Debye model

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

Anisotropic H c 2 , thermodynamic and transport measurements, and pressure dependence of T c in K 2 Cr 3 As 3 single crystals

Abstract: We present a detailed study of single crystalline K2Cr3As3 and analyze its thermodynamic and transport properties, anisotropic Hc2(T), and initial pressure dependence of Tc. In zero field, the temperature-dependent resistivity is metallic. Deviation from a linear temperature dependence is evident below 100 K and a T3 dependence is roughly followed from just above Tc (~10K) to ~40K. Anisotropic Hc2(T) data were measured up to 140 kOe with field applied along and perpendicular to the rodlike crystals. For the applied field perpendicular to the rod, Hc2(T) is linear with a slope ~–70 kOe/K. For field applied along the rod, the slope is about –120 kOe/K below 70 kOe. Above 70 kOe, the magnitude of the slope decreases to ~–70 kOe/K. The electronic specific heat coefficient γ, just above Tc, is 73 mJ/mol K2; the Debye temperature ΘD is 220 K. As a result, the specific heat jump at the superconducting transition ΔC~2.2γTc. Finally, for hydrostatic pressures up to ~7 kbar, Tc decreases under pressure linearly at a rate of –0.034K/kbar.

Thermoelastic properties of MgSiO 3 perovskite using the Debye approach

Abstract: MgSiO 3 perovskite is shown to be a Debye-like mineral by the determination of specific heat, C v , entropy, S, and thermal pressure, Delta P Th , using the Debye theory up to 1800 K. Sound velocities and bulk moduli at ambient conditions published by Yeganeh-Haeri were used to find the ambient acoustic Debye temperature, Theta ac D . The variation of Theta ac D with T was assumed to be a curve parallel to the Theta ac D vs. T curves previously found for Al 2 O 3 , MgO, and MgSiO 3 , enabling Theta ac D (T) to be given up to 1800 K. To determine C p , the thermal expansivity, alpha , and the isothermal bulk modulus, K T , are needed. After considering several sets of alpha (T), the alpha (T) data of Funamori and his colleagues were chosen. Using the ambient K T and the values of (theta K T /theta T) P vs. T reported by Jackson and Rigden, K T (T) up to 1800 K was found. Then C P (T) up to 1800 K was found assuming quasiharmonicity in C v . The data behind the C P (T) calculation are also sufficient to find the Gruneisen parameter, gamma (T), and the Anderson-Gruneisen parameters, delta T and delta S , up to 1800 K. The value of q = (theta ln gamma /theta ln V) T was found, and with gamma and rho , Delta P Th vs. V and T was determined. The three sound velocities, v s , v p , and v b = K (sub s/rho ) , were then determined to 1800 K. From v s and v p , Poisson's ratio and the isotropic shear modulus, G, were found to 1800 K. MgSiO 3 perovskite is one of a small, select group of Debye-like minerals for which thermoelastic properties and the equation of state (EOS) are calculable from acoustic data.

Structural behavior of Pd40Cu30Ni10P20 bulk metallic glass below and above the glass transition

Abstract: The thermal behavior of the structure of Pd40Cu30Ni10P20 bulk metallic glass has been investigated in situ through the glass transition by means of high-temperature x-ray synchrotron diffraction. The dependence of the x-ray structure factor S(q) of the Pd40Cu30Ni10P20 glass on temperature follows the Debye theory up to the glass transition with a Debye temperature θ=296 K. Above the glass transition temperature Tg, the temperature dependence of S(q) is altered, pointing to a continuous development of structural changes in the liquid with temperature. The atomic pair correlation functions g(r) indicate changes in short-range-order parameters of the first and the second neighborhood with temperature. The temperature dependence of structural parameters is different in glass and in supercooled liquid, with a continuous behavior through the glass transition. The nearest-neighbor distance decreases with temperature, changing the slope at Tg. The interatomic distances of higher coordination shells expand analogo...

Melting of iron and other metals at earth's core conditions: A simplified computational approach

Abstract: In order to study melting of metals at high pressure, we propose a different method which can be thought of as a generalization of the well-known Lindemann law. One essential interesting feature is that neither the Debye temperature nor the Gr\"uneisen coefficient are used in the theory. We find that the method based on first-principles calculations can be used to model the pressure dependence of the melting properties of metals very well. Predictions of the melting along the principal Hugoniot are calculated for Cu and Ta. In the case of Fe, the melting temperature is calculated at geophysically interesting pressures.

Phonon spectra and vibrational mode instability of Mg C Ni 3

Abstract: This paper reports a detailed and systematic lattice dynamical calculation of the newly discovered intermetallic superconductor $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ by using a lattice dynamical model theory based on pairwise interactions under the framework of the rigid ion model. The results bring out the anomalous vibrational mode instability in the phonon dispersion curves and phonon density of states of $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$. The calculated phonon dispersion curves and phonon density of states are in good agreement with the measured and density functional theoretical (DFT) data. The study also illustrates the contradicting results on the magnitude of phonon frequencies due to Mg atoms and the region of the unstable modes in the Brillouin zone of the previously computed two DFT results. The present study on DOS has enabled an atomic level understanding of the phonon density of states. The phonon density of states has been used to compute the specific heat at constant volume. The Debye temperature and temperature-dependent vibrational amplitudes of the different species are also reported. The present calculation suggests that the superconductivity in $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ is governed by the BCS mechanism.