of the pyroelectric (PE) coefficient &lgr; and permittivity &egr; from the PE voltage responses to step ir radiation signals in triglycine sulphate (TGS) are reported as functions of temperature in both the ferroelectric and paraelectric phases. It is shown that the observed lowering and widening of the peaks of &lgr; and &egr;, the appearance of a PE effect in the parelectric phase, and the shift of the &egr; peak to temperatures aboveTccan be explained by the existence of an internal bias fieldEb. The values ofEbcalculated to fit the experimental results vary in different TGS samples from 30 to 150 V/cm.

ISSN:0021-8979    

DOI:10.1063/1.322344

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Various phases of the titantium rich part of the Ti‐Fe binary system were obtained by thermal treatments and were identified by Mo¨ssbauer spectroscopy and x‐ray diffraction. Room‐temperature Mo¨ssbauer parameters were derived for the following phases: &agr;m, &agr;, &Vthgr;, &ohgr;, &bgr;, and TiFe. The range of concentrations for which an athermal &ohgr; phase appears upon quenching was found to be 2.7⩽CFe⩽5 wt%. The athermal &ohgr; phase disappears during aging at 285 °C for 15 h, when the alloy containsCFe⩽4.0 wt%. Martensite &agr;mwas found to form when Fe concentrations were ⩽2.7 wt.%. After quenching from the &bgr; field, the &bgr; phase retains when the Fe content of the alloy is ⩾2.7 wt.%. The &Vthgr; phase forms during aging at temperatures above 280 °C, for alloys with a Fe content ⩽2.7 wt.%. Room‐temperature Mo¨ssbauer parameters are given to enable phases to be indentified and analyzed by means of Mo¨ssbauer spectroscopy.

ISSN:0021-8979    

DOI:10.1063/1.322297

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The energy‐reflection coefficient &ggr; has been measured for keV protons impinging on Cu, Au, and Pb and helium impinging on Si, Ag, Ta, and Pb. The results are obtained by entirely independent techniques in three different laboratories. They agree within the stated accuracies of 10%. For a given projectile, &ggr; is found to depend on the target material through the Thomas‐Fermi reduced energy &egr; only. Hence, extrapolation to other target materials may easily be performed. The results are in good agreement with those obtained from recent computer simulations.

ISSN:0021-8979    

DOI:10.1063/1.322360

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The thermal diffusivity and the relative difference in molar heat capacities, (Cp−Cv)/Cv, of polycrystalline niobium have been derived from acoustic measurements in the temperature range 60–340 K. The electrical resistivity has also been measured from 8 to 340 K; 0.833 &mgr;&OHgr; cm, 18.7, and 9.25 K being the values of residual resistivity &rgr;0, resistance ratio &rgr; (300 K)/&rgr;0, and superconducting transition temperature, respectively. The thermal conductivity, Lorenz ratio, and molar heat capacity at constant volume have been calculated for the temperature range 60–340 K, using present values of thermal diffusivity, electrical resistivity, and literature values of specific heatCp. A shallow maximum in the derived thermal conductivity curve is observed around 180 K where the Lorenz ratio assumes the maximum value 3.15×10−8W &OHgr; K−2. It is suggested that the thermal conductivity maximum may originate in the phonon contribution.

ISSN:0021-8979    

DOI:10.1063/1.322341

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Because of the existence of the factors causing shock‐associated damping effect on edge dislocations, an edge dislocation in a plane shock‐stress field may slip under special circumstances in a direction without an apparent shear component of the shock‐stress wave. In this paper the mechanism and the factors involved in this unconventional behavior of edge dislocations will be evaluated.

