Electrical conduction in granular Cu–SiO2 films

1982 ◽  
Vol 60 (10) ◽  
pp. 1484-1489 ◽  
Author(s):  
N. Savvides ◽  
S. P. McAlister ◽  
C. M. Hurd
Keyword(s):  
Electrical Resistivity ◽  
High Temperature ◽  
Low Temperature ◽  
Local Minimum ◽  
Temperature Dependent ◽  
Complex Behaviour ◽  
Intermediate Regime ◽  
Sputtered Films ◽  
Metal Volume ◽  
Localization Of Electrons

We have measured the temperature dependence of the electrical resistivity ρ of Cu – SiO2 co-sputtered films in the range 4–300 K for metal volume fractions between 0.5 – 0.8. The films range between the metallic (ρ ~ T) and "strongly-localized" (log ρ ~ T−1/2) regimes. In the intermediate regime we find a complex behaviour for ρ(T) with a concentration dependent local minimum that separates the low temperature ρ ~ log T and the high temperature ρ ~ T behaviour. We attribute this to temperature dependent localization of electrons.

An investigation into the effect of temperature-dependent stiffness of rail pads on vehicle-track coupled vibrations

2016 ◽  
Vol 231 (4) ◽  
pp. 444-454 ◽  
Author(s):  
Kai Wei ◽  
Zi-xuan Liu ◽  
Ying-chun Liang ◽  
Ping Wang
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Thermoplastic Polyurethane ◽  
Testing Machine ◽  
Center Frequency ◽  
Effect Of Temperature ◽  
Static Stiffness ◽  
High Temperature Stability ◽  
Temperature Dependent ◽  
Coupled Vibrations

To consider the rail pads of thermoplastic polyurethane elastomer (TPE), chloroprene rubber (CR), and ethylene propylene diene monomer (EPDM) that are usually used in the Chinese subway as test subjects, their static stiffness at temperatures of −40℃ to 70℃ was measured by a universal testing machine equipped with a temperature control box. Then, the influence of the temperature-dependent stiffness of the rail pads on the vertical vehicle-track coupled vibrations was investigated with application of a vehicle-track coupled dynamic model. It was found that the static stiffness of these rail pads exhibits a nonlinear variation with temperature. Their static stiffness is considerably sensitive to temperatures below 20℃, when the CR rail pad is the most sensitive. At temperatures above 20℃, their static stiffness slightly alters with increasing temperature. The temperature-dependent stiffness of these rail pads mainly affects the vertical vibrations of the vehicle system above the one-third octave center frequency of 31.5 Hz and the vertical rail vibrations near the center frequency of 63 Hz. Moreover, the influence of the low-temperature stiffness of rail pads at −40℃ to 20℃ is far greater than the effect of the high-temperature stiffness of rail pads at 20–70℃. Thus, TPE, CR, and EPDM rail pads have excellent high-temperature stability and adverse low-temperature sensibility.

scholarly journals Switchable Metasurface with VO2 Thin Film at Visible Light by Changing Temperature

Photonics ◽  
2021 ◽  
Vol 8 (2) ◽  
pp. 57 ◽  
Author(s):  
Jin-Kyu Yang ◽  
Hyeon-Seok Jeong
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Optical Sensors ◽  
Beam Steering ◽  
Incident Light ◽  
Visible Region ◽  
Polarization Conversion ◽  
Temperature Dependent ◽  
Beamforming Antennas ◽  
Change Material

We numerically demonstrated switchable metasurfaces using a phase change material, VO2 by temperature change. The Pancharatnam–Berry metasurface was realized by using an array of Au nanorods on top of a thin VO2 film above an Au film, where the optical property of the VO2 film is switched from the insulator phase at low temperature to the metal phase at high temperature. At the optimal structure, polarization conversion efficiency of the normal incident light is about 75% at low temperature while that is less than 0.5% at high temperature in the visible region (λ∼ 700 nm). Various functionalities of switchable metasurfaces were demonstrated such as polarization conversion, beam steering, Fourier hologram, and Fresnel hologram. The thin-VO2-film-based switchable metasurface can be a good candidate for various switchable metasurface devices, for example, temperature dependent optical sensors, beamforming antennas, and display.

