Showing papers by "Sandia National Laboratories published in 1970"

Finite difference methods of solution of the boundary-layer equations

Abstract: multi component diffusion coefficient, ft/sec binary diffusion coefficient, ft/sec thermal diffusion coefficient, Ib sec/ft enthalpy, z^ h^Ci, ft/sec i enthalpy of species i, ft/sec thermal conductivity of mixture, lb/(sec° R) density-viscosity product, piJL/(pn)r multi component Lewis-Semenov number, Cpp binary Lewis-Semenov number Cpp^a/k thermal Lewis-Semenov number, cpDi/k molecular weight of the mixture, 1 / ( Z-j Ci/

Thermoelastic Theory of Stressed Crystals and Higher-Order Elastic Constants

Abstract: Publisher Summary This chapter presents the general theory of thermoelasticity of stressed solids to apply the theory to the interpretation of experiments, which measure nonlinear thermoelastic properties of solids, and to illustrate this application by working out some examples. Experimental work has been motivated by the development in recent years of the measurement of ultrasonic wave velocities as functions of stresses applied to the sample, and the measurement of the amplitude of the first harmonic generated by the passage of an ultrasonic fundamental wave through the sample. These experiments, and others such as the generation of sum- and difference-frequency waves by the interaction of two ultrasonic waves, are all interpreted from the same theoretical basis, namely nonlinear thermoelasticity of anisotropic solids. As thermoelasticity is characterized by a rather cumbersome notation, and indeed throughout the years by many different sets of such notation, corresponding to different theoretical and experimental situations, it is worthwhile to set out the general theory in a unified notation, suitable for application to all experiments on nonlinear thermoelasticity.

Pressure and Temperature Dependence of the Dielectric Properties and Phase Transitions of the Antiferroelectric Perovskites: PbZr O 3 and PbHf O 3

Abstract: Hydrostatic-pressure measurements have shown that in PbZr${\mathrm{O}}_{3}$ the antiferroelectric (AFE)-paraelectric (PE) transition temperature ${T}_{a}$ increases ($\frac{d{T}_{a}}{\mathrm{dP}}=4.5\ifmmode\pm\else\textpm\fi{}0.3\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}/\mathrm{kbar}$) whereas the extrapolated Curie-Weiss temperature ${T}_{0}$ decreases $\frac{d{T}_{0}}{\mathrm{dP}}=\ensuremath{-}16.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}/\mathrm{kbar}$ with increasing pressure. Interpreted in terms of the lattice dynamics, the results give the first experimental evidence that there are two independent low-frequency temperature-dependent lattice vibrational modes in PbZr${\mathrm{O}}_{3}$: a ferroelectric (FE) mode which determines the large polarizability and the Curie-Weiss behavior of the static dielectric constant in the paraelectric phase, and an AFE mode (probably a coupled mode) which causes the AFE transition. On cooling, the crystal becomes unstable against the AFE mode at ${T}_{a}$ just before the instability due to the FE mode is reached at ${T}_{0}$. Pressure increases the frequency of the FE mode but decreases ("softens") that of the AFE mode, and consequently, the static-dielectric-constant anomaly at the transition decreases sharply. The behavior of PbHf${\mathrm{O}}_{3}$ is qualitatively similar to that of PbZr${\mathrm{O}}_{3}$, but is complicated by the presence of two AFE phases at 1 bar. A third AFE phase becomes stable at high pressure. All the AFE transition temperatures increase with pressure, corresponding to the softening of their respective AFE modes. A brief discussion of the nature of the AFE mode in PbZr${\mathrm{O}}_{3}$ is given.

