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 Behavior of Thermal Conductivity near the Magnetic Transition Point

Abstract: The anomaly of thermal conductivity at the magnetic transition point observed in certain magnetic crystals was treated theoretically using the correlation function expression for the thermal conductivity The heat conduction by the spin system is shown to be negligible in the vicinity of the transition point The phonon thermal conductivity was studied when the transition temperature is much smaller than the Debye temperature adopting a simple spin-phonon coupling derived by a consideration of the change of energy of the spin system caused by the strain due to a phonon Processes involving creation and annihilation of a phonon as well as scattering were considered, and the anomalous temperature dependence of thermal conductivity at the transition point was understood in terms of the critical scattering of phonons by critical fiuctuations of the energy density of the spin system that is revealed in the specific heat of the spins Cases with more general types of the spin-phonon interaction are briefly discussed (auth)

Elastic constants and Debye temperature of polycrystalline Y1Ba2Cu3O7−x

Abstract: Using ultrasonic methods, the quasi-isotropic elastic stiffnesses of void-containing Y1Ba2Cu3O7−x were determined By a composite-material model, these were corrected to the void-free state. From these, the Debye characteristic temperature was calculated. All the elastic stiffnesses fall well below those of polycrystalline BaTiO3, an approximate crystalstructural building block of Y1Ba2Cu3O7−x. The low apparent stiffness may result from oxygen vacancies, which soften interionic forces. Also, it may result from microcracks, which reduce elastic stiffness without lowering mass density.

Prediction study of structural and elastic properties under the pressure effect of M2GaC (M=Ti,V,Nb,Ta)

Abstract: Using first-principles density functional calculations, the effect of high pressures, up to 20 GPa, on the structural and elastic properties of M2GaC, with M=Ti, V, Nb, and Ta, were studied by means of the pseudopotential plane-waves method. Calculations were performed within the local density approximation to the exchange-correlation approximation energy. The lattice constants and the internal parameters are in agreement with the available results. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s moduli, and Poisson’s ratio for ideal polycrystalline M2GaC aggregates. We estimated the Debye temperature of M2GaC from the average sound velocity. This is a quantitative theoretical prediction of the elastic properties of Ti2GaC, V2GaC, Nb2GaC, and Ta2GaC compounds and it still awaits experimental confirmation.

Pressure-temperature stability studies of FeOOH using X-ray diffraction

Abstract: The Mie-Gruneisen formalism is used to fit a Birch-Murnaghan equation of state to high-temperature (T), high-pressure (P) X-ray diffraction unit-cell volume (V) measurements on synthetic goethite (alpha-FeOOH) to combined conditions of T = 23-250o C and P = 0-29.4 GPa. We find the zero-pressure thermal expansion coefficient of goethite to be alpha0 = 2.3 (+-0.6) x 10-5 K-1 over this temperature range. Our data yield zero-pressure compressional parameters: V0 = 138.75 (+- 0.02) Angstrom3, bulk modulus K0 = 140.3 (+- 3.7) GPa, pressure derivative K0' = 4.6 (+- 0.4), Gruneisen parameter gamma0 = 0.91 (+- 0.07), and Debye temperature Theta0 = 740 (+- 5) K. We identify decomposition conditions for 2alpha-FeOOH --> alpha-Fe2O3 + H2O at 1 - 8 GPa and 100-400oC, and the polymorphic transition from alpha-FeOOH (Pbnm) to epsilon-FeOOH (P21mn). The non-quenchable, high-pressure epsilon-FeOOH phase P-V data are fitted to a second-order (Birch) equation of state yielding, K0 = 158 (+- 5) GPa and V0 = 66.3 (+- 0.5) Angstrom3.

Debye series for light scattering by a multilayered sphere

Abstract: We have derived the formula for the Debye-series decomposition for light scattering by a multilayered sphere. This formulism permits the mechanism of light scattering to be studied. An efficient algorithm is introduced that permits stable calculation for a large sphere with many layers. The formation of triple first-order rainbows by a three-layered sphere and single-order rainbows and the interference of different-order rainbows by a sphere with a gradient refractive index, are then studied by use of the Debye model and Mie calculation. The possibility of taking only one single mode or several modes for each layer is shown to be useful in the study of the scattering characteristics of a multilayered sphere and in the measurement of the sizes and refractive indices of particles.