Showing papers on "Atmospheric temperature range published in 1973"

Optical and photoelectric properties and colour centres in thin films of tungsten oxide

Abstract: Thin films of Wo3 deposited on quartz substrates at room temperature have been shown to be amorphous in structure. The optical absorption spectra of the amorphous and crystalline films have been measured in the temperature range 110° to 500°K. The fundamental absorption edge of an amorphous film occurs at 3800 A which on crystallization moves to 4500 A. On the high-energy side of the absorption edge several absorption peaks are resolvable in both types of film. The frequency dependence of the absorption coefficient below 104 cm−1 is described by an expression of the form K (v, T) = K 0 exp[− (β/kT) (E 0 − hv)] and above 104 cm−1 it follows a square law dependency. The temperature coefficient of the band edges was found to be − 5.0 × 10−4 eV/°K and the estimated band gaps at 0°K were found to be 3.65 and 3.27 eV for the amorphous and crystalline films, respectively. The electrical conductivity of a thin film has been measured in the temperature range 298–573°K and the activation energy was found t...

Study of Semiconductor-to-Metal Transition in Mn-Doped Fe Si 2

Abstract: The electrical resistivity, the thermoelectric power, and the Hall coefficient for Fe${\mathrm{Si}}_{2}$ doped with Mn or Co have been measured over the temperature range 300-1400 K. The energy gaps deduced from the slopes of curves of the resistivity versus reciprocal absolute temperature decrease with increasing Mn concentration. The resistivities and thermoelectric powers show a semiconductor-to-metal transition with hysteresis, and the transition temperature decreases with increasing Mn concentration. Specimens both doped with Mn and undoped are found to be $p$-type semiconductors in the temperature range below the transition temperature. The added Mn acts as an acceptor. The analysis of resistivity in the semiconducting state was based on a model predicting that the narrow band in the metallic state is split by the crystalline-structure distortion. The density of states for the undoped specimen is found to be 7.46\ifmmode\times\else\texttimes\fi{}${10}^{22}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Assuming that the value of the density of states is invariable in all specimens, the analyzed results are in reasonable agreement with the resistivities observed in the intrinsic region.

Recombination mechanisms in 8–14‐μ HgCdTe

Abstract: Photoconductive measurements on n‐type Hg1−xCdxTe, for compositions of 0.195 < x < 0.210, have been carried out in the temperature range 65–300°K. A comparison of the experimental data with simple band‐to‐band recombination theory indicates that the lifetime in the intrinsic range of temperatures is determined by an Auger limited process. The measured variation of lifetime with temperature can be used to predict values for the Auger limited lifetime in intrinsic material, τAi, over the entire temperature range 65–300°K. Calculations, using these values of τAi, for the extrinsic temperature range (<100°K) indicate that for our purer material (ND−NA≳4×1014 cm−3;μ77≳1.5×105 cm2 V−1 sec−1), the lifetime is still determined by an Auger limited band‐to‐band process. In somewhat more compensated material (ND−NA<4×1014 cm−3;μ77≲1.5×105 cm2 V−1 sec−1), Shockley‐Read limited lifetimes are observed, although in the majority of samples measured the electron lifetime is independent of temperature. However, in some ext...

Self‐diffusion and viscosity of some liquids as a function of temperature

Abstract: Self-diffusion coefficients of 15 liquids have been measured as a function of temperature between their melting and boiling points. The systems investigated were the benzenes, C6H5X where X = H, F, Cl, Br, and I, n-paraffins, CnHn + 2 where n = 7, 9, 10, 12, 14, 16, and 18, acetone, acetic acid and water. The pulsed nmr technique was employed for the diffusion measurements. In addition, the viscosities of the halogenated benzenes have been measured between 20°C and their melting points. The diffusion results obtained in this study have been found in excellent agreement with the best values available for benzene (Collings and Mills, 1970) and water (Longworth, 1960). The relation between the apparent molecular diameter d (d = 2.24(η VD/RT)1/2) and the critical volume as suggested by Dullien (1972) has been extended to include the temperature dependence of d. It is also shown that the temperature dependence of d is similar for all liquids studied here with respect to the reduced temperature. The increase of d for Tr < 0.46 shows the invalidity of the Stokes-Einstein relation for this temperature range (Tr = T/Tc). A normalized plot of d has been found very useful in checking the consistency of viscosity and self-diffusion data. The relations proposed in this work can be used to predict self-diffusion coefficients and viscosities over the normal liquid range.