Exchange Striction Effects in MnO and MnS

Abstract: Lattice constants of MnO and MnS have been measured as a function of temperature from 7 to 300\ifmmode^\circ\else\textdegree\fi{}K Below the N\'eel temperature, the fcc lattices undergo a trigonal distortion as well as a volume contraction By subtracting the usual thermal expansion from this volume contraction, the isotropic exchange striction has been studied For MnO below the N\'eel temperature (${T}_{N}\ensuremath{\cong}118\ifmmode^\circ\else\textdegree\fi{}$K), good agreement with the randomphase Green's-function theory previously developed to describe sublattice magnetization is obtained for the trigonal distortion; on the other hand, for the volume contraction, there are no theoretical results available for the region immediately below the N\'eel temperature to compare with the experimental next-nearest-neighbor spin-correlation curve which has been obtained For MnS, below ${T}_{N}(\ensuremath{\cong}147\ifmmode^\circ\else\textdegree\fi{}\mathrm{K})$ the observed trigonal distortion was found to be a contraction along the [111] direction; the magnetization curves suggest, but do not positively prove, the absence of a biquadratic-exchange effect

K -Shell Auger Transition Rates and Fluorescence Yields for Elements Ar-Xe

Abstract: We use calculated Auger and radiative transition rates to compute $K$-shell fluorescence yields for $18\ensuremath{\le}Z\ensuremath{\le}54$. The calculated fluorescence yields are generally higher than the most recent measurements (by as much as 8%). In addition we compare the calculated Auger rates with measured $\mathrm{KLL}$ and $\mathrm{KLM}$ intensities, the calculated $\mathrm{KLL}$ total yield with other calculations, and the calculated $\frac{\mathrm{KLX}}{\mathrm{KLL}}$ and $\frac{\mathrm{KXY}}{\mathrm{KLL}}$ ratios with measurements.

Propagation of steady shock waves in polymethyl methacrylate

Abstract: The particle-velocity histories associated with the compression waves produced by the planar impact of polymethyl methacrylate plates were observed by means of laser interferometry The impact velocity and the thickness of material through which the wave passed were varied from 006 to 064 mm μsec and from 6 to 37 mm respectively Over this range of impact velocities, the observations disclosed a shock followed by a smooth transition to the maximum particle-velocity; the speed and magnitude of the shock varied non-linearly with the impact stress For impact velocities below 03 mm μsec , the wave was steady A steady-wave analysis based on finite linear viscoelasticity theory has been shown to be in good agreement with the experimental observations

Orbital Paramagnetism of Localized Nonmagnetic Impurities in Metals

Abstract: The importance of orbital paramagnetism in a weakly exchange-enhanced dilute solution of transition-metal impurities in a nonmagnetic host metal is demonstrated both theoretically and experimentally It is shown that the orbital and spin contributions to the nuclear resonance shift and relaxation rate separately satisfy a Korringa-like relation These relations may be used to determine uniquely the individual contributions The sensitivity of the analysis to crystal-field effects is discussed

Effects of Co 60 Gamma Irradiation on Epitaxial GaAs Laser Diodes

Abstract: The characteristics of defects introduced in epitaxial GaAs by room-temperature ${\mathrm{Co}}^{60}$ irradiation have been studied by observing the degradation of light emission from GaAs laser diodes. The luminescence degradation is indicative of a decrease in electron lifetime in the $p$-type region brought about by the introduction of nonradiative recombination centers. These defects anneal in a single stage centered at 237\ifmmode^\circ\else\textdegree\fi{}C. Isothermal-annealing studies show that the defects anneal by a first-order kinetic process with an activation energy of 1.7 eV and a preexponential factor of ${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The annealing properties of the defect suggest that it is a complex whose dissociation is the limiting step in the recovery process. The defects can also anneal at temperatures as low as 76\ifmmode^\circ\else\textdegree\fi{}K under the influence of a strong forward bias. A dc forward bias at 2.2\ifmmode\times\else\texttimes\fi{}${10}^{2}$ A/${\mathrm{cm}}^{2}$ at room temperature for 1 h produces complete recovery of the light intensity. The possibility of annealing due to heating while under strong forward bias has been considered and does not appear to be responsible for the bias annealing. Rather, the forward-bias-induced recovery is thought to be due to an increase in the probability of annihilation because of a change in charge state of the defect complex following capture of a minority carrier. The various aspects of forward-bias annealing observed in this study can be explained by this model. On the basis of the above results, the complex has been tentatively identified as consisting of an impurity and an As interstitial.