scholarly journals Investigation of the Polymorphism of Osmium Tetrachloride

1969 ◽  
Vol 24 (2) ◽  
pp. 200-205 ◽  
Author(s):  
Paul Machmer
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Temperature Dependent ◽  
Orthorhombic Unit Cell ◽  
Magnetic Susceptibilities ◽  
X Ray ◽  
Space Groups ◽  
Temperature Form ◽  
High Temperature Form ◽  
First Ionization Potential

Depending on the method of preparation, osmium tetrachloride may be obtained in two different crystalline modifications, namely the high-temperature and the low-temperature forms. Both these species have been identified by elemental analysis and characterised by their respective x-ray powder photographs and magnetic susceptibilities. The x-ray powder data of the high-temperature form are tentatively rationalized in terms of an orthorhombic unit cell with the following dimensions: a = 12.08 A, b = 11.96 Å and c = 11.68 A. From the x-ray powder digram of the lowtemperature form the cubic lattice constant a = 9.95 Å is deduced. Reflection conditions for hkl and h00 are indicative of the space groups 06(P4332) and 07(P4132). Both compounds are paramagnetic and display low magnetic susceptibilities as a consequence of strong spin-orbit coupling. The high-temperature form exhibits the temperature-independent magnetic susceptibility χmole = +1080 × 10-6 c.g.s. units, whereas for the low-temperature form the value is χmole = +880 × 10-6 c.g.s. units (at 300°K). The latter susceptibility is temperature dependent. Some regularities between the uptake of chlorine by second- and third-row transition metals and the first ionization potential of the metals involved are discussed.

Weak Localization Effects in Fluorineintercalated Graphite Fibers

1990 ◽  
Vol 209 ◽  
Author(s):  
S.L. Di Vittorio ◽  
M.S. Dresselhaus ◽  
V. Bayot ◽  
L. Piraux ◽  
J-P. Issi ◽  
...  
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Low Temperatures ◽  
Weak Localization ◽  
Temperature Dependent ◽  
Weak Magnetic Fields ◽  
Graphite Fibers ◽  
Temperature Dependent Resistivity ◽  
High Fields ◽  
Hole Interaction

ABSTRACTThe intercalation of fluorine into graphite introduces defects into the highly crystalline pristine fibers. These defectsare studied using temperature-dependent resistivity and magnetoresistance measurements. A logarithmic increase in resistivity at low temperature is observed, whereas the high temperature behavior is metallic. At weak magnetic fields and low temperatures, a negative magnetoresistance is observed, which becomes positive at high fields. These effects are explainedusing the two theories of weak localization and hole-hole interaction. In the light of TEM pictures of the microstructure of the fluorinated fibers, the origin of the defects in the intercalated fibers is discussed.

Formation and Conductive Properties of Miniaturized Fullerite Sensors

2001 ◽  
Vol 705 ◽  
Author(s):  
Alexander S. Berdinsky ◽  
Dietmar Fink ◽  
Alexander V. Petrov ◽  
Manfred Müller ◽  
Lewis T. Chadderton ◽  
...  
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Low Temperature ◽  
Negative Temperature ◽  
Heavy Ion ◽  
Complex Behaviour ◽  
Ion Tracks ◽  
Temperature Coefficients ◽  
Swift Heavy Ion ◽  
Conductive Properties

AbstractFullerite nanotubules of 100 nm to 2 μm radius, up to 200 nm wal thickness and 10 μm length were produced inside etched swift heavy ion tracks in a polymer, by letting fullerence precipitate from a concentrated C60 solution within the tracks. After contacting the tubules on both sides with silver paste, their resistivity was measured as a function of temperature. All of the 13 prepared samples show a complex behaviour that can be described by tw Arrhenius curves, the low temperature branch with activation energy Eact = (1.77 ± 0.2) eV stemming from pure C60, and the high temperature branch being tentatively ascribed to C60Agx with x ≍ 12.4 and Eact = (0.68 ± 0.2) eV, as the letter compound has found to be produced at ambient temperature by C60 / Ag thermal intermixture. Such samples with tw branches of negative temperature coefficients of resistance might be useful to construct advanced thermoresistors.