Formation kinetics and structure of Pd2Si films on Si

Abstract: Backscattering and X-ray techniques have been used to study properties of palladium silicide (Pd2Si) formed by evaporating thin Pd layers on Si followed by heat treatment. The rate of formation of Pd2Si in the temperature range of 200–275°C has been measured by 2-MeV 4He+ ion backscattering. The Pd2Si layer is found to grow at a rate proportional to the square root of time for thicknesses ranging from approximately 200–4000 A. The rate of growth is found to be independent of Si substrate orientation or doping type and the rate constant is found to fit a single activation energy of Ea = 1·5±0·1 eV over the temperature range measured. X-ray diffraction indicates the structure to be Pd2Si with the basal plane roughly parallel to the substrate surface for films formed on 〈111〉, 〈110〉, 〈100〉 and evaporated (amorphous) silicon substrates. The degree of preferred orientation is markedly stronger on [111] Si. Ion channeling measurements confirm that in this case the c-direction of the Pd2Si is parallel with the [111] direction in the underlying Si.

Temperature dependent Raman study of molecular motions and interactions of CH3 I in the liquid phase

Abstract: The polarized and depolarized components of the 524 cm−1 Raman band in liquid methyl iodide were measured between 196 and 300°K. A technique, utilizing the isotropic scattering intensity, allowed the separation of reorientational line broadening of the anisotropic spectrum from the broadening due to other processes. The reorientational correlation times derived from the anisotropic Raman spectrum were found to agree well with those obtained by other techniques throughout the temperature range studied. The temperature dependence of the isotropic correlation times was opposite to that predicted by current theories of vibrational relaxation and collisional broadening. The depolarization ratio was also measured as a function of temperature and is seen to vary quite markedly. The depolarized low frequency spectra of methyl iodide were also studied and the results were fit to a theoretical expression for collision induced scattering to obtain values for the linewidth parameter Δ. The temperature dependence of Δ...

The Effect of Temperature and Pressure on the Refractive Index of Some Oxide Glasses.

Abstract: The change in refractive index with temperature has been determined for some oxide glasses from about -200 to 700 °C. The change in refractive index with applied hydrostatic pressure has been determined at room temperature from a pressure of 105 to 108 Pa. All measurements were made using the yellow spectral line of helium. A calcium aluminate glass, an aluminum magnesium phosphate glass, a binary barium borate glass and a multicomponent germanate glass were studied, as were four commercial specimens of fused silica. From the data at room temperature, it has been possible to calculate the change in electronic polarizability with temperature at constant volume. This parameter has been found to be very high for the glasses as compared to crystals, and this agrees with the results of earlier research on silica-based optical glasses. Furthermore, over the entire temperature range, the change of refractive index with temperature is shown to be due predominantly to the temperature dependence at constant volume of the electronic polarizability. The relevance of the data to the molecular scattering of light in glasses is discussed.

Thermodynamic properties of hydrogen and deuterium dissolved in palladium at low concentrations over a wide temperature range

Abstract: The equilibrium pressures of the Pd/H2 and Pd/D2 systems have been measured in the temperature range from –100°C to 350°C for values of H(D)-to-Pd, atomic ratio, in the approximate range from 0.0005 to 0.005. These data were obtained in an ultra-high vacuum apparatus with large samples of low surface area. Partial thermodynamic data have been obtained from these equilibrium data; a significant temperature dependence is reported for the relative partial molar enthalpies and entropies.

Hopping conductivity in highly anisotropic systems

Abstract: The temperature dependence of the phonon-activated d.c. conductivity is calculated for quasi one- and two-dimensional systems. For a one-dimensional system it is shown that the behaviour of σ(T) depends on the length of the chains and one obtains 1n σ = 1n σ0 − (T 0/T)I/n where n is 1 or 2, depending on temperature range and geometry. For low temperatures, purely one-dimensional hopping does not exist and an anisotropic two-dimensional model must be used.

The thermal conductivity of NiO and CoO at the Neel temperature

Abstract: The thermal conductivity of singly crystals of NiO has been measured in the temperature range 100-650K and that of CoO in the range 100-450K, both ranges including the Neel temperature. Sharp minima at the magnetic transition are qualitatively explained in terms of Stern's theory of the critical scattering of phonons by the spin system. Data are also reported on the specific heat and electrical resistivity of the crystals around the magnetic transition, the former showing critical behaviour which is very similar to that found in many other ordered systems. There is evidence from the latter of a divergence in the rate of change of resistivity with temperature, behaviour so far reported only in magnetic metals.

The elastic constants and thermal expansion of single-crystal CdTe

Abstract: The elastic constants and thermal expansion of single-crystal CdTe have been measured in the temperature range 42-300 K. The values of elastic constants obtained at 298 K were C11=538×1010 N m−2, C12=374×1010 N m−2 and C44=2018×1010 N m−2. Their temperature variation is in good agreement with Vekilov and Rusakov's (1971) values and the temperature dependence of the thermal expansion is similar to the other measurements in the literature. An anomaly in both parameters is observed, which has hitherto not been reported, and is tentatively attributed to a change in ionicity. The Debye temperature at 0 K is calculated from the elastic constants and a value of 1627 K obtained.

