Showing papers on "Temperature coefficient published in 1991"
01 Jan 1991
TL;DR: In this article, the authors measured the CO2/CO ratio formed by the heterogeneous reaction on the char surface for temperatures up to 1670 K and found an exponential decrease with a temperature coefficient of 3100/K.
Abstract: The ratio CO2/CO from oxidation of Spherocarb char has been measured over a wide temperature range making use of the electrodynamic balance where single particles are heated by laser irradiation but are immersed in room temperature gas. This has allowed measurement of the CO2/CO ratio formed by the heterogeneous reaction on the char surface for temperatures up to 1670 K. For these conditions, an exponential decrease with a temperature coefficient of 3100/K is found. The CO2/CO ratio is proportional to the oxygen partial pressure raised to a power of 0.21. These results are in substantial agreement with work reported at lower temperatures. At normal combustion temperature the CO2/CO ratio from heterogeneous reaction is less than 0.1. Gas phase oxidation of CO to CO2 near the char surface, however, can become important at high char temperatures, even in a gas maintained at room temperature, and can have an important impact on surface temperature. The temperature at which gas phase reactions begin to contribute to CO2 formation and surface temperature was found to be reduced by the presence of water vapor.
165 citations
TL;DR: In this article, the authors used dense ceramics with the chemical formula (1-X)Ba(Mg1/3Ta2/3)O3-XBaSnO3(X=0-0.15) for use as dielectric resonators.
Abstract: Dense ceramics with the chemical formula (1-X)Ba(Mg1/3Ta2/3)O3-XBaSnO3(X=0-0.15) are prepared for use as dielectric resonators. The obtained dielectric constant and Q value for Ba(Mg1/3Ta2/3)O3 were 24 and 43000 at 10 GHz, respectively. As X increased from 0 to 0.15, the temperature coefficient of resonant frequency decreased gradually from 5.4 to -0.5 ppm/ °C. At X=0.05, the Q value decreased drastically, and at X=0.10-0.15, the Q value increased to 33000 at 10 GHz. The specimens were investigated by scanning electron microscopy and X-ray diffraction analysis. It is found that Q improvement is not always dependent on the ordering structure of (1-X)Ba(Mg1/3Ta2/3)O3-XBaSnO3.
150 citations
TL;DR: In this article, electrical properties of BaTiO 3 and its solid solutions are reported at room and moderate temperatures in the range 300-500 K. The electrical properties are mainly analyzed in terms of the positive temperature coefficient of resistivity (the PTC effect).
77 citations
IBM1
TL;DR: In this paper, the Schottky-barrier heights of W and its silicide WSi2 on both n-type and p-type Si(100) have been measured in the temperature range 77-295 K with the use of currentvoltage and capacitance-voltage techniques.
Abstract: The Schottky-barrier heights of W and its silicide WSi2 on both n-type and p-type Si(100) have been measured in the temperature range 77–295 K with the use of current-voltage and capacitance-voltage techniques. Auger-electron and X-ray photoemission spectroscopies were used to characterize the Si(100) surfaces prior to metal deposition, and to monitor the reaction between W and Si. Silicide formation has very little or no effect on both the barrier height and its temperature dependence. The n-type barrier height for both the metal and the reacted silicide phase decreases with increasing temperature with a coefficient almost equal to the temperature coefficient of the indirect band gap in Si. The p-type barrier height does not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate from the predictions of models of Schottky-barrier formation based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect band gap. Along with results previously reported for metal(silicide)-Si systems with a wide range in metal electronegativity, the present results show that both the silicon barrier height and its temperature dependence are affected by the metal.
75 citations
TL;DR: In this paper, resistors with near zero temperature coefficient of resistance (TCR) were realized by optimizing the sputtering conditions, which demonstrated that the TCR was a strong function of substrate temperature during sputtering.
73 citations
TL;DR: In this paper, the free surface of a thin liquid layer gets tilted by a small angle proportional to the surface-tension temperature coefficient, and the effect is particularly large at the interface between two liquids with comparable densities.
Abstract: Under an applied horizontal temperature gradient, the free surface of a thin liquid layer gets tilted by a small angle proportional to the surface-tension temperature coefficient. The authors show the effect to be particularly large at the interface between two liquids with comparable densities. From the corresponding interfacial slope, measured optically under different boundary conditions, one could draw an accurate determination of the upper liquid free-surface coefficient.
