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Showing papers on "Atmospheric temperature range published in 1989"


Patent
27 Jun 1989
TL;DR: In this paper, a thin film of shape-memory material, such as nickel titanium (Ni-Ti), is applied to a substrate and annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cooling down rate to produce on ordered, partially disordered or fully disordered BCC structure.
Abstract: A method of producing an integral piece of thermo-sensitive material, which is responsive to a shift in temperature from below to above a phase transformation temperature range to alter the material's condition to a shape-memory condition and move from one position to another. The method is characterized by depositing a thin film of shape-memory material (11 and 12), such as nickel titanium (Ni-Ti) onto a substrate (10) by vacuum deposition process such that the alloy exhibits an amorphous non-crystalline structure. The coated substrate is then annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce on ordered, partially disordered or fully disordered BCC structure. Also disclosed are actuator devices employing 'shape-memory material' (1) actuators.

285 citations


Journal ArticleDOI
01 Sep 1989
TL;DR: In this article, the authors measured the temperature dependence of the adiabatic elastic moduli of single-crystal MgO over the temperature range 300-1800 K. The high temperature limit of their measurements extends by 500 K the upper limit over which elasticity data on MgOs are now available.
Abstract: Using the rectangular parallelepiped resonance method we measured the temperature dependence of the adiabatic elastic moduli of single-crystal MgO over the temperature range 300–1800 K. The high temperature limit of our measurements extends by 500 K the upper limit over which elasticity data on MgO are now available. Although our measured temperature dependence of C ij s are generally in good agreement with previous measurements over a more narrow range in temperature, we found that C 44 s decreases more rapidly with temperature, for T > 1000 K, than previous studies suggest. We also found that each of the slopes (ϱC 11 s /ϱT)p, (ϱKs/ϱT)p, and (C 44 s /ϱT)p become less negative with increasing temperature for T > 1400 K. From our measurements on elasticity we are able to confirm that the Gruneisen parameter at zero pressure is nearly constant with temperature up to 1800 K, with only a slight decrease above 1000 K. Utilizing our new data we present calculations showing the temperature dependence of thermodynamic parameters important in studies of earth's interior.

252 citations


Journal ArticleDOI
TL;DR: In this article, the La1−xSrxMnO3 (0 ≤ x ≤ 0.5) system has been characterized by X-ray diffraction, thermal and electrochemical analysis.

250 citations


Journal ArticleDOI
TL;DR: In this paper, the nine adiabatic elastic constants of single-crystal forsterite are reported for the temperature range 300-1700 K at ambient pressure, and the resulting Hill-averaged bulk and rigidity moduli Ks and G are lower at 1700 K than predicted by linear extrapolation of low-temperature data.
Abstract: Measurements of the nine adiabatic elastic constants of single-crystal forsterite are reported for the temperature range 300–1700 K at ambient pressure. The measured room temperature Cijs and their first temperature derivatives at ambient conditions are generally consistent with previous measurements, which were taken over a narrower temperature range. Slight nonlinear behavior is observed in the temperature dependence of the C11s, C22s, and C33s moduli. The resulting Hill-averaged bulk and rigidity moduli Ks and G are lower at 1700 K than predicted by linear extrapolation of low-temperature data. At 1700 K the new data give Ks = 103.8 ± 1.1 GPa and G = 61.3 ± 0.5 GPa. Isotropic elastic wave velocities have been calculated using the Hill averaging scheme over the range of temperatures measured. At T = 1700 K and ambient pressure we find vp = 7.79 ± 0.04 km s−1 and vs = 4.48 ± 0.03 km s−1. The parameter (∂lnvs/∂lnvp)P is near to 1.2 and independent of temperature. Calculations are presented for elastic properties and other parameters important for the equations of state and anharmonicity of forsterite. Recent high-temperature thermal expansion measurements on a forsterite specimen from the same boule are used in this analysis. Effects of uncertainties in high-temperature thermal expansion data on these parameters have been evaluated and are discussed.