Pressure-volume-temperature properties of amorphous polymers: empirical and theoretical predictions

Abstract: Equation of state data on several amorphous polymers, viz., polystyrene, poly(methyl methacrylate) and poly(vinyl chloride) are considered from two points of view. First in terms of the empiricalTait equation applied to the liquid as well as the glassy state with a single disposable and temperature dependent parameter. These results supersede and extend an earlier analysis. Good agreement between independent investigators is obtained for polystyrene. Secondly, the hole theory ofSimha- Somcynsky is applied to the liquid state of these polymers. The isobar at atmospheric pressure and the compressibility factorpV/T up to pressures of about 2 kbar are analyzed in detail and the numerical values of the characteristic volume (V*), temperature (T*), and pressure (p*) parameters are established. The evaluation of the theoretical expressions requires the numerical solution of a transcendental equation for the hole fraction as a function of the reduced volume and temperature, which arises from the extremum condition on the partition function. At atmospheric pressure, this computation is avoided and the evaluation facilitated by means of a simple and accurate interpolation formula for the theoretical volume-temperature relation. In this manner,V* andT* are readily obtained. A series of theoretical reduced isochores are presented in graphical form, which encompass a change in density of 15% and a temperature range of at least 200 degrees. A single pressure datum then provides an estimate ofp* and thus of the complete equation of state. Finally we note that the reducedTait parameterB, as computed from the theory, exhibits the exponential variation with temperature, observed experimentally.

Influence of particle sizes and environmental conditions on high temperature pyrolysis of cellulosic material. I. Theoretical

Abstract: A mathematical model based on unreacted-core shrinking model is developed to describe the pyrolysis phenomena of the cellulosic materials in the temperature range of 700–1470 °K. The relative importance of each model parameter is studied by applying the sensitivity analysis. The heat transfer control region and kinetic reaction control region are obtained from the developed model. The shift of controlling mechanism is dependent on the particle size and the wall temperature. The effect of heat of reaction on the temperature of the particle is also discussed.

Thermodynamic Quantities of Alkali Silicates in the Temperature Range from 25°C to Melting Point

Abstract: The heat contents of the alkali silicate glasses and crystals have been measured from 25°C to melting temperature with a continuous high-temperature calorimeter.The entropy in the above temperature range is determined for the glasses and crystals of the composition R2O⋅2SiO2 (R=Li, Na, K). The free-energy change is calculated for the reaction of forming the glasses from the crystals. The free-energy values thus obtained are compared with those calculated from two approximate equations, ΔG=ΔT⋅ΔHf/Tm and ΔG=(ΔT⋅ΔHf/Tm)⋅(T/Tm). This comparison indicates that the free-energy values from these equations are inapplicable to the discussion on the kinetic process except for the case in the narrow temperature range near the melting point.The relation between the heat capacity per mole of SiO2 and composition expressed by the mole ratio R2O/SiO2 at 300° and 600°C is also investigated. In the system Na2O-SiO2 crystals, the heat capacity increases linearly with Na2O/SiO2 ratio. The slope of this straight line and the intersection at zero Na2O composition approximately correspond to the heat capacity of crystalline Na2O and that of crystalline SiO2, respectively. From this result, it can be assumed that the additivity approximately holds for the heat capacity of Na2O-SiO2 crystals.For Na2O-SiO2 and K2O-SiO2 glasses and supercooled liquids, the composition dependence of heat capacity shows an inflection at the composition of R2O/SiO2=0.5. These results are discussed from the view point of structure of glass and liquid.

Vibrational relaxation of HF in the temperature range 600–2400 °K

Abstract: Hydrogen fluoride vibrational deactivation by HF, Ar, and F atoms has been studied in the temperature range 600–2400 °K using the shock tube‐laser‐induced fluorescence method Mixtures of HF–Ar and F2–HF–Ar were heated by reflected shock waves; following establishment of thermal equilibrium, HF was vibrationally excited by pulsed radiation from an HF pin laser Relaxation times were obtained from the time‐resolved decay of the laser‐induced vibrational fluorescence Measurements of relaxation by F atoms were limited to temperatures > 1500 °K, where F2 dissociates completely behind the reflected shock wave The HF self‐relaxation time, p τHF–HF, exhibits a broad maximum with temperature, peaking at ≈ 010 μsec · atm near 1400 °K Fluorine atoms were found to be 2–5 times more efficient than HF molecules for HF vibrational deactivation over the range 1500–2400 °K Argon is a very inefficient collision partner; values of p τHF–Ar over the range 800–2400 °K are reported This is the first study in which the maximum of pτHF–HF with temperature has been fully described; the present results both confirm and unify those of previous high (> 1400 °K) and low (< 1000 °K) temperature studies