69 citations
TL;DR: The change in refractive index with temperature (dn/dT) of four National Institute of Standards and Technology standard reference material (SRM) glasses have been measured over the range of 25° to 125°C as discussed by the authors.
Abstract: The thermooptic coefficients, i.e., the change in refractive index with temperature (dn/dT), of four National Institute of Standards and Technology standard reference material (SRM) glasses have been measured over the range of 25° to 125°C. The thermooptic coefficients of all four glasses, NBS-710 (a soda-lime silicate), SRM-711 (a lead silicate), SRM-717 (a borosilicate), and SRM-739 (silica) are positive and range in value from 2 × 10−6/K to 9.8 × 10−6/K. The differences in the dn/dT of these glasses arise from differences in the coefficient of thermal expansion and the temperature coefficient of the electronic polarizability.
58 citations
TL;DR: In this article, small-angle neutron scattering was used as a direct and accurate method to determine the temperature dependence of the unperturbed dimensions of a polyethylene polycarbonate.
Abstract: We demonstrate for the first time that small-angle neutron scattering can be used as a direct and accurate method to determine the temperature dependence of the unperturbed dimensions of a polymer. The sensitivity of the technique arises from the remarkable accuracy with which the random walk model can be used to describe the single-chain structure factor, and enables us to detect changes in the polymer radius of gyration of less than 0.5%. We present results for molten polyethylene and verify the accepted value of the temperature coefficient of thermal expansion.
48 citations
TL;DR: In this article, in situ HeNe laser ellipsometric measurements performed during and after rf plasma exposure of a Si wafer with or without oxide can be used to obtain the wafer temperature during plasma exposure.
Abstract: It is shown that in situ HeNe laser ellipsometric measurements performed during and after rf plasma exposure of a Si wafer with or without oxide can be used to obtain the wafer temperature during plasma exposure. The method utilizes either the temperature coefficient δn/δT of the refractive index of Si or the linear thermal expansion coefficient δl/lδT of SiO2. The values of these parameters have been redetermined in this work.
42 citations
Patent•
12 Mar 1991
TL;DR: In this paper, a positive temperature coefficient thermistor device includes an insulating casing housing a pair of thermistors arranged so that the rim thereof has at least a one-point contact with the tapered surfaces of the recesses.
Abstract: A positive temperature coefficient thermistor device includes an insulating casing housing a pair of positive temperature coefficient thermistors. Each of the inner surfaces of a pair of opposed walls consisting of the side walls and the top and bottom walls of the case is provided with a recess formed of at least one pair of tapered surfaces sloping from the walls provided with a pair of electrodes towards a common electrode located in the center. The thermistors are arranged so that the rim thereof has at least a one-point contact with the tapered surfaces of the recesses.
41 citations
TL;DR: In this article, the electrical properties of polyester elastomer filled with various metallic and ferrite fillers have been investigated as a function of temperature, frequency and filler concentration.
Abstract: The electrical properties, namely d.c. and a.c. conductivity, of polyester elastomer filled with various metallic and ferrite fillers have been investigated as a function of temperature, frequency and filler concentration. The temperature dependence of resistivity exhibited two regions of low and high activation energy (ΔE). The value of ΔE the lower temperature region (I) decreased while in the higher temperature region (II) it increased with the increase of work function of the metal used. Only in the case of ferrite-filled composites could a positive temperature coefficient of resistance be observed. The frequency dependence of conductivity revealed that there is a very large intergranular capacitance which was even more in the case of ferrite-filled samples than in metal-filled ones. The various results have been explained on the basis of Schottky barrier formation and the depletion regions formed near the polymer-metal interface.
TL;DR: In this paper, a systematic investigation on dielectric property changes with compositional variation was carried out for binary compound ceramics which were fabricated by the chemical powder preparation method in the identical systems Ln2O3-TiO2 (Ln=La, Nd and Sm).
Abstract: A systematic investigation on dielectric property changes with compositional variation was carried out for binary compound ceramics which were fabricated by the chemical powder preparation method in the identical systems Ln2O3-TiO2 (Ln=La, Nd and Sm). The temperature coefficient of permittivity (TCer) for those dielectrics was found to show a considerable deviation from a simple relation of TCer=-erαL. It also found that the solubility limits of Sm3+ into the Nd3+ lattice were greatly extended in the binary compounds up to ~80 or 90 mol%. Different dielectric property changes in the solid solutions with lanthanide substitution (La→Nd→Sm) were discussed on the basis of the different contributions of substituted ions to the polarization.