221 citations


Journal ArticleDOI
TL;DR: In this article, a dc bias voltage of +300 V was applied to an interposing ring to reduce the substrate temperature from 650 to 500°C for obtaining epitaxial films, and the thickness of the films varied from 500 to 5000 A with superconducting transition temperatures varying from 87 to 90 K for 650°C deposits.
Abstract: We report the formation of excellent quality epitaxial YBa2Cu3O7 films on (100) SrTiO3 and (100) ZrO2 (yttria stabilized) substrates in the temperature range of 500–650 °C by XECl excimer laser ablation in a 0.2 Torr oxygen ambient. By applying a dc bias voltage of +300 V to an interposing ring, we were able to reduce the substrate temperatures from 650 to 500 °C for obtaining epitaxial films. The quality of the epitaxial films was found to decrease with temperature, particularly below 550 °C. The thickness of the superconducting films was varied from 500 to 5000 A with superconducting transition temperatures Tc (zero resistance) varying from 87 to 90 K for 650 °C deposits. The critical current density Jc of films was found to vary linearly with temperature with values of (zero magnetic field at 77 K) 5.0×106 and 1.0×106 for films deposited at 650 °C on (100) SrTiO3 and (100) yttria‐stabilized zirconia substrates, respectively. X‐ray diffraction, transmission electron microscopy, electron channeling patte...

181 citations


Journal ArticleDOI
TL;DR: In this paper, the three Raman active modes predicted by group theory have been identified and their room temperature frequencies determined to be 298, 345 and 632 cm −1, and a new mode appears in the spectra (240 cm − 1 at 15K) as the sample is cooled below the Neel Temperature (TN = 225± 5k of Cupric Oxide).

174 citations


Journal ArticleDOI
TL;DR: In this article, a single crystal of n -type Bi 2 Te 2..85 Se 0.15 with the composition of a useful thermoelectric cooling material was grown by the Bridgman technique.

159 citations


Journal ArticleDOI
TL;DR: In this paper, a systematic investigation has been carried out on the time and temperature dependence of the electrical conductivity of ZnO films deposited via spray pyrolysis on ceramic substrates in the temperature range 498-573 K in the presence of dispersed Pt as the catalyst.
Abstract: Thick film polycristalline ZnO gas sensors for hydrogen partial pressure determination in hydrogen-air mixtures present at very complex kinetic behavior that demands to be thoroughly clarified in order for them to be used in practical applications. For this reason a systematic investigation has been carried out on the time and temperature dependence of the electrical conductivity of ZnO films deposited via spray pyrolysis on ceramic substrates in the temperature range 498-573 K in the presence of dispersed Pt as the catalyst

159 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature using a thermogravimetric technique in the temperatures range of 1823 to 1948 K.
Abstract: The oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature was investigated using a thermogravimetric technique in the temperatures range of 1823 to 1948 K. The specimens were prepared by chemical vapor deposition using SiCl4, C3H8, and H2 as source gases. The oxidation behavior of the CVD-SiC indicated “passive” oxidation and a two-step parabolic oxidation kinetics over the entire temperature range. The crystallization of the SiO2 film formed may have caused this two-step parabolic behavior. The parabolic oxidation rate constant (Kp) varied with the square root of the oxygen partial pressure (P1/2O2). The activation energy for the oxidation was determined to be 345 and 387 kJ · mol−1. These values suggest that the diffusion process of the oxygen ion which passes through the SiO2 film is rate-controlling.

156 citations


Journal ArticleDOI
TL;DR: This is the first concrete experimental evidence for the temperature-induced magnetic moment of Co ions in this oxide as proposed in the thermally populated high-spin model.
Abstract: Polarized and unpolarized neutron measurements have been performed on ${\mathrm{LaCoO}}_{3}$ in a temperature range between 10 and 295 K. A drastic decrease in the magnetic cross section is observed below 150 K. This is the first concrete experimental evidence for the temperature-induced magnetic moment of Co ions in this oxide as proposed in the thermally populated high-spin model. The temperature dependence of the moment is in qualitative agreement with that calculated from the magnetic-susceptibility data.

