Debye model

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

Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements

Abstract: Tellurite containing vanadate (50−x)V2O5–xBi2O3–50TeO2 glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi2O3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi2O3 content. The observed results confirm that the addition of Bi2O3 modifier changes the rigid formula character of TeO2 to a matrix of regular TeO3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi2O3 content are more stable than with high Bi2O3 content.

Temperature dependence of electrical and thermal conduction in single silver nanowire.

Abstract: In this work, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K for in-depth understanding of the strong structural defect induced electron scattering. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds from that of bulk silver. The Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. At room temperature, the thermal conductivity is reduced by 55% from that of bulk silver. This reduction becomes larger as the temperature goes down. To explain the opposite trends of thermal conductivity (κ) ~ temperature (T) of silver nanowire and bulk silver, a unified thermal resistivity (Θ ~ T/k ) is used to elucidate the electron scattering mechanism. A large residual Θ is observed for silver nanowire while that of the bulk silver is almost zero. The same Θ ~ T trend proposes that the silver nanowire and bulk silver share the similar phonon-electron scattering mechanism for thermal transport. Due to phonon-assisted electron energy transfer across grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.

Direct simulation of phonon-mediated heat transfer in a Debye crystal

Abstract: A direct simulation of phonon-mediated heat transfer is described and preliminary results are reported. The method is derived from past work in simulating gas-dynamic flow and uses a linear array of cells for modeling a one-dimensional heat transfer problem. Central to the development of the technique is the Debye model for heat capacity of a crystal. The energy equation for this type of solid is presented and a phonon frequency distribution is obtained leading to a simulation technique that naturally takes into account changes in heat capacity. Using the linear array of cells, two fundamental problems are investigated

Electronic structural, elastic properties and thermodynamics of Mg17Al12, Mg2Si and Al2Y phases from first-principles calculations

Abstract: Electronic structures, elastic properties and thermal stabilities of Mg17Al12, Mg2Si and Al2Y have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that Al2Y has the strongest alloying ability and structural stability. The brittle behavior and structural stability mechanism is also explained through the electronic structures of these intermetallic compounds. The elastic constants are calculated, the bulk moduli, shear moduli, Young's moduli and Poisson ratio value are derived, the brittleness and plasticity of these phases are discussed. Gibbs free energy, Debye temperature and heat capacity are calculated and discussed.

Investigation of cohesive energy effects on size-dependent physical and chemical properties of nanocrystals

Abstract: The intrinsic factor to dominate the size-dependent properties of nanocrystals was investigated through applying cohesive energy to determine the physical-chemical properties. With understanding of the nature of the factor, a model for size-dependent melting temperature, Debye temperature, diffusion activation energy, and vacancy formation energy of nanocrystals was established. The accuracy of the developed model was verified by using the available experimental data of gold nanocrystals. It was found that the above properties have the same size-dependent trend which is contributed by the essential effects of surface/volume ratio. The study reveals that the vacancy formation determined by the cohesive energy is the intrinsic factor to dominate the size-dependent physical-chemical properties.