Topic
Debye model
About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.
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TL;DR: It is found, in agreement with full multiple-scattering calculations, that forward focusing is a fundamental feature of ARPEFS and that curved-wave corrections are essential for quantitative results.
Abstract: We present a theory for photoelectron scattering in the 100--1000 eV energy range designed to simulate experimental measurements of angle-resolved photoemission extended fine structure (ARPEFS) from ordered surfaces. The zero-order problem of photoabsorption in the solid is treated first, followed by a scattering problem which incorporates the scattering ion cores in a perturbation series (cluster expansion). The dynamics of core-hole relaxation are discussed, but the dynamical effects are shown to be small. The Taylor-series magnetic-quantum-number expansion is used for the curved-wave, multiple-scattering equations. We argue that a velocity-dependent surface barrier gives primarily an inner potential shift, with no clear evidence for surface electron refraction. Analytic formulas for aperture integration are derived and thermal averaging in a correlated Debye model is extended to multiple scattering. Reasonable values for nonstructural parameters in the theory are shown to give very good simulations of the experimental ARPEFS measurements from c(2\ifmmode\times\else\texttimes\fi{}2)S/Ni(001) in contrast to previous theoretical calculations. We find, in agreement with full multiple-scattering calculations, that forward focusing is a fundamental feature of ARPEFS and that curved-wave corrections are essential for quantitative results. Since the scattering path-length difference is not appreciably altered by forward scattering, the ARPEFS oscillation frequency is equal to the geometrical path-length difference plus a small potential phase shift, but the amplitude and constant phase of the oscillations cannot be predicted by theories based upon single-scattering or plane-wave approximations.
62 citations
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TL;DR: In this paper, the structural, elastic, electronic properties and Debye temperature of Ni 3 Mo binary compound under pressure are investigated with the help of first principles method based on density functional theory.
62 citations
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TL;DR: In this paper, a spinel was sputter deposited using a series of oxygen partial pressures and electrical resistivity versus temperature and thermopower versus temperature measurements at each oxygen partial pressure were made.
Abstract: Mn1.56Co0.96Ni0.48O4 spinel was sputter deposited using a series of oxygen partial pressures. Electrical resistivity versus temperature and thermopower versus temperature measurements at each oxygen partial pressure were made. The variations of the thermopower and resistivity with oxygen partial pressure are consistent with a change in the ratio of Mn3+to Mn4+ cations, which occurs due to changes of oxygen content of the material. The weak temperature dependence of the thermopower indicates small polaron hopping is the charge transport mechanism. Combining the models of Mott and Schnakenberg to analyze the transport data, we find that the Debye temperature (or frequency) is an increasing function of the oxygen partial pressure used during sputtering. The calculated shift in the Debye frequency from the resistivity is consistent with the observed shift in the fundamental infrared active lattice vibrations from Fourier transform infrared spectroscopy and Raman spectroscopy.
62 citations
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TL;DR: Experimental results are in good agreement with theoretical calculations and Static and dynamic effects to the local disorder have been separately determined and compared with the results of previous studies.
Abstract: Anharmonic contributions to the pair potential of near-neighbor interactions of crystalline and amorphous germanium have been determined by temperature-dependent x-ray absorption fine structure measurements. The measurements have been carried out at the K edge of Ge in the temperature range 77\char21{}450 K and analyzed by the cumulant method. In c-Ge the temperature dependence of the first four cumulants has been determined for the first three coordination shells. The radial distribution function of the nearest-neighbor atoms has been found Gaussian in the examined temperature range; the second and third shell distance distributions show a symmetric but non-Gaussian behavior even below the Debye temperature. Cumulants have been related to the force constants of the effective pair potential. The harmonic contribution to thermal disorder has been extracted from the second cumulant for each coordination shell and compared with the mean square relative displacements calculated by harmonic models of lattice dynamics; experimental results are in good agreement with theoretical calculations. In amorphous germanium the first shell radial distribution function is asymmetric even at the lowest temperatures. Static and dynamic effects to the local disorder have been separately determined and compared with the results of previous studies.
62 citations
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TL;DR: The physical properties of the σ-phase in Fe-Cr and Fe-V alloy systems have been investigated both with experimental and theoretical methods as mentioned in this paper, and the following questions relevant to the issue have been addressed: identification of σ and determination of its structural properties.
Abstract: This review addresses the physical properties of the σ-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental—mostly with the Mossbauer spectroscopy—and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of σ and determination of its structural properties, kinetics of α-to-σ and σ-to-α phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.
62 citations