Debye model

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

Spin-lattice relaxation in some iridium salts I. Relaxation of the isolated (IrCl6)2- complex

Abstract: Spin-lattice relaxation times have been measured at frequencies from 95 to 24 GHz for isolated (IrCl6)2- complexes in (NH4)2PtCl6 and K2PtCl6. The relaxation rate for the ammonium salt can be expressed as a sum of terms corresponding to a direct process, a Raman process and a concentration-dependent process as follows: for the ratio Ir:Pt = c less than about three per cent (f in Hz, T in °K). The value of Δ(similar 65 °K) agrees with the previously measured exchange interaction between nearest-neighbour (IrCl6)2- complexes. At higher values of c, a faster variation than c2 is found. Data for the potassium salt are similar except for the strongly enhanced Raman process, 1/T1 = 35 × 10-2T9. Theoretical estimates for the direct and Raman states indicate that a simple Debye model is not sufficient to explain all experimental data. All data regarding the concentration-dependent process agree with a mechanism in which single complexes cross relax to exchange-coupled clusters of three or more complexes, and relaxation of such clusters is discussed briefly. In particular, exchange-coupled pairs relax much too slowly to affect relaxation of single complexes (see also II).

Thermal resistivity of Si–Ge alloys by molecular-dynamics simulation

Abstract: We explore the ability of molecular-dynamics simulation to elucidate thermal transport in Si–Ge alloys. Simulations using Stillinger–Weber potentials yield values for the thermal resistivity significantly higher than experimental measurements. In agreement with experiment and theoretical predictions, we find that scattering from mass disorder is dominant, with bond disorder and strain effects playing a very minor role. To explore the origins of the large discrepancies with experiment, we use theoretical methods suitable for the limit where point-defect scattering dominates the resistivity. We find that point-defect scattering models based on a Debye spectrum cannot be used to fit our simulations, indicating that high-frequency modes may play an important role in the simulation. The results have important implications for using classical molecular-dynamics simulation to predict properties of alloy materials near and below the Debye temperature.

First-Principles Study of High-Pressure Behavior of Solid beta-HMX

Abstract: A first-principles plane-wave method with an ultrasoft pseudopotential scheme in the framework of the generalized gradient approximation (GGA) was used to calculate the lattice parameters, bulk modulus and its pressure derivative, energy band structures, density of states, phonon density of states, thermodynamic properties, and absorption spectra of solid beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (beta-HMX). The current Study is focused on the thermodynamics and electronic properties that were not reported previously. The bulk modulus and its pressure derivative are also consistent with experimental data and other theoretical results. From the results for the band gaps and density of states, it was found that beta-HMX has the tendency to become a semiconductor with increasing pressure. As the temperature increases, the heat capacity, enthalpy, product of temperature and entropy, and Debye temperature all increase, whereas the free energy decreases. The optical absorption coefficients shift to higher frequencies/energics with increasing pressure. The present Study leads to a better understanding of how energetic materials respond to compression.

Superconducting and Normal State Properties of NiBi3.

Abstract: The electrical resistivity, heat capacity, superconducting upper critical magnetic field and magnetic susceptibility of NiBi 3 have been measured for the polycrystal and needle crystal. The temperature dependence of the resistivity ρ( T ) above the superconducting transition temperature can be explained by the parallel resistor formula. From ρ( T ), using the sum of two Gruneisen-Bloch functions, we have obtained that the lower main value of the Debye temperature is 70 K and the higher one is 300 K. This is compatible with ω E ≡30.6 K and ω D ≡141 K obtained from the heat capacity using the hybrid Einstein-Debye model. We have compared the angular dependence of the critical magnetic field with that of the effective mass model and found an anisotropic mass ratio m ∥ b / m ⊥ b ≈0.17 for the needle (∥ b -axis) crystal. Almost the same value of 0.14 is also obtained from the analysis of ρ( T ).