scholarly journals Hydrogen-bonding in mono-, di- and tetramethylammonium dihydrogenphosphites

2021 ◽  
Vol 236 (1-2) ◽  
pp. 33-41
Author(s):  
Matthias Kogler ◽  
Berthold Stöger
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
High Temperature ◽  
Low Temperature ◽  
Crystal Structures ◽  
Point Symmetry ◽  
Temperature Dependent ◽  
Threefold Axis ◽  
Quotient Graphs ◽  
Hydrogen Bonding Networks

Abstract The crystal structures of methylammonium and dimethylammonium dihydrogenphosphite (MA⋅H2PO3, I2/a and DMA⋅H2PO3, P 2 1 / c $P{2}_{1}/c$ ) are built of infinite chains of hydrogen bonded H 2 P O 3 − ${\mathrm{H}}_{\mathrm{2}}\mathrm{P}{\mathrm{O}}_{\mathrm{3}}^{-}$ anions. The chains are connected by the ammonium cations via hydrogen bonding to di- (DMA⋅H2PO3) and triperiodic (MA⋅H2PO3) networks. Tetramethylammonium dihydrogenphosphite monohydrate (TMA⋅H2PO3⋅H2O) features temperature dependent dimorphism. The crystal structure of the high-temperature (HT, cubic P213) and low-temperature (LT, orthorhombic P212121) phases were determined at 150 and 100 K, respectively. The hydrogen bonding network in the HT phase is disordered, with H 2 P O 3 − ${\mathrm{H}}_{\mathrm{2}}\mathrm{P}{\mathrm{O}}_{\mathrm{3}}^{-}$ and H2O being located on a threefold axis and is ordered in the LT phase. On cooling, the point symmetry is reduced by an index of 3. The lost symmetry is retained as twin operations, leading to threefold twinning by pseudo-merohedry. The hydrogen-bonding networks of the HT and LT phases can be represented by undirected and directed quotient graphs, respectively.

Semiconducting Molybdenum Pyrochlores for high Temperature Applications

1998 ◽  
Vol 512 ◽  
Author(s):  
V. Ponnambalam ◽  
U. V. Varadaraju
Keyword(s):  
Activation Energy ◽  
Electrical Resistivity ◽  
High Temperature ◽  
Low Temperature ◽  
Solid Solutions ◽  
Power Factor ◽  
Charge Carriers ◽  
Temperature Range ◽  
Maximum Power Factor ◽  
Increasing Temperature

ABSTRACTThe solid solutions (Y1-xYbx)2Mo2O7 were prepared and the systematic changes in the electrical resistivity (ρ=l/σ), thermopower (S) and power factor (S2σ) have been studied in the temperature range 300–900 K. The lattice parameters ‘a’ and ‘c’ are smaller for higher Yb3+ content phases due to smaller Yb3+ radius and a small tetragonality is observed for all the phases. Semiconducting behaviour is seen for all compositions with systematic increase in activation energy with increasing Yb content. All compositions show negative thermopower indicating electrons are the majority charge carriers in the temperature range of measurements. The calculated power factor values S2σ increase with increasing temperature in the low temperature region and a maximum power factor of ∼0.76×10−7 Wcm−1K−2 is observed at 650K.

scholarly journals Temperature-induced Glucosinolate Accumulation Is Associated with Expression of BrMYB Transcription Factors

HortScience ◽  
2013 ◽  
Vol 48 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Veronica L. Justen ◽  
Vincent A. Fritz
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Gene Expression Analysis ◽  
Tissue Type ◽  
Temperature Dependent ◽  
Temperature Regimes ◽  
Health Promoting ◽  
Transcription Factor Expression ◽  
Low Temperature Treatments