07 Oct 1991
TL;DR: In this paper, a novel compositionally graded heterostructure is used to grow high-quality thin-film one-sun and concentrator InP solar cells on GaAs substrates.
Abstract: High-efficiency, thin-film one-sun and concentrator InP solar cells grown on GaAs substrates are discussed. A novel, compositionally graded heterostructure is used to grow high-quality InP layers. One-sun cells have AM0 efficiencies as high as 13.7% at 25 degrees C (equivalent to 15.7% under the global spectrum). For the concentrator cells at 25 degrees C a peak conversion efficiency of 18.9% under 71.8 AM0 suns has been achieved. Under the direct spectrum, the equivalent efficiency is 21.0% at 88.1 suns. At 80 degrees C, the peak AM0 efficiency is 15.7% at 75.6 suns. Temperature coefficient data for the concentrator cells are also presented. Approaches for further improving the cell performance are discussed. >
TL;DR: In this paper, a model system of thick-film resistor (TFR) was prepared starting from RuO2 powders and a lead-free glass, and the electrical properties of the resistors were analyzed with particular attention to sheet resistance, temperature coefficient of resistance, size effects and piezoresistive properties.
Abstract: A model system of thick-film resistor (TFR) was prepared starting from RuO2 powders and a lead-free glass. The microstructural development was investigated by scanning and transmission electron microscopies, energy dispersive X-ray fluorescence, X-ray diffraction, thermogravimetry and other complementary techniques. The electrical properties of the resistors were analysed with particular attention to sheet resistance, temperature coefficient of resistance, size effects and piezoresistive properties. It was found that these simple systems are interesting with respect to their stability in ageing tests at relatively high temperatures but they are not promising for high-temperature piezoresistive gauges because of low strain sensitivity. Some samples were also prepared with a Bi2Ru2O7; a notable exchange reaction occurs between the conductive grains and the glass matrix which prevents the formation of pyrochlore-type based resistors with this glassy matrix.
TL;DR: In this paper, the impact of temperature and stress on the refractive index and optical components is discussed and the results indicate that the temperature coefficient of couplers and interferometers is of second order because of the dominance of the substrate elongation as the temperature changes.
Abstract: The presented concept of integrated optical sensors is based on silicon oxynitride thin films deposited on silicon. A thin-film technology compatible with silicon micromechanics and monolithic integration has been developed, including in particular PECVD and LPCVD techniques optimized for integrated optic purposes. Low-loss passive optical components have been realized and combined with fibre coupling, membrane fabrication and pin diode integration. After a brief survey on essential process steps, the impact of temperature and stress on the refractive index and the optical components is discussed. The results indicate that the temperature coefficient of couplers and interferometers is of second order because of the dominance of the substrate elongation as the temperature changes. In addition, the high temperature conductivity of the silicon substrate equalizes the temperature gradients. Two applications have been realized by this technology: a distance and a pressure sensor.
TL;DR: In this paper, up to 4 mol% Si was added using a new method as well as by the classical means as solid silica, which was found to result in a homogenization of the microstructure and an improvement in electrical properties.
Abstract: BaTiO3 positive temperature coefficient of resistance ceramics were prepared with the general composition (La0.002Ca
x
Ba0.998−x
) (Ti1.01−y
Mn
y
)O3 ·zSiO2 and sintered in air. The Ca content as well as the amount of doped Mn were varied ranging from 4–20 mol% and 0.02–0.04 mol%, respectively. Up to 4 mol% Si was added using a new method as well as by the classical means as solid silica. In the new method, the desired quantity of Si(OC2O5)4 (Si(OEt)4), contained in dry tetrahydrofurane (THF), was dropped under a slight stream of inert gas into the vigorously stirred aqueous slurry which was manufactured after the calcination process. The addition of Si by this technique was found to result in a homogenization of the microstructure and an improvement in electrical properties. The effect of Si on electrical properties is explained by the influence of the observed second phase on the equilibrium of Ba vacancies. The results of further variation of Ca and Mn contents are presented.
TL;DR: In this article, the intrinsic optical absorption has been measured for thin film samples made from bulk Hg1−xCdxTe with x ranging from 0165 to 045 and at temperature from 42 to 300 K.
TL;DR: In this article, measurements of the in-plane and c-axis resistivity in a superconducting Nd 1.85 Ce 0.15 CuO 4−δ single crystal are reported.
