Showing papers on "Atmospheric temperature range published in 1969"

Temperature Dependence of Ms and K1 of BaFe12O19 and SrFe12O19 Single Crystals

Abstract: Single crystals of BaFe12O19 and SrFe12O19 were grown in a Na2O flux. Static magnetic measurements on the two crystal types were made to reveal Ms and K1 as functions of temperature. It was found that Ms of BaFe12O19 and SrFe12O19 are practically identical over the temperature range 77°K to the Curie point with a room‐temperature value of 380 G. Extrapolations to absolute zero reveal that the Bohr magneton numbers are approximately 19.3 and 19.7 per molecule, respectively, while the Curie points are 740° and 750°K, respectively, for BaFe12O19 and SrFe12O19. K1 for SrFe12O19 is 10% higher than that of BaFe12O19 over the entire temperature range. Room temperature values are 3.25×106 and 3.57×106 erg/cc, respectively, for BaFe12O19 and SrFe12O19. Calculations made on the basis of the Stoner‐Wohlfarth theory indicate that the intrinsic coercive force of SrFe12O19 will be higher than that of BeFe12O19 by about 10%. Theoretical room‐temperature values of coercive force for an isotropic assembly of crystallites ...

Tunneling, Zero-Bias Anomalies, and Small Superconductors

Abstract: We have prepared tunnel junctions which contain small Sn particles imbedded in the oxide barrier. The size distribution of the small particles has been determined from electron micrographs. The electrical characteristics of these junctions were measured in the temperature range 1-300\ifmmode^\circ\else\textdegree\fi{}K and in magnetic fields up to 100 kOe. All junctions show a large temperature-dependent resistance peak at zero bias and at low temperatures. The resistance peak increases in magnitude when the Sn particles are made superconducting. A simple model based upon the capacitance of the particles can account quantitatively for this behavior. We believe that a simple extension of this model can account for at least some of the previously reported zero-bias resistance anomalies. From the experiment, it is also possible to extract information about the superconductivity of small particles. We find that Sn particles down to at least a radius $r\ensuremath{\sim}25$ \AA{} are superconducting. The transition temperature of the particles increases with decreasing particle size and reaches 4.2\ifmmode^\circ\else\textdegree\fi{}K for particles with $r\ensuremath{\sim}70$ \AA{}, compared with ${T}_{c}=3.7\ifmmode^\circ\else\textdegree\fi{}$K for bulk Sn. In the radius range $rg100$ \AA{}, the critical field of the particles can be described in terms of a theory by De Gennes and Tinkham. Smaller particles have a much higher critical field, which increases more rapidly with decreasing radius than predicted by that theory.

Yielding and fracture in tungsten and tungsten-rhenium alloys

Abstract: A study was made of the mechanical properties of vacuum arc-melted tungsten and tungsten-rhenium alloys in the temperature range 77 °–810 °K in order to elucidate the mechanism by which rhenium additions lower the ductile-brittle transition temperature of tungsten. The temperature and strain rate dependency of the yield stress of tungsten are reduced by alloying with rhenium, inferring a reduction in the Peierls stress. The reduction in the transition temperature is attributed to the reduced Peierls stress through its effect on the mobility and rate of multiplication of dislocations.

Temperature and Alloy Compositional Dependences of the Energy Gap of Hg1−xCdxTe

Abstract: The temperature and compositional dependences of the energy gap are determined for the alloy semiconductor mercury‐cadmium telluride (Hg1−xCdxTe). The cutoff wavelength was measured on photoconductive and photovoltaic infrared detectors where 0.17

Studies of the ionic ferromagnet (LaPb)MnO3 III. Ferromagnetic resonance studies

Abstract: Ferromagnetic resonance has been observed in single crystals of the family La1−xPbxMnO3with 0.25 < x < 0.45 from 13 to 25 GHz and in the temperature range from 77 to 430 °K. The line width, ΔH, exh...

Thermal expansion of yttrium and gadolinium iron, gallium and aluminum garnets

Abstract: Lattice constants of yttrium and gadolinium iron and gallium garnets and of yttrium aluminium garnet have been measured in the temperature range 296–1400°K. The results show that among these, GdGaG gives the closest match of Δa/a0 vs. T to YIG and to GdIG.

