Debye Characteristic Temperature Research Articles

Size effect of the resistivity of thin epitaxial gold films

The temperature dependence of the electrical resistivity of thin, epitaxial, and flat (111)-oriented gold films with thickness between 2 and $50\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ is investigated. The quality of these Au films is superior to epitaxial Au films grown on mica, therefore the investigation of well-defined thin films was possible. The experiments are analyzed within the frame of classical size-effect theories of the resistivity. It turns out that for thin films, the characteristic Debye temperature is strongly decreased as compared to the bulk value. In contrast to the more physically motivated approach of Soffer, the original model of Fuchs-Sondheimer describes the experimental data in a physically consistent way.

Single-crystal elastic constants of Fe-15Ni-15Cr alloy

Resonant ultrasound spectroscopy (RUS) and pulse-echo (PE) superposition techniques have been used to determine the three independent elastic-stiffness constants C11, C12, and C44 as a function of temperature for single crystals of 70Fe-15Ni-15Cr alloy. The values of the elastic moduli determined using RUS and PE are in very good agreement within the range of uncertainties. This particular ternary composition of Fe, Ni, and Cr undergoes an fcc-bcc structural phase transformation near 190 K resulting in a low-temperature ferromagnetic phase. The Debye characteristic temperature was determined to be 447 K from PE and 451 K from RUS measurements. The Zener elastic anisotropy A=2C44/(C11−C12) is nearly constant: A=3.53±0.16 in Fe-Ni-Cr alloys with similar compositions. For these alloys, only small variations are observed in the Gruneisen parameter, γ≈2.08, and in the Poisson ratio, v[hkl]=0.293±0.013.

Structural analysis of dynamically synthesized diamonds

Shock wave synthesized diamond and detonation synthesized diamond were discussed in this paper. X-ray diffraction, electron microscopy, Raman spectroscopy, and Fourier-IR spectroscopy were used to study the structural properties of the two dynamically synthesized diamonds. The X-ray diffraction patterns were further analyzed to extract the thermal parameter B, root-mean-square atomic displacement, Debye characteristic temperature, average grain size and microstrain for the two diamonds. Both the two dynamically synthesized diamonds have a cubic conformation and considerable microstrain. Detonation synthesized diamond has a larger lattice parameter, a larger thermal parameter B, a larger microstrain and a smaller grain size than shock synthesized diamond. A size dependence of the thermal parameter B and Debye temperature was also found.

Beryllium’s monocrystal and polycrystal elastic constants

Using resonant-ultrasound spectroscopy, we measured beryllium’s elastic constants for both a monocrystal and a polycrystal. Thus, we consider the monocrystal–polycrystal elastic-constant relationship for hexagonal symmetry. Beside the Cij, we report the Debye characteristic temperature Θ and the Grüneisen parameter γ. We comment on beryllium’s chemical bonding and its remarkably low Poisson ratio.

Low-temperature calorimetric evaluation of aluminum–lithium alloys

Low temperature calorimetric measurements have been made on a series of binary aluminum alloys containing 1–10 at. % lithium. The heat capacity data are analyzed in terms of an electronic and a lattice contribution. Accordingly, the low level of lithium addition yields appreciable changes in the electronic density-of-states at Fermi level and the characteristic Debye temperature of lattice. These results reflect certain degrees of electron localization between aluminum and lithium atoms, providing a fundamental basis for solid solution strengthening in the lightweight materials with great potential in aerospace applications.

Preparation, Structure and Thermal Properties of CuGa5Se8.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation, structure and thermal properties of CuGa5Se8

AbstractThe structural parameters, the axial thermal expansion coefficients and the characteristic Debye temperatures for the order vacancy compound CuGa5Se8 with the chalcopyrite‐related structure, prepared by the Bridgman technique, were determined at different temperatures between 90 and 650 K by the X‐ray diffraction method. The melting point of this compound was defined from the differential thermal analysis data. The anisotropy of thermal expansion in CuGa5Se8 is shown to exist with the coefficients along a‐axis being larger than those along the c‐axis throughout the temperature range studied.

