Debye model

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

On the heat capacities of M2AlC (M=Ti,V,Cr) ternary carbides

Abstract: In this paper, we report on the heat capacities cp of bulk polycrystalline samples of Ti2AlC, V2AlC, and Cr2AlC in the 3–260K temperature range. Given the structural and chemical similarities of these compounds it is not surprising that the cp’s and their temperature dependencies were quite similar. Nevertheless, at all temperatures the heat capacity of Cr2AlC was higher than the other two. The density of states at the Fermi level were 3.9, 7.5, and 14.6(eVunitcell)−1 for Ti2AlC, V2AlC, and Cr2AlC, respectively. The results obtained are analyzed using the Debye and Einstein model approximations for cp. Good description of cp is obtained if one assumes that nine phonon modes vibrate according to the Debye model approximation whereas the remaining 3 of 12 modes expected for M2AlC formula unit fulfill an Einstein-like phonon vibration pattern. Debye temperatures θD describing acoustic phonon and Einstein temperature θE describing optical phonon contributions have been estimated for the studied compounds. The...

Electronic transport in Cd–Yb and Y–Mg–Zn quasicrystals

Abstract: Electronic transport properties of the stable binary Cd5.7Yb quasicrystal and a quasicrystal in the Y–Mg–Zn family is presented. Electrical conductivity in these systems is an order of magnitude higher than other quasicrystals, resulting in larger thermal conductivity values due to enhanced electronic contributions (λE=L0σT). Room temperature Hall measurements provide a charge carrier density of 2.3×1021 and 3.1×1020 cm−3 in Cd5.7Yb and Y–Mg–Zn, respectively, indicating these materials have a higher carrier concentration and are better conductors than other quasicrystalline counterparts. Thermoelectric power in both Cd5.7Yb and Y–Mg–Zn have relatively small magnitudes (16 and 8 μV/K, respectively). Despite many similarities between these two systems, low temperature specific heat reveals a low Debye temperature in Cd5.7Yb(140 K) while the Debye temperature of Y–Mg–Zn and other quasicrystals is at least twice as large. Consequences of the electrical transport in these systems will be discussed.

The Fokker-Planck-Langevin model for rotational Brownian motion. II. Comparison with the extended rotational diffusion model and with observed infrared and Raman band shapes of linear and spherical molecules in fluids

Abstract: A detailed comparison of two extensions of the Debye model for molecular reorientation in liquids, Gordon’s extended J‐diffusion model and the rotational Fokker–Planck–Langevin model, is presented It is shown that the two models, although they represent very different physical pictures of rotational dynamics in fluids, lead to remarkably similar reorientational correlation functions, memory functions, correlation times and spectral densities Only for values of the angular momentum correlation time appropriate to low density fluids do the two models give significantly different results, but the validity of the FPL model is questionable in this region The results of an infrared study of the ν3 band of N2O in N2O/O2 along the coexistence curve from 105–153 K, and in N2O/N2 along the 80 bar isobaric line from 100–300 K are presented The reorientational correlation functions from these measurements, and from earlier infrared studies of CO/N2 and Raman studies of CF4 and N2O liquids are compared with correl

Size and temperature dependence of the mössbauer debye waller factor of iron microcrystals

Abstract: Iron microcrystal ranging in size from 70 to 450 A have been investigated by the Mossbauer effect. There is, compared to the bulk value, a small enhancement of the magnetic field at the site of the nucleus of about 1% which can be interpreted as due to the demagnetisation field of the microcrystals and their geometric arrangement. The observed drastic size and temperature dependent lowering of the Debye Waller factor cannot be explained by a change of the Debye temperature of the microcrystals. Two different models are proposed to explain the effect.