146 citations


Journal ArticleDOI
TL;DR: In this paper, the perovskite structured ceramic SrCeO3, doped with Yb3+ and treated in water vapor, was investigated in the temperature range 25-250°C using complex impedance analysis to allow determination of the true bulk conductivity.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the diffusion of water into silica glass in the temperature range of 200° to 750°C by treating the glass in air containing a constant water vapor pressure and analyzing the concentration profile using a Fourier transform infrared spectrometer.
Abstract: Diffusion of water into silica glass was measured in the temperature range of 200{degrees} to 750{degrees}C by treating the glass in air containing a constant water vapor pressure and analyzing the concentration profile using a Fourier transform infrared spectrometer. In the short-time diffusion heat treatments, the surface concentration was lower and the apparent diffusion coefficient was higher than the corresponding steady-state values. The temperature dependence of the steady-state diffusion coefficient showed two different activation energies. Above {approximately}550{degrees}C the diffusion coefficients were similar to the published results with an activation energy of {approximately}80 kJ/mol, while below {approximately}550{degrees}C, the diffusion coefficient was higher than the value obtained by extrapolation from higher temperatures, and the activation energy was {approximately}40kJ/mol. Correspondingly, the water solubility- temperature relation showed a sudden change at around the same temperature: at temperatures above this temperature the solubility increased with decreasing temperature, while at lower temperatures the trend was reversed. It is suggested that this observed peculiarity was caused by the initial nonequilibrium reaction between water and SiO{sub 2} glass and a change in enthalpy of the glass-water reaction.

Journal ArticleDOI
TL;DR: In this article, the vapor pressure of liquid copper (II) hexafluoroacetylacetonate was determined over the temperature range 97°•120°C and the standard enthalpy of evaporation was found to be.
Abstract: Thermally activated decomposition of the vapor phase of copper (II) hexafluoroacetylacetonate was studied. It was found that the temperature at which the decomposition is carried out influences dramatically the chemical composition of deposits; the higher the temperature, the more carbon is incorporated. Pure copper deposits having resistivities of 3–7 μΩ cm were obtained at substrate temperatures of 340°–390°C. It is believed that in this temperature range, breaking of the metal‐ligand bond of the copper compound takes place while at higher temperatures the onset of the ligand decomposition itself becomes significant. The vapor pressure of liquid copper (II) hexafluoroacetylacetonate was determined over the temperature range 97°‐120°C. The standard enthalpy of evaporation was found to be .

Journal ArticleDOI
TL;DR: In this article, the thermochromic effect of poly(3-alkylthiophenes) was investigated and it was shown that the optical absorption shifts to higher photon energies with higher temperature, assuming a change of polymer conformation from rigid rod geometry at low temperatures to a random coil conformation at higher temperatures.

Journal ArticleDOI
TL;DR: In this article, a modification of the Nernst-Lindemann equation was proposed to convert calculated heat capacities at constant pressure to heat capacity at constant volume for solid, linear macromolecules.
Abstract: A modification is proposed for the Nernst-Lindemann equation that is used to convert calculated heat capacities at constant pressure (C p ) to heat capacities at constant volume (C v ) for solid, linear macromolecules. the constant A0 per mole of repeating unit in this equation is derived by taking into account the variable number of vibrators excited at different temperatures. With the new equation it is possible to calculateC p for solid polymers over a wider temperature range. The constant is calculated for solid polymers from experimental thermal expansivity, isothermal compressibility and heat capacity data obtained from the literature. An average value of (3.9±2.4)×10−3(K mol)/J was obtained for A0 (new) from data on 22 solid polymers. This average value may be used as a universal constant in case no experimental data on compressibility and expansivity are available for computation ofA 0. The remaining variation of A0 (new) with temperature is discussed and example calculations are shown for polyethylene. Effects of premelting and possibly large-amplitude motion are discovered for polyethylene in the temperature range 290 to 410 K.