INFRARED STUDIES OF THE CRYSTALLINITY OF ION-IMPLANTED Si.

Abstract: The crystallinity of ion-implanted silicon has been investigated using ion mass and ion fluence dependences of divacancy formation as measured by the characteristic 1.8 μ absorption band. Room temperature, nonchanneled implants of 400-keV B11, Zn64, and Sb121 ions were performed to maximum fluences of 1014 ions/crn2 for Sb and Zn and to 2 × 1015 ions/cm2 for B. The results are interpreted on the basis of ion energy spent in atomic processes per unit volume, e, within the implanted layer. For e ≤ 1019 keV/cm3 the energy to form a divacancy (1.5 ± 0.5 keV) is nearly ion independent. Maxima appear in the divacancy densities at ∼1013 Sb ions/cm2 and ∼2 × 1013 Zn ions/cm2 where e ≤ 1020 keV/cm3. The divacancy density for B implantation did not exhibit a distinct maximum at E = 1020 keV/cm3, but continued to increase with fluence. The B results are attributed to defect motion because divacancies are observed beyond the calculated depth for energy deposition after a high fluence B implant. In addition t...

Reversible Inhibition of Spore Germination by Alcohols

Abstract: Low levels of alcohols have been found to inhibit the process of spore germination. The extent of germination is dependent upon the concentration of alcohol present in the germinating medium. This inhibition is reversible since removal of the alcohol from the spore environment allows germination to proceed.

On second sound in materials with memory

Abstract: Vor kurzem haben Gurtin und Pipkin eine allgemeine nichtlineare Theorie der Warmeleitung entwickelt, die vollstandig mit den Gesetzen der Thermodynamik vereinbar ist und in welcher Warmestorungen sich mit endlicher Geschwindigkeit ausbreiten. Wir erweitern hier diese Theorie auf verformbare Korper.

Prediction of electron density in the boundary layer on entry vehicles with ablation

Abstract: Computer code for numerical solution of laminar boundary layer and thin shock layer equations predicting electron density around reentry vehicle

Elevated-temperature elastic moduli of 2024 aluminum obtained by a laser-pulse technique

Abstract: Elastic waves were generated in slender polycrystalline 2024 aluminum rods by the deposition of laser energy into the ends of the rods with a Q-switched laser. The propagation velocities of the waves were measured in the temperature range of 22° to 500°C. The elastic moduli of the material determined from these wave-propagation measurements are compared with previously reported single-crystal and polycrystalline aluminum data at elevated temperatures. Elastic moduli for polycrystalline 2024 aluminum agree with other reported data below about 200°C. Above this temperature, the 2024 aluminum moduli were found to decrease more rapidly with temperature than did those for single-crystal aluminum, although not as drastically as has been previously reported for polycrystalline aluminum.

Electron Paramagnetic Resonance of the Aluminum Interstitial in Silicon

Abstract: Electron-paramagnetic-resonance spectra of the ${\mathrm{Al}}^{++}$ interstitial (Si-$G18$) produced in aluminum-doped ($p$-type) silicon by room temperature or 4\ifmmode^\circ\else\textdegree\fi{}K electron irradiations are presented and show that the ${\mathrm{Al}}^{++}$ is located in the tetrahedral interstitial site. The hyperfine interactions with the ${\mathrm{Al}}^{27}$ and surrounding ${\mathrm{Si}}^{29}$ atoms indicate that the wave function for the paramagnetic electron is localized mostly within \ensuremath{\sim}5 \AA{} of the ${\mathrm{Al}}^{++}$ and that within this region the surrounding lattice has ${T}_{d}$ symmetry. From a qualitative description of this wave function in terms of a molecular orbital, an attempt has been made to assign the ${\mathrm{Si}}^{29}$ superhyperfine lines observed in the Si-$G18$ spectrum to particular lattice sites. The ground-state energy level for this paramagnetic electron is on or below the substitutional aluminum acceptor level. From energy arguments, it appears that this electron is in a localized resonant state within the valence band or in a bound state in the band gap below the bottom of the valence band.