The optical properties of copper and gold as a function of temperature

Abstract: The optical absorption spectra of copper and of gold have been measured polarimetrically as a function of temperature, while in ultra-high vacuum. The copper spectrum was obtained from 17-59 eV over the temperature range 77-920 °K and that of gold from 05-59 eV over the temperature range 295-770 °K. The main absorption peaks of both metals were found to vary with temperature and by comparison with calculations for the band structure of copper for various lattice parameters it was possible to identify peak positions with the following transitions: for copper, X5 -> X4prime at 397 eV, L2prime -> L1u at 478 eV and L11 -> EF(L2prime) at 532 eV, for gold L2prime -> L1u at 408 eV and X5 -> X4prime at 455 eV.

Specific Heat and Heat of Crystallization of Amorphous Germanium

Abstract: : The specific heat and heat of crystallization of vapor- and electro-deposited amorphous germanium were measured with a differential scanning calorimeter. The excess specific heat of the amorphous germanium over that of crystalline phase increased linearly with temperature over the temperature range from 215 to 460K. The heat of crystallization of the amorphous films was found to be about 2.75 k cal/gm-atom. The interpretation of the results in terms of the structure is discussed. The specific heat of crystalline germanium was also measured for the temperature range from 215 to 700K. (Author)

Study of Localized Levels in Semi-Insulators by Combined Measurements of Thermally Activated Ohmic and Space-Charge-Limited Conduction

Abstract: It is shown that measurement of thermal activation energies for both Ohmic and space-charge-limited conduction over a broad temperature range enables the deduction of both depth and concentration of localized levels in a semi-insulator, while measurement of the activation energy for Ohmic conduction alone is rarely definitive for a wide band-gap material. The basis for interpreting thermal activation energies for electrical conduction is discussed in detail. The analysis is applied to recent results on HgS, GaP, CdS, and ZnS: Cd.

Precipitate strengthening mechanisms in magnesium zinc alloy single crystals

Abstract: The mechanical behaviour of Mg-5.1 wt % Zn alloy single crystals was studied in the 4.2 to 300° K temperature range. Quenched crystals have activation energies and volumes best associated with the cutting of small clusters of Zn atoms by dislocations. Fully hardened crystals contain fine β 1′ and occasionalβ 2′ precipitates with an averageβ 1′ interparticle spacing of 330 to 660 A. Strengthening in these crystals is mainly ascribed to the cutting of β 1′ particles by dislocations. In the overaged condition β 1′, β 2′ and equilibrium β particles are present and lead to a considerable temperature-dependence unusual for an overaged condition. Analysis of this temperature-dependence suggests that below 77° K the relatively easy cutting of β 1′ particles by dislocations takes place in addition to the cutting of β 2′ and β particles. Above 77° K the difficult cutting of β 2′ and β particles alone controls the deformation, β 1′ being more easily cut with the aid of thermal fluctuations.

Pressure and Temperature Dependence of the Acoustic Velocities in Polymethylmethacrylate

Abstract: The acoustic velocities in polymethylmethacrylate have been measured with an ultrasonic pulse‐echo technique as functions of frequency, temperature, and pressure. At atmospheric pressure, data on the velocities and attenuation coefficients were obtained for the temperature range of 22°–75°C in the frequency range of 6–30 MHz. For the measurements of velocity and attenuation as a function of frequency, the complex adiabatic bulk modulus was calculated at room temperature and atmospheric pressure for the above frequencies. At temperatures of 25°, 40°, 55°, and 75°C, the pressure dependence of the longitudinal and shear velocity was determined to 150 kpsi at a frequency of 6 MHz. It was found that the measured velocities under increasing pressure conditions were generally lower than those of decreasing pressure by about 0.5% for the longitudinal measurements and about 1% for the shear measurements. However, measurements of the velocities at atmospheric pressure after the specimens had been exposed to 150 kpsi were usually within 0.1% of the initial values. A discussion is presented which compares the continuity of the present data with equation of state determinations in PMMA at elevated pressures.

Elastic properties of polycrystalline TiB2, ZrB2 and HfB2 from room temperature to 1300 °K☆

Abstract: The Young's, shear, and bulk moduli of polycrystalline TiB2, ZrB2, and HfB2 were determined from 298 ° to 1300 °K by the sonic resonance technique. All three of these moduli decreased by about 9% over the temperature range considered. The Young's and shear moduli were fitted to Wachtman's empirical equation. The theoretical Soga-Anderson equation was applied to the bulk modulus-temperature data and found to fit the data within 1% despite the variation of the Soga-Anderson constant, δ, with temperature. The Gruneisen constant, γ, was found to remain invariant with temperature while the Poisson's ratio increased with increasing temperature. Debye temperatures were computed from the measured Young's and shear moduli.