ELASTIC PROPERTIES OF THE Zn SUBSTITUTED ErBa2Cu3O7-δ SUPERCONDUCTOR

Ultrasonic longitudinal and shear velocity in superconducting ErBa 2( Cu 3-x Zn x) O 7-δ (x = 0, 0.01 and 0.05) have been measured using the pulse-echo-overlap method at frequency 5–10 MHz in the temperature range 80–300 K. Longitudinal velocity hysteresis and elastic anomaly were observed in the x = 0 sample. Similar hysteresis was not observed in the x = 0.01 and 0.05 samples. The characteristic Debye temperature and electron–phonon coupling constant were calculated. The absence of hysteresis for longitudinal velocity in the x = 0.01 and 0.05 samples may be due to the spin correlation at the CuO 2 planes which affects the electron–phonon interaction.

High-precision parallel-beam X-ray system for high-temperature diffraction studies

A recently developed Rigaku parallel-beam X-ray diffraction system equipped with a parabolic graded-multilayer mirror in the incident beam and a parallel-slits analyzer in the diffracted beam was used for precision high-temperature diffraction studies. The lattice parameters a and c of α-Al2O3 at room temperature and up to 1473 K were determined with precision in the range of 0.6–7.3×10−5. The thermal expansion coefficients for a and c agreed with literature values to better than 3%. The system was used successfully also to determine the Debye characteristic temperature of Si and to study structural phase transition of LaCoO3 from rhombohedral at room temperature to cubic at 1700 K.

Microstrain effect on thermal properties of nanocrystalline Cu

The nanocrystalline (nc) Cu samples with different microstrains but the same grain size were obtained by annealing a magnetron-sputtered nc Cu specimen. Quantitative X-ray diffraction (XRD) measurements show that with an increment of the microstrain from 0.14 to 0.24% the thermal expansion coefficient (TEC) of crystalline lattice increases by about 12%, the static displacement of atom from the equilibrium position ( B S) increases from 0.47±0.09 to 1.16±0.15 A ̊ 2 , and Debye characteristic temperature ( D) decreases from 307.1±3.1 to 279.2±2.8 K. The microstrain effect on thermal properties in the nc Cu might be attributed to the change in density of grain boundary defects/dislocations. The present investigation demonstrates that the thermal properties of nc materials are determined by not only the grain size but also the microstructure of grain boundaries.

Crystal structure and electrical conductivity correlation in CaTi1−xFexO3−δ system

The structural refinements of CaTi1−xFexO3−δ (x=0 − 0.4) were performed by means of the X-ray data full-profile analysis method on the basis of the orthorhombic perovskite structure (space group Pbnm). The lattice parameters, atomic coordinates, occupancies and equivalent isotropic temperature factors were refined. The characteristic Debye temperature value was determined for the composition x=0.25 by analysis of the temperature dependence of X-ray reflections intensity. Using the structural refinement results, the model of oxygen vacancy formation, ordering and transport under acceptor doping was proposed. The dependence of the ionic conductivity on the iron concentration in CaTi1−xFexO3−δ calculated in the frame of proposed model describes well the experimental data.

The thermodynamic equation for the dissolution of solids in liquids.

A solvation model of a superficial layer on the liquid - solid interface is given. This model is applied for the description of the dissolution of solid compounds in liquids. The superficial layer is supposed as a solid solution of a solvent in a solute of non-stoichiometric composition. It is described within the scope of the Debye model of a solid state. A peculiarity of the model is that the Debye temperature of the solid solution is a function of the partial densities of the solvent and the solute. The solvation effect is taken into account by using one constant - the Gruneisen solvation constant. For the temperature dependence and for the heat of dissolution analytical expressions are obtained. The expressions are functions of the Debye characteristic temperature and the Gruneisen solvation constant of a superficial layer. Thorough comparison with the experiments on the dissolution and the heat of dissolution of the metals in liquid mercury is performed yielding excellent agreement.

High-Temperature Investigation of the Dynamics and Thermodynamics of ZrH-U System by Neutron Scattering

Inelastic neutron scattering (INS) measurements of the vibrational frequencies in δ-Zr hydride containing uranium, ZrH1.6U0.32, have been performed in the range of high temperatures (between 293 and 973 K) at the DIN-2PI time-of-flight spectrometer at the IBR-2 pulsed reactor of JINR, Dubna. From the temperature dependence of the generalized vibrational density of states (GVDS), information on the H potential has been obtained. Also the high frequency limit of lattice vibrations as well as the frequency of optical vibrations have been studied as functions of temperature. Starting from basic properties, the main thermodynamic functions, the characteristic Debye and Einstein temperatures and the total specific heat have been derived.

