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Debye model
About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.
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TL;DR: In this article, temperature-dependent polar angular spectra of 4.6 keV neon ions scattered by an Au(110) surface are measured and analyzed by means of a three-particle model with which the scattering cross section is calculated as a function of the angle of incidence.
37 citations
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TL;DR: In this paper, a radial heat flow technique was used to measure the thermal conductivity, k, of polycrystalline UO2 in the range -57° to 1100°C.
Abstract: A radial heat flow technique was used to measure the thermal conductivity, k, of polycrystalline UO2in the range -57° to 1100°C. The technique yielded results with a probable accuracy of ±1.5% and a precision of ±0.1% in the range 50° to 1100°C. Meaningful measurements were limited to 1100°C by Pt-90 Pt10Rh thermocouple instability, although the apparatus was structurally sound to 1400°C. The thermal conductivity data up to 1000°C could be explained on the basis of heat transport by phonons. The thermal resistance, l/k, exhibits a linear temperature dependence from 200° to 100°C, which is expected for an insulator well above the Debye temperature. The slope of the l/k-temperature plot is 0.0223 cm w−1 which is independent of impurity content and is associated with three phonon umklapp processes. The intercept is sensitive to impurity content as indicated by the fact that it was decreased by a decrease in the oxygen/uranium ratio. Between 1000° and 1100°C, there is a slight departure of l/k from linearity which may be due to the onset of an electronic contribution. Near room temperature, UO2 has a maximum in k which is apparently caused by the rapid decrease in specific heat below this temperature.
37 citations
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TL;DR: In this paper, the structural, elastic and electronic properties of Nb 2 SnC under pressure were investigated by using first-principles plane-wave pseudo-potential density functional theory within the generalized gradient approximation (GGA).
37 citations
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TL;DR: In this article, the dielectric properties of fluorocarbon thin films deposited by radio-frequency magnetron sputtering of polytetrafluroethylene were investigated as a function of frequency (0.1 Hz-1 MHz, infrared frequencies).
Abstract: We investigate the dielectric properties of fluorocarbon thin films deposited by radio-frequency magnetron sputtering of polytetrafluroethylene. The dielectric constant and the loss factor are studied as a function of frequency (0.1 Hz-1 MHz, infrared frequencies) and temperature (room temperature to 100 °C). The value of the dielectric constant is 1.8 at optical frequencies, and around 2.3 in the 0.1 Hz–1 MHz range. The background loss factor is around 0.8% in these samples. Two different polarization mechanisms are identified (β and γ relaxations). The γ process dominates the dielectric constant from 0.1 to 1 MHz. In this frequency range the dielectric constant decreases with temperature (about –4% from room temperature to 100 °C). Temperature dependence of the dielectric constant is well described by a simple Debye model (linear variation of the dielectric constant with 1/T). The γ relaxation is tentatively ascribed to C−F bonds (Nμ2=4×10−32 C2 m−1). The β relaxation has a loss peak located at very low frequencies (<0.1 Hz). It leads to an increase of loss below 10 Hz when temperature is increased above 75 °C. The high-frequency part of the β loss peak decreases as ω−0.35. Study of its temperature dependence leads to an activation energy of 0.66 eV.
37 citations
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TL;DR: The Debye temperature, which is the prefactor of the McMillan equation, dominates in determining the superconducting critical temperatures.
Abstract: The pseudopotential-total-energy method is used to calculate the phonon frequency, the electron density of states at the Fermi level, and the electron-phonon coupling constant for the group-IV elements in the metallic \ensuremath{\beta}-Sn structure. For these elements, the normal-state behavior is similar to that found in other simple and transition metals; the phonon frequencies, force constants, and electron-phonon matrix elements increase with increasing average electron density. With use of a semiempirical treatment of the electron-phonon coupling calculated for one phonon wave vector, the superconducting transition temperatures at normal and high pressures are examined. The superconducting transition temperature decreases while the magnitude of its pressure coefficient increases in going to heavier elements. This behavior is in good agreement with experiment. For Si and Ge, the superconducting behavior is similar to that of white tin. Because of competition and compensation between the cutoff in the phonon spectrum and the electron-phonon matrix element, the electron-phonon coupling \ensuremath{\lambda}'s are similar for the three elements. Hence, the Debye temperature, which is the prefactor of the McMillan equation, dominates in determining the superconducting critical temperatures.
37 citations