Examination of the Adequacy of the 12–6 Potential for Liquid Argon by Means of Monte Carlo Calculations

Abstract: Monte Carlo calculations of thermodynamic properties of argon are reported for the temperature range between the triple point and the critical temperature at pressures up to 700 atm. It is shown that the Lennard‐Jones 12–6 potential with the parameters proposed by Michels et al., viz., e / k = 119.8°K and σ = 3.405 A, leads to internal energies and pressures which are in fair agreement with the experimental values. The over‐all agreement with experiment may be substantially improved by reducing the depth of the potential well to e / k = 117.2°K. The use of other potentials, the importance of nonadditivity corrections, and the agreement between the Monte Carlo results and those obtained by the method of molecular dynamics are briefly discussed.

Thermal Cycling and Surface Reconstruction in Aluminum Thin Films

Abstract: The appearance of "annealing hillocks" on heat treated aluminum films has been previously reported Thin films of Al, deposited on passivated wafers, were annealed for various lengths of time in the temperature range 200°–500°C The effects of grain size, alloying and surface passivation on hillock formation, were studied It is the purpose of this report to summarize the effect of thermal cycling on similar films and to show in more detail the size and appearance of the hillocks Aluminum was deposited on oxidized silicon substrates in a vacuum of about 10−8 Torr Grain sizes at the deposition temperature were on the order of <1μ, 1μ, and 5μ Manual cycling was carried out between a hot stage in N2 and a room temperature heat sink Control samples were annealed (uncycled) for equivalent times‐at‐temperature Photomicrographs of the surface at its various stages of reconstruction were taken and scanning electron micrographs provided a more detailed view of individual hillocks and their surroundings At the higher temperatures (425°C) thermal cycling increases the number of hillocks by factors of 2 or 3, with the typical hillock density estimated to be approximately 106/cm2 Cycling also increases the size of the protrusions, and hillocks as high as 35μ have been observed growing out of a 07μ film Experiments employing glass passivation confirm earlier results that surface reconstruction can be eliminated

Excimer Fluorescence of Benzene and Its Alkyl Derivatives—Concentration and Temperature Dependence

Abstract: Fluorescence spectra and quantum yields have been obtained for methylcyclohexane solutions of benzene, toluene, ethylbenzene, cumene, p‐, m‐, o‐xylene, and 1,3,5‐, 1,2,3‐, 1,2,4‐trimethylbenzene as a function of aromatic concentration over the temperature range from 25 to −100°C. At low temperatures distinct excimer emissions were observed for all compounds studied. The intrinsic emission quantum yields of monomer φm and of excimer φe have been determined by a simple technique which requires no assumptions regarding the details of the monomer–excimer kinetics. With decreasing temperature, φe is observed to decrease contrary to the behavior of φm, suggesting that the rate constant for the excimer radiative transition decreases strongly as the temperature is lowered. Such temperature dependence is explained as arising from the existence of a substantial vibronic component in the transition moment that is induced by thermal excitation of upper‐state vibrational motions (e.g., torsional, tilting, etc.) of one...

The Interactions of Point Defects with Impurities in Silicon

Abstract: The minority carrier lifetime in gamma-irradiated silicon crystals was studied. In F. Z. n type crystals containing phosphorous, arsenic, antimony or bismuth, there are two annealing stages in the temperature range 100–280°C and in both stages there is strong dependency of activation energies E a and frequency factors on the atomic size of the impurity. The relationship between E a and covalent radii of the impurity atom can be experimentally expressed in linear functions. The defect which anneals in the lower temperature stage is a complex of donor atoms associated with a vacancy type defect. Si-E center anneals in the higher temperature stage and the values of activation energies completely agree with those obtained by Watkins et al. in their experiments of reorientation of donor-vacancy axis. The defects of both stages are considered to migrate to the sinks of oxygen after jumps of about 10 5 . It is very interesting to note that this study shows only one example of an impurity atom which moves with a ...

High-temperature sulfur corrosion of iron-chromium alloys

Abstract: The kinetics and the mechanism of sulfurization of Fe-Cr alloys containing from 0.35 to 74 at. % Cr were studied in the temperature range 700–1000°C. The sulfurization was conducted in sulfur vapor at atmospheric pressure. The reaction rate was determined by the continuous gravimetric method. The scale composition was studied by X-ray and electron microprobe methods. The contribution of the reactants to the process of material transport through the scale was examined with both the marker method and the autoradiographic method using the radioactive isotope35S. It has been found that, irrespective of alloy composition and temperature, the sulfurization follows a parabolic rate law. On the dilute alloys (up to about 2 at. % Cr) the scales formed are monophase consisting of Fe1−xS only. In the range 2–40 at. % Cr the scale is a heterophase mixture of Fe1−xS and the mixed spinel FeFe2−xCrxS4. On the chromium-rich alloys the scale is monophase and is built of a solid solution of FeS in Cr2S3. The scale growth on the alloys under examination proceeds without the participation of the inward diffusion of sulfur. The mechanism of the scale formation has been proposed.