Journal ArticleDOI
TL;DR: In this paper, an analytical diffusion model for multiphase diffusion was used to calculate the diffusion coefficients of nitrogen in the phases of the Ti-TiN system from layer growth experiments, and the temperature dependence of nitrogen diffusion in TiN (δ), Ti2N (e), and α titanium was found to obey the following relations: Dinδ=4.4±1.62 × 10su-5 exp-36,500±1400/RT Dine=2.7± 1.05 ×10su-3 exp-35,760±2500/
Abstract: Pure titanium specimens were ion nitrided in a nitrogen plasma in the temperature range of 800 ‡C to 1080 ‡C at various nitrogen partial pressures. During ion nitriding, titanium nitrides TiN and Tiin2N and nitrogen solid solution layers (α and Β) were formed consistent with the equilibrium phase diagram. The kinetics of growth of these layers were studied as a function temperature and ion-nitriding parameters. An analytical diffusion model for multiphase diffusion was used to calculate the diffusion coefficients of nitrogen in the phases of the Ti-TiN system from layer growth experiments. Using the layer growth data, the temperature dependence of nitrogen diffusion in TiN (δ), Ti2N (e), and α titanium was found to obey the following relations: Dinδ=4.4±1.62 × 10su-5 exp-36,500±1400/RT Dine=2.7±1.05 ×10su-3 exp-35,760±2500/RT Dinα=0.96±0.08 × exp-51,280-505/RT

Journal ArticleDOI
TL;DR: In this article, a rhombohedral perovskite structure of NdNiO{sub 3] has been prepared with a low-temperature method, and its magnetic and electric properties have been studied between 4 and 300 K.

Journal ArticleDOI
TL;DR: In this paper, a strong influence of the transition metal d-band filling Z nd on many properties is inferred from the similarity of the variation of these properties with Znd for the three transition metal rows.

Journal ArticleDOI
TL;DR: In this paper, the authors applied the constant temperature and pressure molecular dynamics technique to the simulation of structural and thermodynamic properties of the MgO crystal in the temperature range between 300 and 2000 K, using empirical pair potential functions consisted of the Coulomb, dispersion, and repulsion interactions.
Abstract: We have applied the constant temperature and pressure molecular dynamics technique to the simulation of structural and thermodynamic properties of the MgO crystal in the temperature range between 300 and 2000 K, using empirical pair potential functions consisted of the Coulomb, dispersion, and repulsion interactions. Quantum corrections are included, based on the Wigner–Kirkwood expansion of the free energy in powers of Planck constant h. In the present study, only the first nonvanishing term with the order h2 is considered. As expected, quantum effects on the properties are found to become increasingly important with decreasing temperature. In view of the simplicity of the potential used, our simulation is quite successful in reproducing a wide range of measured properties of MgO, including the crystal structure, bulk modulus, thermal expansion coefficient, heat capacity, and mean‐square atomic displacements over a wide temperature range above 500 K. However, at lower temperatures, both the heat capacity...

Journal ArticleDOI
TL;DR: In this paper, the activation energies of three different metastable states were evaluated assuming the validity of the Arrhenius law and a first order reaction for the three different types of states.
Abstract: And the decay was measured in the temperature range of 106 K-300 K. All metastable states decay thermally according to an exponential law. We could not observe any emission of radiation in the energy range of 5 eV-0.3 eV during the thermal decay. We have evaluated the activation energies E A and frequency factors Z assuming the validity of the Arrhenius law and a first order reaction for three different metastable states. They all can be completely annihilated with red light. A strong temperature dependence with respect to the generation of the metastable states was observed

Journal ArticleDOI
TL;DR: In this paper, the effect of high pressure up to 12 kbar on thermal conductivity of silicate rocks was determined by the transient hot wire method on 23 samples, with the exception of one sedimentary rock, one meteorite and manufactured fused and crystalline quartz.