Turnips (Brassica rapa. subsp. rapa L.) produce glucosinolates (GSLs), thioglucosides whose hydrolyzed derivatives have been shown to provide chemopreventive benefits. Two cultivars of turnips [‘Just Right’ (JR) and ‘Scarlet Queen’ (SQ)] were grown under three different temperature regimes to assess the role of temperature on GSL production in roots and shoots. When compared with low-temperature treatments, high-temperature treatments increased total and individual GSLs in a tissue- and genotype-specific manner. When compared with low-temperature treatments, total GSLs were ≈70% and 130% higher in JR shoots and roots, respectively, grown at high-temperature treatments. High temperatures also increased total GSLs in SQ shoots and roots by ≈80% and 85%, respectively, when compared with low temperatures. Gluconasturtiin (GNS, 2-phenylethyl GSL) concentration was inversely correlated with temperature with high-temperature treatments resulting in 20% and 48% less GNS than low-temperature treatments in JR and SQ roots, respectively. The indolic GSL, 1-methoxyglucobrassicin (1MGB; 1-methoxy-3-ylmethyl GSL), was the root GSL most elevated by increased temperature resulting in a 1000% increase on average in both cultivars between the low- and high-temperature treatments. These results show promise for the use of temperature to enhance the health-promoting properties of turnip because 1MGB has potent chemopreventive effects. Gene expression analysis suggests that some BrMYB transcription factor expression levels are associated with temperature-dependent changes in GSL accumulation; however, this association varies between cultivar and tissue type.

Monoclinic-to-orthorhombic phase transition of the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal with temperature-dependent dynamic molecular disorder

2016 ◽  
Vol 72 (12) ◽  
pp. 971-980 ◽  
Author(s):  
Tze Shyang Chia ◽  
Ching Kheng Quah
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Structural Phase ◽  
Point Group ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Temperature Dependent ◽  
Space Group ◽  
Low Temperature Phase

As a function of temperature, the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal, C6H12N4·2C8H8O2, undergoes a reversible structural phase transition. The orthorhombic high-temperature phase in the space groupPccnhas been studied in the temperature range between 165 and 300 K. At 164 K, at2phase transition to the monoclinic subgroupP21/cspace group occurs; the resulting twinned low-temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/0-10/00-1. Systematic absence violations represent a sensitive criterium for the decision about the correct space-group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low-temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point groupmmmand the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to at2structural phase transition. The asymmetric unit of the low-temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2-methylbenzoic acid; it is smaller by a factor of 2 in the high-temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three-molecule aggregate; the low-temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high-temperature phase. In both phases, one of these three-molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 Kvia0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature-dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.

Transport Properties of the Ferromagnetic Metals. I. Cobalt

1973 ◽  
Vol 51 (12) ◽  
pp. 1247-1256 ◽  
Author(s):  
M. J. Laubitz ◽  
T. Matsumura
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
Thermal Expansion ◽  
High Temperature ◽  
Low Temperature ◽  
Theoretical Analysis ◽  
Coefficient Of Thermal Expansion ◽  
Ferromagnetic Metals ◽  
Band Structure Calculations ◽  
Structure Calculations

The thermal conductivity, electrical resistivity, and thermoelectric power of well-characterized, polycrystalline specimens of pure Co have been determined in the temperature range of 90 to 1250 K. Additionally, the measurements of the electrical resistivity have been extended to 1750 K, and the coefficient of thermal expansion measured between 300 and 770 K. The new results are compared with those previously published, and, for the low temperature h.c.p. phase, compared with predictions based on published band structure calculations. Qualitatively, the observed results agree with the predictions, particularly as far as the very unusual temperature variation of the Lorenz function is concerned; quantitative comparisons, however, are impossible, due to the lack of precision in the calculated band structures. The theoretical analysis of the results for the high temperature f.c.c. phase will be given together with that of Ni in Part II.

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