Properties of Neodymium Laser Materials

Abstract: The optical properties of neodymium-doped crystalline and glass laser materials have been studied in an attempt to further the development of laser materials (emitting at 1.06 μ) for specific applications. The 1.06-μ fluorescence lifetimes and relative fluorescence conversion efficiencies for the more promising materials such as YAG:Nd and glass: Nd have been measured over the temperature range 300–500 K. Also determined were the effects of sensitization of YAG:Nd by Cr3+ (the enhancement of 1.06-μ fluorescence and the Cr3+ → Nd3+ energy transfer times). Further absorption spectra and fluorescence lifetimes have been determined for a large group of crystalline and glass laser media under room temperature conditions. The study of these optical properties and their thermal dependences in this temperature region provide information that is useful in solving laser device problems such as optimization of operating temperature and of pump characteristics. Presented in this paper are the results obtained from the above experimental study of the optical properties together with a collection of data from the literature of optical, thermal, and physical properties of these laser materials.

Electrical Properties of Semiconducting Cd F 2 :Y

Abstract: Measurements of resistivity and the Hall coefficient in the temperature range 425-4.2\ifmmode^\circ\else\textdegree\fi{}K have been made on single crystals of semiconducting Cd${\mathrm{F}}_{2}$ doped with yttrium (Y). The Y concentrations ranged from 0.002-1 mole%. The characteristic behavior of impurity-band conduction is observed, with the activation energies ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, and ${\ensuremath{\epsilon}}_{3}$. The onset of impurity-band conduction occurs at higher temperatures than in other semiconductors. No degeneracy effects are seen for the highest concentrations observed. The data are analyzed on the basis of simple semiconductor theory, assuming a hydrogenic nature of the Y donor. Using the value of effective polaron mass ${m}_{p}\ensuremath{\approx}0.9{m}_{e}$ and the static dielectric constant ${\ensuremath{\epsilon}}_{0}=8.1$, we find that the calculated ionization energy is larger than the experimental value. The impurity-banding behavior cannot be characterized in a fashion similar to what has been done in other semiconductors. Alternative analyses are suggested. The Hall coefficient is analyzed on the basis of the two-band model: the conduction band and the impurity band. At temperatures above 250\ifmmode^\circ\else\textdegree\fi{}K, the Hall-mobility data can be fitted by assuming polar optical mode and an acoustic mode as the dominant scattering mechanisms. The deformation potential was found to be 8.2\ifmmode\pm\else\textpm\fi{}1 eV. Below 250\ifmmode^\circ\else\textdegree\fi{}K, ionized impurity-scattering is the additional mechanism. At temperatures below \ensuremath{\sim}80\ifmmode^\circ\else\textdegree\fi{}K, the mobility falls off sharply owing to impurity banding.

Young's modulus and secondary mechanical dispersions in polypromellitimide

Abstract: Dynamic mechanical properties were determined in polypyromellitimide at acoustic frequencies over a wide temperature range (80–750°K). Two distinct secondary relaxation effects were found: one (β′) at lower temperature, characterized by a loss maximum at 250°K, and another (β) at higher temperatures with a loss maximum at 400°K. The lower temperature peak is shifted towards higher temperature with increasing frequency following an Arrhenius-type equation (apparent activation energy: 15 kcal/mole); the relaxation strength increases with water content and becomes practically zero when samples dried under vacuum at 200°C are examined. The β′ relaxation process is thus attributed to the presence of adsorbed water molecules. The higher-temperature (β) dispersion, which persists even after dehydration, on the basis of some results obtained for other polymers containing p-oxylphenylene rings in the backbone, is tentatively attributed to torsional oscillations of aromatic rings along the chain.

Thermal Expansion of Fused Quartz

Abstract: Results of a series of observations on the linear thermal expansion coefficient of transparent fused quartz are given in the temperature range of 300 °C to 1065°C, with particular attention being given to the region of 1000 °C. The experiments are carried out by the comparator method. The ten specimens, which could conveniently be classified into three types, were supplied by the Thermal Syndicate Ltd., England and by three manufacturers, the Toshiba Ceramics Ltd., the Nippon Sekiei Garasu Ltd. and the Kimmon Manufacturing Ltd., in Japan. Different value is obtained in thermal expansion of the specimens each type for which an empirical formula is given.