Journal ArticleDOI
TL;DR: The half-lives (t1/2) for evaporative loss of n-alkyl andn-alkenyl acetates from rubber septa were determined at temperatures varying from 15 to 35 °C and half-Lives were shown to depend on the vapor pressure of a compound in the formulation substrate, but not on the Vapor pressure of the pure compound.
Abstract: The half-lives (t1/2) for evaporative loss ofn-alkyl andn-alkenyl acetates from rubber septa were determined at temperatures varying from 15 to 35 °C. The changes int1/2 with temperature gave high correlations with the equation, Int1/2 = ΔH/RT+yo where ΔΔH is the heat of vaporization,R is the gas constant,T is the absolute temperature, andyo is a constant. Half-lives changed dramatically with temperature and the degree of change with temperature increased with increasing molecular weight. For mixtures, component ratios changed with temperature, but the degree was modest. At 20 °C there was a 7.5-fold ratio oft1/2 between members of the homologousn-alkyl orn-alkenyl acetates differing by two carbon atoms. The large change int1/2 with temperature and with number of carbon atoms is a consequence of the thermodynamic relationships and the temperature range of pheromone usage. Therefore, a similar degree of change inf1/2 with temperature and number of carbon atoms will apply to other formulations of the same type (those in which the rate of evaporation is first order). The values oft1/2 at 20 °C mainly agreed very well with those reported previously at room temperature. However, our previously reported values for pentadecyl and hexadecyl acetate were revised. Half-lives were shown to depend on the vapor pressure of a compound in the formulation substrate, but not on the vapor pressure of the pure compound.

Journal ArticleDOI
TL;DR: The shrinkage rates of small prismatic dislocation loops in thin foils of sapphire (α-Al2O3) have been determined using transmission electron microscopy.
Abstract: The shrinkage rates of small prismatic dislocation loops in thin foils of sapphire (α-Al2O3) have been determined using transmission electron microscopy; between observations the thin foils were annealed ex situ in the temperature range 1200° < T < 1500°C. The shrinkage rates of individual loops were used to determine the diffusivity of the rate-controlling species, assumed to be oxygen. The loop annealing results agree well with an extrapolation of oxygen self-diffusion data for undoped crystals obtained by conventional tracer techniques in the temperature range 1400° < T < 1900°C. The oxygen diffusion rate was slower in 600-ppm-Ti-doped and faster in 250-ppm-Mg-doped crystals compared to undoped sapphire, consistent at first sight with a “classical” picture of diffusion via oxygen vacancies in α-Al2O3. However, consideration of the experimental activation energies in terms of the concentration of free point defects suggests that substantial modification of the classical picture may be necessary.

Journal ArticleDOI
TL;DR: Using the polarization selection rules for infrared spectroscopy, a silicon monohydride whose bond axis is parallel to the surface normal and two monohydrides whose bond axes are tilted with respect to the normal was observed at 2076, 2086, and 2095 cm−1.
Abstract: Multiple internal reflection (MIR) infrared spectroscopy has been used to study the adsorption of hydrogen on the Si(111)‐7×7 surface over the temperature range of 100–400 K. The high resolution of this technique has enabled us to observe three different silicon monohydride stretch modes at 2076, 2086, and 2095 cm−1. Using the polarization selection rules for infrared spectroscopy we have assigned these modes to a silicon monohydride whose bond axis is parallel to the surface normal and two monohydrides whose bond axes are tilted with respect to the surface normal. We have also observed the temperature dependent formation of surface dihydride and trihydride species. The formation of both the dihydride, observed at 2119 cm−1, and the trihydride, seen at 2143 cm−1, is favored by low adsorption temperatures. Finally, we also report a temperature dependent competitive formation between the two higher hydrides with the formation of the dihydride species maximizing near 200 K and lower temperatures favoring the...

Journal ArticleDOI
TL;DR: In this article, a saturation value of 1.4 monolayer bismuth enrichment was established on the grain boundaries in the 400-700°C temperature range at a rate which increased with temperature.

