Debye model

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

Detailed electronic structure studies on superconducting MgB 2 and related compounds

Abstract: Our recent electronic structure studies on series of transition metal diborides indicated that the electron phonon coupling constant is much smaller in these materials than in superconducting intermetallics. However experimental studies recently show an exceptionally large superconducting transition temperature of 40 K in MgB2. In order to understand the unexpected superconducting behavior of this compound we have made electronic structure calculations for MgB2 and closely related systems. Our calculated Debye temperature from the elastic properties indicate that the average phonon frequency is very large in MgB2 compared with other superconducting intermetallics and the exceptionally high Tc in this material can be explained through BCS mechanism only if phonon softening occurs or the phonon modes are highly anisotropic. We identied a doubly-degenerate quasi-two dimensional key-energy band in the vicinity ofEF along -A direction of BZ (having equal amount of B px and py character) which play an important role in deciding the superconducting behavior of this material. Based on this result, we have searched for similar kinds of electronic feature in a series of isoelectronic compounds such as BeB2, CaB2 ,S rB 2 ,L iBC and MgB 2C2 and found that MgB2C2 is one potential material from the superconductivity point of view. We have also investigated closely related compound MgB4 and found that its EF is lying in a pseudogap with a negligibly small density of states at EF which is not favorable for superconductivity. There are contradictory experimental results regarding the anisotropy in the elastic properties of MgB2 ranging from isotropic, moderately anisotropic to highly anisotropic. In order to settle this issue we have calculated the single crystal elastic constants for MgB2 by the accurate full-potential method and derived the directional dependent linear compressibility, Young’s modulus, shear modulus and relevant elastic properties from these results. We have observed large anisotropy in the elastic properties consistent with recent high-pressure measurements. Our calculated polarized optical dielectric tensor shows highly anisotropic behavior even though it possesses isotropic transport property. MgB2 possesses a mixed bonding character and this has been veried from density of states, charge density and

Thermoelectric transport properties of pristine and Na-doped SnSe1−xTex polycrystals

Abstract: SnSe, a "simple" and "old" binary compound composed of earth-abundant elements, has been reported to exhibit a high thermoelectric performance in single crystals, which stimulated recent interest in its polycrystalline counterparts. This work investigated the electrical and thermal transport properties of pristine and Na-doped SnSe1-xTex polycrystals prepared by mechanical alloying and spark plasma sintering. It is revealed that SnSe1-xTex solid solutions are formed when x ranges from 0 to 0.2. An energy barrier scattering mechanism is suitable for understanding the electrical conducting behaviour observed in the present SnSe polycrystalline materials, which may be associated with abundant defects at grain boundaries. The thermal conductivity was greatly reduced upon Te substitution due to alloy scattering of phonons as well explained by the Debye model. Due to the increased carrier concentration by Na-doping, thermoelectric figure of merit (ZT) was enhanced in the whole temperature range with a maximum value of 0.72 obtained at a relatively low temperature (773 K) for Sn0.99Na0.01Se0.84Te0.16.

Thermal conductance of metal–diamond interfaces at high pressure

Abstract: The thermal conductance of interfaces between metals and diamond, which has a comparatively high Debye temperature, is often greater than can be accounted for by two-phonon processes. The high pressures achievable in a diamond anvil cell (DAC) can significantly extend the metal phonon density of states to higher frequencies, and can also suppress extrinsic effects by greatly stiffening interface bonding. Here we report time-domain thermoreflectance measurements of metal-diamond interface thermal conductance up to 50 GPa in the DAC for Pb, Au0.95Pd0.05, Pt and Al films deposited on type 1A natural [100] and type 2A synthetic [110] diamond anvils. In all cases, the thermal conductances increase weakly or saturate to similar values at high pressure. Our results suggest that anharmonic conductance at metal-diamond interfaces is controlled by partial transmission processes, where a diamond phonon that inelastically scatters at the interface absorbs or emits a metal phonon.

The elastic constants of GaAs from 2 K to 320 K

Abstract: The adiabatic elastic constants of GaAs (n type carrier density 1.3*1016 cm-3) have been obtained between 2 K and 320 K from measurements of ultrasonic wave velocities by the pulse superposition technique. One aim has been to compare the results with the somewhat scattered data obtained at room temperature by previous workers: particular attention has been paid to estimation of the overall uncertainty in the elastic constants. At 298 K, C11=1.1841+or-0.0037, C12=0.537+or-0.016 and C44=0.5912+or-0.0018 in units of 1012 dynes cm-2. The Debye temperature (346.8 K) computed from the data extrapolated to 0 K is in excellent agreement with that (346.7 K) derived from low temperature specific heat measurements. The temperature dependence of the elastic constants have been fitted by an anharmonic oscillator model. The force constants and effective charge have been calculated on the basis of a rigid-ion model. The Gruneisen parameter, particle displacement and energy-flux vectors and cross-sections of the Young's modulus and wave velocity surfaces have been compiled.