Abstract: Measurements of the in-plane and c -axis normal-state resistivity in a superconducting Nd 1.85 Ce 0.15 CuO 4−δ single crystal are reported. The resistivity anisotropy of this n-type material is ≤250, much smaller than BiSCCO and comparable to YBaCuO. Both, ϱ ab ( T ) and ϱ c ( T ) displays a metallic-like positive temperature coefficient of resistivity with a basic T 2 dependence. We discuss some possible origins of this peculiar temperature dependence.
Patent•
12 Aug 1991
TL;DR: In this article, a heating device for fixing a toner image on a sheet of image transferring medium, including a ceramic heat roller whose body is formed of a resistor material having positive temperature coefficient of resistance (PTC), capable of self-heating and self-regulating the temperature.
Abstract: A heating device, which can be used in the fixing unit of an image forming apparatus, such as an electrophotographic copying or printing machine, for fixing a toner image on a sheet of image transferring medium, includes a ceramic heat roller whose body is formed of a resistor material having positive temperature coefficient of resistance (PTC), capable of self-heating and self-regulating the temperature.
Patent•
23 Sep 1991
TL;DR: In this paper, a hair styling appliance having heat conductive portion for applying heat to the hair and an electrically energizable heater element located in thermal relationship with the heat conductively portion for causing it to be heated upon application of energy.
Abstract: The invention is directed to a hair styling appliance having heat conductive portion for applying heat to the hair and an electrically energizable heater element located in thermal relationship with the heat conductive portion for causing it to be heated upon application of energy. A temperature sensor is located in thermal relationship with the heat conductive portion. The temperature sensor is electrically connected to the heater element and has a positive temperature coefficient of resistance. A pulse switching device is operatively coupled to the heater and responsively coupled to the temperature sensor for controlling energization of the heater with temperature. A selectable temperature setting circuit is coupled to the pulse switching device for varying energization of the heater in accordance with a selected temperature operation. In a particular embodiment, the temperature sensor has a characteristic in the form of a curve with a rate of resistance which gradually changes over the desired temperature range resulting in stable temperature control and fast recovery from thermal loads.
TL;DR: In this article, a method is described for monitoring the moderator temperature coefficient of reactivity of pressurized water reactors based on the correlation of fluctuations in in-core neutron detector and core-exit thermocouple signals.
Abstract: In this paper a method is described for monitoring the moderator temperature coefficient of reactivity of pressurized water reactors based on the correlation of fluctuations in in-core neutron detector and core-exit thermocouple signals. The theoretical basis of the method is explained.
TL;DR: In this article, the dielectric properties and microstructures were investigated in ceramics of BaONd2O35TiO2 to which various amounts of Mn were added.
Abstract: The dielectric properties and microstructures were investigated in ceramics of BaONd2O35TiO2 to which various amounts of Mn were added. Although the behavior of the dielectric constant was independent of additional Mn, the temperature coefficient was improved considerably. The phases which were observed in these ceramics were characterized by means of electron probe microanalysis (EPMA) and X-ray diffraction method (XRD) in microareas. The shapes and areas of the phases varied with Mn content. The dielectric properties seemed to be mainly related to the properties of the matrix phase.
TL;DR: In this paper, the behavior of oxygen which is important to improve the PTCR jump has been examined by a tracer (18O) method and the depth profile of the tracer has been determined by means of Secondary ion mass spectrometry (SIMS).
Abstract: The characteristics of Positive Temperature Coefficient of Resistivity (PTCR) thermistors depend strongly on the atmosphere, especially oxygen, during the fabrication process. The PTCR jump decreases when the sample is heated in a reducing atmosphere, while it increases when the sample is heated in air. The behavior of oxygen which is important to improve the PTCR jump has been examined by a tracer (18O) method. The depth profile of the tracer has been determined by means of Secondary ion mass spectrometry (SIMS). The rate of penetration of oxygen into the grain boundary is very rapid and the PTCR jump depends on the amount of the oxygen penetrated into such a region.
TL;DR: In this article, a quantitative general effective media (GEM) equation is used to describe quantitatively the resistivity of an Fe3O4-epoxy composite system over a large range of volume fractions in terms of the resistivities of each component and two percolation morphology parameters.
Abstract: A quantitative general effective media (GEM) equation is used to describe quantitatively the resistivity of an Fe3O4-epoxy composite system over a large range of volume fractions in terms of the resistivities of each component and two percolation morphology parameters. One parameter is the critical (percolation) volume fraction, φc, and the other is an exponent,t. Preliminary models, also based on the GEM equation, are used to describe the positive temperature coefficient of resistivity (PTC) and the piezoresistivity (uniaxial pressure) of the composite when the composition is near the percolation threshold.