Thermodynamic Lattice and Electronic Properties of Small Particles

Abstract: Specific-heat measurements were performed on small lead particles (22, 37, and 60 \AA{}) and 22 \AA{} indium particles over the temperature range 1.5-15 K. For all sizes the enhancement of the specific heat due to the increased importance of low-frequency surface modes and attendant depletion of higher-frequency modes was observed. Although the magnitude of the observed surface-phonon specific heat agrees reasonably well with theoretical estimates at intermediate temperatures, the observed enhancements apparently are not proportional to the surface area and do not exhibit quadratic temperature dependence. The rapid decreases of the heat capacity at lowest temperature appear to be consistent with the estimates of low-frequency cutoffs in the phonon spectrum caused by quantum size effect. At temperatures around one-tenth of the bulk Debye temperature the surface specific heats exhibit maxima. Differences in the electronic specific heat in the superconducting state between small particles and the bulk were observed. The transition-temperature behavior of lead and indium particles is also discussed.

Densification of alkali silicate glasses at high pressure

Abstract: The densification behavior of a number of alkali silicate glasses has been investigated using a Bridgman anvil high pressure device. The pressure range of the investigation was 10 to 60 kilobars; the temperature range was 100 to 400°C. In all cases, the densification was found to increase with increasing temperature and pressure. In the two systems where compositional variations were explored, Na2OSiO2 and K2OSiO2, a pronounced maximum in densification in the vicinity of 10 mole % alkali oxide was observed (for a given temperature and pressure). These maxima are taken to reflect a competition between two processes, one of which — the variation of molecular mobility with composition — should lead to increasing densification with increasing alkali concentration. Several possibilities are discussed for the decrease in densification with alkali oxide concentrations greater than about 10% (to values smaller than that of SiO2 in some cases). The present results are related to those obtained in previous investigations of the densification of oxide and polymeric glasses.

On optical polarization measurements in liquid crystals

Abstract: ``Compensated'' nematic mixtures of cholestryl derivatives are very well suited as anisotropic solvents for optical polarization studies in the ultraviolet since these compounds are transparent to about 240 nm and can be homogeneously oriented by dc electric fields. Such mixtures have been prepared in a temperature range between 20 and 100 °C by only slight changes in the composition. Polarization experiments have been performed both in the liquid state above room temperature and in the ordered frozen state below −30 °C. The degree of absorption polarization has been calculated as function of the elements exi of the molar extinction coefficient tensor and the average orientations (order parameters Sxi xi) of the solute molecular axes xi. For symmetric molecules all elements exi (λ) and order parameters can be determined. Results of our polarization studies of anthracene, chrysene and a charge transfer complex are presented. Moreover, it is shown that measurements of the circular dichroism, observed in the...

Ionic thermal current study of the α′ process in poly(hexamethylene adipamide)

Abstract: The ionic thermoconductivity (ITC) method has been used to study the α′ transition in the polyamide (nylon 66). Depending on the thermal history of the sample, the maximum of the thermocurrent peak attributed to the α′ relaxation is found somewhere between ca. 45°C and ca. 66°C; on one heating, it shifts to higher temperatures. The high sensitivity and resolving power of the ITC method permit resolution of this peak into four elementary “pure” activated processes, with constant activation energies in the relevant temperature range. Each of the four corresponding relaxation times follows an Arrhenius law, with a well-defined characteristic temperature T0 = 83°C at which all these relaxation times are equal. When this last result is interpreted in the light of Eyring's or Bauer's theory, it gives a linear relation between “apparent” activation entropy and activation enthalpy of the elementary processes. The characteristic temperature T0 is independent of the thermal history of the sample, and the temperature shift of the thermocurrent maximum can be interpreted by the observed variation of the relative intensities of the elementary processes, without modification of their other characteristic features.

Epitaxial growth of silicon from SiH4 in the temperature range 800–1150°C

Abstract: Results on the deposition of silicon from SiH 4 are reported for a temperature range 800–1150°C. Deposition was carried out at atmospheric pressure and at reduced pressures in the range 0·2-1 Torr where it was possible to maintain an h.f. glow discharge in the reactor tube. Using the h.f. discharge good quality epitaxial growth was achieved at 800°C for both undoped and heavily doped n -type layers. The main advantage of using the discharge is thought to be the marked cleanup it gives to the substrate prior to deposition taking place.