Debye model

About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.

Debye relaxation and 250 K anomaly in glass forming monohydroxy alcohols

Abstract: A previous dielectric, near-infrared (NIR), and nuclear magnetic resonance study on the hydrogen-bonded liquid 2-ethyl-1-hexanol [C. Gainaru et al., Phys. Rev. Lett. 107, 118304 (2011)10.1103/PhysRevLett.107.118304] revealed anomalous behavior in various static quantities near 250 K. To check whether corresponding observations can be made for other monohydroxy alcohols as well, these experimental methods were applied to such substances with 5, 6, 7, 8, and 10 carbon atoms in their molecular backbone. All studied liquids exhibit a change of behavior near 250 K, which is tentatively ascribed to effects of hydrogen bond cooperativity. By analyzing the NIR band intensities, a linear cluster size is derived that agrees with estimates from dielectric spectroscopy. All studied alcohols, except 4-methyl-3-heptanol, display a dominant Debye-like peak. Furthermore, neat 2-ethyl-1-butanol exhibits a well resolved structural relaxation in its dielectric loss spectrum, which so far has only been observed for diluted m...

Size factor and superconducting properties of some transition metal solutions

Abstract: Superconducting primary substitutional solid solutions, consisting of niobium, vanadium or tantalum (column V of the periodic table) alloyed with a metal of column IVA or VIA, show interesting correlations between size of solute and (a) lattice parameter, (b) critical temperature, (c) critical current, (d) coefficient of electronic specific heat, and (e) the Debye characteristic temperature. Solute atoms larger than the matrix atoms increase (a), (b), (c), and (d), but decrease (e). Solute atoms smaller in size decrease (a), (b), (c), and (d), but increase (e). ${T}_{c}$ is found to correlate better with an effective $\frac{e}{a}$ ratio, that contains a sizedependent correction than with the usual $\frac{e}{a}$ ratio. Magnetization studies indicate that these alloys approach an Abrikosov type of behavior when the sample is in powder form. In bulk form hysteresis is influenced by the relative size of solute and matrix atoms.

The defect level and ideal thermal conductivity of graphene uncovered by residual thermal reffusivity at the 0 K limit

Abstract: Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m−1 K−1 due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed “thermal reffusivity”: Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C × e−θ/2T and fitting the Θ–T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m−2 for the studied GF and 43–112 s m−2 for three highly crystalline graphite materials. This uncovers a 16–43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33–299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal–T profile by comparing with those reported for suspended graphene.

Temperature dependence of the mean square relative displacements of nearest-neighbour atoms derived from EXAFS spectra

Abstract: An investigation of the dependence on temperature of the extended X-ray absorption fine structure (EXAFS) above the K-edges of Cu and Co in the metals and above the K-edges of Rb and Sr in the compounds RbCl, SrS, SrF2 and SrCl2 has been performed. For Cu, Co, RbCl and SrS, the values of the correlated mean square relative displacements of nearest-neighbour atoms derived from EXAFS spectra show a good agreement with those calculated from a Debye model. The experimental data obtained are also compared with available data for mean square displacements of the individual atoms calculated from more-refined lattice vibrational models and with Debye-Waller factors used in X-ray diffraction experiments.