ISSN:0021-8979    

DOI:10.1063/1.322352

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Expressions are derived for the elastic interaction energy between void‐solute shell composites. These composites consist of spherical void cores surrounded by spherically symmetric solute shells containing a uniform concentration of irradiation segregated solute. The solutes are assumed ’’misfitting’’ and as such represent sources of internal stress. The elastic interaction energy between composites arises because of the so‐called inhomogeneity interaction and has minimum values at certain composite separations and solute shell thickness. The existence of these minima obtains largely because the misfit of the composites increases as the composite separationRincreases. For a constant misfit, the interaction energy would decrease monotonically approximately asR−6. The surface stress of voids is taken to be zero in the calculations so that the only source of interaction between composites is the stress induced by solute segregation. The calculations are performed for both two‐composite andN‐composite interactions, and we show that, primarily, only nearest‐neighbor interactions are significant. The calculations are compared with experimental investigations of void ordering in an Ni ion‐irradiated Nb‐1Zr alloy containing 0.0038 atom fraction of oxygen as an impurity. Given experimentally determined void sizes and auxiliary data, the correct void lattice parameter is predicted when the solute shell thickness is ∼30% of the composite radius. In pure Nb, it is found the O, C, or N impurities are necessary for void ordering, which supports the main thesis of the present paper, viz., solutes/impurities are a primary cause of void ordering.

ISSN:0021-8979    

DOI:10.1063/1.322308

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A study has been made of the absorption bands of silicon, irradiated with high doses of fast neutrons (E≳1 MeV), by infrared spectroscopy in the region between 200 and 4000 cm−1(50–2.5 &mgr;). The relationship between several effects [band tailing (0.2–0.5. eV), divacancy‐associated band (3.45 &mgr;m), higher‐order bands (700–1400 cm−1), and single‐phonon bands (observed at 488, 410, and 332 cm−1)] and different irradiation doses up to 1019fast neutrons/cm2has been investigated. From the results of the absorption due to band tailing it can be assumed that the crystal is not amorphous. However, the observed vanishing of the higher‐order bands at the highest doses indicates an important change in the damaged lattice. The annealing behavior up to 600 °C, at the measuring temperatures of 78 and 300 °K, showed a slower annealing out of the single‐phonon bands for the high dose. From the stressing experiments, performed for single‐phonon bands, a constant dichroic ratio of 1.12 was measured. From this an estimation of the radiation‐induced strain within the lattice was made and found to be ?2×10−2. A new electronic band was found after a long‐term annealing at the wave number 312 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.322334

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Variations of elastic constants and density with strain and the introduction of stresses can significantly affect the propagation velocity of surface acoustic waves. Digital computation using iterative methods is employed to obtain the variations of propagation velocity with strain. It is found that while the individual contributions of the initial stresses, changes in elastic constants, and changes in density with strain can be considerable, their combined effect in some materials may be reduced by mutual cancellation. Computed results forYXquartzYZLiNbO3are compared with experimentally measured values.

ISSN:0021-8979    

DOI:10.1063/1.322293

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The residual‐activity method was employed to evaluate the volume and grain‐boundary diffusion coefficients of mercury in the Ag3Sn alloy at temperatures ranging from 50 to 245 °C. The volume diffusion coefficient obeys the relationshipDv*=1.87×10−5 exp(−8.25×103/RT) cm2/sec. The grain‐boundary diffusion coefficient evaluated from Suzuoka’s exact solution varied from 10−3cm2/sec at 50 °C to 10−1cm2/sec at 245 °C. The large grain‐boundary‐diffusion coefficient was attributed to the increased grain‐boundary width of the alloy caused by the corrosive nature of the mercury.

ISSN:0021-8979    

DOI:10.1063/1.322294

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Loading and unloading of two types of porous beryllium and a porous aluminum under conditions of uniaxial strain, proportional loading, and hydrostatic pressure indicate that yielding is dominated by porosity. Analysis of the data prior to yielding indicates that aspherical pores cause increased compressibility on initial loading. All materials exhibit enhanced compaction when loaded under nonhydrostatic stress conditions. Models which treat the collapse of spherical pores do not agree with the beryllium data, probably because of the influence of aspherical pores and pore‐size distribution.

ISSN:0021-8979    

DOI:10.1063/1.322295

出版商:AIP    

年代:1976

数据来源: AIP