Thermal Expansion of Gallium and Indium Phosphides: Thermodynamic Evaluation

The thermal expansion coefficient of molten InP was measured between 1331 and 1426 K. The available thermal expansion data for solid InP and GaP were critically evaluated and optimized with the use of heat capacity data. The most reliable data over a wide temperature range were recommended and were used to calculate the Debye characteristic temperature. The results were compared with the data obtained by other methods.

Correlation between bond strength parameters in molten materials exhibiting semiconductor-semiconductor melting behavior

Experimental data on the thermal expansion of molten semiconductors are used to evaluate the Debye characteristic temperature of the melt, the m>Θ2value (characterizing the energetics of the short-range-order structure), and the root-mean-square dynamic displacement of atoms from their equilibrium positions. These bond strength parameters are shown to be correlated with one another. Comparison with earlier data for crystalline materials demonstrates that melting notably reduces the bond strength and changes the vibrational spectrum of the material.

Volume Changes during Melting and Heating of Zinc and Cadmium Tellurides

The method of penetrating γ-radiation is used to investigate the temperature dependence of the density of condensed phases of zinc and cadmium tellurides in the vicinity of the melting point and to determine volume changes during transition from the solid to liquid state. The density of zinc telluride in the liquid phase is investigated for the first time. It is demonstrated that, during melting, the density of both investigated compounds decreases and continues to decrease linearly on heating in the liquid state. It is noted that, in accordance with Regel's classification, zinc and cadmium tellurides melt down by the semiconductor–semiconductor pattern. The volume changes of the investigated compounds during melting are analyzed using the Clausius–Clapeyron equation. The pressure coefficients of the melting temperature of these compounds are estimated, and it is noted that they are positive (dT / dp > 0). The thermal expansion of zinc and cadmium tellurides in the solid and liquid phases is analyzed; the equation of Sirota is used to calculate the characteristic Debye temperatures from which the mean-square dynamic displacements of atoms from the equilibrium position in the structure of condensed phases are determined at the melting point of the investigated compounds.

Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system

The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al70Pd21Tc9 alloy has a face-centered icosahedral quasi-lattice with parameter a=6.514 A. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al70Pd21Tc9 sample is measured in the temperature range 3–30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2–300 K. The electrical resistivity is found to be high (600 µΩ cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (γ=0.24 mJ/(g-atom K2)) and the Debye characteristic temperature (Θ=410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed.

Heat capacity and thermodynamic properties of YBaSrCu3O7-δ in the range 7–300 k

The heat capacity of the high-Tc superconductor YBaSrCu3O7 ‡ was measured by adiabatic calorimetry between 7 and 300 K. The temperature dependence of heat capacity was found to exhibit anomalous behavior at 94 and 255 K. The Debye characteristic temperature was determined to be θD = 369 K at low temperatures. The heat capacity data were used to assess the thermodynamic properties of YBaSrCu3O7-δ in the range 5–300 K.

Analysis of thermodynamic functions of silicon at high temperatures

It is for the first time that the results of experimental studies of variation of the enthalpy and heat capacity of silicon are analyzed within the framework of anharmonic expansion of the Debye model with due regard for the temperature dependence of the characteristic Debye temperature θ(T) in the temperature region above room temperature up to the melting point. The calculation results in a wide range of temperatures 300 ≤T≤ 1400 K are in rather satisfactory agreement with the experimental temperature dependence of the enthalpy variation of the material. However, in the vicinity of the melting point of siliconT m = 1690 K, the experimental points lie above the predicted curve. The additional increment of the enthalpy of silicon in the premelting region, established for the first time in this study, is interpreted within the framework of the Frenkel thermal activation model.

Volume changes during melting and heating of silicon and germanium melts

The temperature dependence of the density of silicon and germanium in the neighborhood of the crystal-melt phase transition is investigated by an improved thermometric method. Changes in volume occurring during transition from the solid to the liquid state are estimated. It is shown that the density increases in the process of crystal-melt phase transition and, accordingly, the specific volume decreases in both silicon and germanium; an increase in pressure noticeably decreases the melting points of both investigated substances. A linear temperature dependence of density in the liquid phase is obtained. The strength characteristics of interatomic bonds are estimated such as the characteristic Debye temperatures and root-mean-square dynamic displacements of atoms from the equilibrium position in the short-range order structure of the melts of the investigated substances. It is shown that the melting process noticeably weakens the cohesive forces between particles and substantially changes the pattern of their oscillation spectrum.