ESR of TMPD–TCNQ: Spin Excitations of the Heisenberg Regular Linear Chain

Abstract: The detailed electron spin resonance of single crystals of the charge‐transfer complex tetramethylphenylenediamine–tetracyanoquinodimethan (TMPD–TCNQ) at X band and Q band are reported. The ESR spectra are interpreted as resulting from the thermally excited (activation energy, 0.068 eV) spin excitations of the Heisenberg regular antiferromagnetically coupled chain. Although the exact solution to the excited states of the Heisenberg chain with antiferromagnetic coupling is not available, an approximate solution treating the quasiparticles as Wannier spin excitons is very successful at predicting the spin resonance properties of the excitations; fundamental to the Wannier spin exciton model is the absence of spin correlation in the excitations. The spin–spin (T2−1) and spin–lattice (T1−1) relaxation rates are observed as functions of temperature and are determined mainly by spin exchange between excitons. Exchange is proportional to exciton concentration, and the low activation energy in TMPD–TCNQ allows ex...

Thermal and Sample-Size Effects on the Fluorescence Lifetime and Energy Transfer in Tetracene-Doped Anthracene

Abstract: The fluorescence decay time of anthracene crystals was studied for crystals of various sizes at numerous temperatures between 4.2 and 300 \ifmmode^\circ\else\textdegree\fi{}K. The decrease in the lifetime observed between 300 and \ensuremath{\sim} 140 \ifmmode^\circ\else\textdegree\fi{}K is attributed to changes in the amount of reabsorption, while the decrease observed between \ensuremath{\sim} 75 and 25 \ifmmode^\circ\else\textdegree\fi{}K is consistent with fluorescence emission from two types of levels with different intrinsic lifetimes whose populations are in thermal equilibrium. The time evolution of the anthracene and tetracene fluorescence intensities was also investigated for samples of various sizes and at numerous temperatures. The results cannot be explained by exciton diffusion theory and are consistent with the predictions of long-range-interaction theory only if an anomalously large value is assumed for the strength of the interaction. This discrepancy is not yet understood, but it is shown that it is not due to the effects of reabsorption.

Room-temperature adsorption of oxygen on tungsten surfaces: A review

Abstract: Room-temperature adsorption of oxygen on tungsten surfaces is reviewed. Emphasis is on the adsorption features obtained from modern, experimental studies of polycrystalline and monocrystalline samples. Adsorption features discussed include coverage, sticking coefficient, adsorption states, work function change, and electron impact desorption cross sections. Possible reasons for disagreement on these adsorption features and some criteria for reproducible results are presented.

Thermodynamics of formation of Th-Co alloys

Abstract: Electromotive force cells have been used to determine the Gibbs free energies, enthalpies, and entropies of formation for Th2Coi7, ThCo5, Th2Co7, ThCo, and Th7Co3. Solid CaF2 was employed as the electrolyte, and measurements were made over the temperature range 917‡ to 1233‡K. Comparison of the Th-Co enthalpy values with Th-Ni values shows that the relative bond strengths associated with thorium-transition metal interactions in the two systems invert between the thorium-poor and thorium-rich regions.

Angular Distribution of Protons from Collisional Dissociation of H 2 + . II. Vibrational Dissociation

Abstract: A classical-impulse binary-collision model is used to predict the laboratory angle and velocity distributions of protons resulting from the vibrational dissociation of ${\mathrm{H}}_{2}^{+}$ by He. The treatment is partly heuristic and is not a quantitative success, since the computed cross sections turn out to be roughly an order of magnitude too large compared to those for electronic excitation of the $2p{\ensuremath{\sigma}}_{u}$ state of ${\mathrm{H}}_{2}^{+}$. Nonetheless, the theory clearly identifies some major features of the experimental results of Gibson, Los, and Schopman as being due to vibrational dissociation.