Patent•
27 Feb 1991
TL;DR: In this paper, a polycrystalline silicon resistor with an impurity in a high concentration and having a resistance adjusted by a current conduction therethrough at a current density of a threshold value or more is presented.
Abstract: A semiconductor device provided with a polycrystalline silicon resistor containing an impurity in a high concentration and having a resistance adjusted by a current conduction therethrough at a current density of a threshold value or more, which comprises: a polycrystalline silicon resistor containing a first impurity having a negative value of a temperature coefficient of resistance in a high impurity concentration region of said polycrystalline silicon resistor and a second impurity having a positive value of a temperature coefficient of resistance in a high impurity concentration region of the polycrystalline silicon resistor. A process for producing same is also disclosed.
TL;DR: In this paper, a new structure of a thin resistive film based on NiCr with a temperature coefficient of resistance close to zero is described, which is formed from two nitrogen-doped NiCr films with a sputtered aluminium film between them.
TL;DR: In this article, the authors examined the properties of actuators on several kinds of lead zinc niobate-based (PBZM) ceramics and found that the relative dielectric constant influences the electrostrictive constant, but hardly influences hysteresis, creep, nor the temperature coefficient near room temperature.
Abstract: The authors examined the properties of actuators on several kinds of lead zinc niobate-based (PBZM) ceramics. Bimorph type actuators were manufactured from four kinds of PBZM family ceramics, and these ceramics were investigated regarding the properties relevant to actuators, i.e., hysteresis, creep, temperature coefficient, and so on. As a result, it has been found for the PBZM family ceramics that the relative dielectric constant influences the electrostrictive constant, but hardly influences hysteresis, creep, nor the temperature coefficient near room temperature. Therefore, an ideal actuator which has small hysteresis, small creep, and a large electrostrictive constant can be obtained. The actuator which had the best property as an actuator in this examination had about 2%-hysteresis and creep, with a minus 1%-temperature coefficient near room temperature.
TL;DR: In this paper, the field-dependent tunnel-generation rate in GaAs has been experimentally determined from reverse-bias current measurements of MBE made submicron pin-structures.
Abstract: The field-dependent tunnel-generation rate in GaAs has been experimentally determined from reverse-bias current measurements of MBE made submicron pin-structures. The obtained results, tunneling rate and temperature coefficient, agree well with theoretical calculations.
Patent•
30 Aug 1991
TL;DR: In this paper, an electrothermal color-varying device inducing color change in a thermally color changing layer by heat generation in an electro-thermal heat-generating member, in which the heat generating member is composed of a non-metallic member hailing a positive temperature coefficient on the electric resistance at least in a temperature.
Abstract: There is disclosed an electrothermal color-varying device inducing color change in a thermally color-varying layer by heat generation in an electro-thermal heat-generating member, in which the heat-generating member is composed of a non-metallic member hailing a positive temperature coefficient on the electric resistance at least in a temperature; range 25°C to 65°C and a paticular volume resistivity, is adapted to generate heat by the application of a low voltage and is capable of self-control of the saturated heating temperature at an arbitrary temperature within a range of 25°C to 65°C, whereby improved safety is achieved without the danger of overheating or current leakage. Also there are disclosed toys utilizing such color-varying device.
TL;DR: In this article, the photoconductivity spectral response was measured for SnS single crystals at different temperatures with polarized light with the plane of polarization parallel to the a- and b-crystallographic axes which lie in the cleavage.
Abstract: The photoconductivity spectral response was measured for SnS single crystals at different temperatures with polarized light with the plane of polarization parallel to the a- and b-crystallographic axes which lie in the plane of cleavage The photoconductivity energy gap was determined from the spectral response by the Moss rule The room temperature photoconductivity energy gap was found to be (161 ± 0031) eV and (1139 ± 0015) eV for the a- and b-axes, respectively The temperature dependence of the photoconductivity energy gap was found to be linear between 91 and 300 K with a negative temperature coefficient equal to -(037 ± 001) meV/K for the b-axis The results for the a-axis showed large discrepancy which was attributed to crystal lattice bending which was introduced during the cleavage process The minority carriers lifetime was determined from the photoconductivity frequency response which was found to be characterized by two different lifetimes