Journal ArticleDOI
01 Mar 1989-Langmuir
TL;DR: In this article, small-angle neutron-scattering structure factor measurements were made on sterically stabilized silica spheres dispersed in benzene up to volume fractions of 0.30.
Abstract: Small-angle neutron-scattering structure factor measurements were made on sterically stabilized silica spheres dispersed in benzene up to volume fractions of 0.30. Benzene is only a marginal solvent for the stabilizing layer on the surface of the particles. The particles are made attractive by lowering temperature. This attraction is modeled by a square well potential, the depth of which varies with temperature. At the highest temperature studied, our experimental system behaved effectively as an assembly of hard spheres, whereas at the lowest temperature the system approaches a spinodal. Using Baxter's theory we were able to evaluate the interaction parameters and to calculate the structure factor. Experimental structure factors were satisfactorily reproduced over the entire temperature range studied.

Proceedings ArticleDOI
03 Dec 1989
TL;DR: In this article, the reverse and nonideal forward currents in heavily doped diodes and in advanced bipolar transistors in the temperature range from 77 K to 300 K are presented.
Abstract: Measurements on the reverse and nonideal forward currents in heavily doped diodes and in advanced bipolar transistors in the temperature range from 77 K to 300 K are presented. A detailed comparison is made between these measurements and various models. It is shown that models from the literature fail to describe all observed phenomena. A model is proposed which is shown to provide a good description of the measured heavy-doping effects on recombination. The model describes the experimentally observed voltage and temperature dependence of both the nonideal forward and the reverse currents without the introduction of fitting parameters. It is shown that, for zero-bias depletion widths between 300 AA and about 700 AA, trap-assisted tunneling is important for reverse-biased junctions at room temperature. For zero-bias depletion widths less than 300 AA, the tunneling effects increase dramatically. Whereas trap-assisted tunneling has to be taken into account for the forward characteristic, the reverse characteristic is dominated by band-to-band tunneling. >

Journal ArticleDOI
TL;DR: In this article, the decay time of stretch-oriented poly(phenylenevinylene) (PPV) was studied in the temperature range 300∼12 K. The luminescence spectrum is composed of vibronic bands and a broad band, which are interpreted as caused by radiative annihilation of free and selftrapped excitons.
Abstract: Integrated luminescence spectra, time-resolved luminescence spectra, and luminescence decay times of stretch-oriented poly(phenylenevinylene) (PPV) are studied in the temperature range 300∼12 K. The reflectance spectrum at room temperature is also studied. The luminescence spectrum is composed of vibronic bands and a broad band, which are interpreted as caused by radiative annihilation of free and selftrapped excitons, respectively. Temperature dependence of the intensity of free-exciton luminescence and temperature dependence of the decay time are interpreted in terms of relaxation of excitons. The height of a potential barrier, which separates the free exciton state and the self-trapped state, is found to be 350 cm -1 . At 20 K, exciton relaxation toward the self-trapped state occurs by a quantum-mechanical tunneling process. The tunneling rate obtained is (90 ps) -1 .

Journal ArticleDOI
TL;DR: In this paper, the growth process of 2223 phase in a leaded Bi-Sr-Ca-Cu oxide system has been investigated under various oxygen partial pressures using differential thermal analysis, combined with XRD of the quenched specimen.
Abstract: The growth process of 2223 phase in a leaded Bi-Sr-Ca-Cu oxide system has been investigated under various oxygen partial pressures using differential thermal analysis, combined with XRD of the quenched specimen. It is shown that under a slow heating rate, the DTA curves exhibit two or three endothermic peaks between 820 to 900°C, and the peak positions are lowered with reduction in the O2 partial pressure. The 2223 phase is found to grow most efficiently in the partial melting state sandwiched between the two endothermic peaks, and the temperature range between the two peaks becomes maximum around 0.1-atm O2 partial pressure.

Journal ArticleDOI
TL;DR: In this paper, Ramaman spectroscopy has been used for the study of the oxidation of pure thin aluminum films in air and the films were annealed at 303, 423, 573, 673 and 773 K. The spectra were analysed in the range 230-900 cm −1 and the changes observed have been correlated with different stages of oxidation induced by heating.