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Showing papers on "Debye model published in 1982"


Journal ArticleDOI
TL;DR: In this paper, the authors provide numerical and graphical information about many physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material, including properties of the material itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage.
Abstract: This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

2,115 citations


Journal ArticleDOI
TL;DR: In this article, a model that uses available elastic, structural, and spectroscopic data on minerals has been used to predict the thermodynamic functions Cv (heat capacity), S (entropy), E (internal energy), and F (Helmholtz free energy).
Abstract: In previous papers in this series, a model that uses available elastic, structural, and spectroscopic data on minerals has been used to predict the thermodynamic functions Cv (heat capacity), S (entropy), E (internal energy), and F (Helmholtz free energy). In this paper, four applications to problems of current geochemical and geophysical interest are presented: (1) interpretation of complex trends of calorimetric data; (2) calculation of phase equilibria; (3) calculation of oxygen-isotopic fractionation factors; and (4) estimation of the effect of pressure on thermodynamic functions. The model demonstrates that trends in high-temperature thermodynamic properties of silicates are determined by the position and relative numbers of high-frequency modes, generally antisymmetric (Si, Al)-O stretching modes. The position of these modes varies systematically with degree of polymerization of tetrahedra, and therefore high-temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition. Trends at low frequency are much more complex because the low-frequency optic modes that most strongly influence the low-temperature thermodynamic functions depend in a complex way on the size, coordination, and mass of cations and various polyhedra in the minerals. The heat capacity curves of kyanite, andalusite, and sillimanite and of quartz, coesite, and stishovite show crossovers that cannot be explained by Debye theory, which accounts only for acoustic mode behavior, but can be explained by the model spectra proposed because proper account is taken of the changing low- and high-frequency optic modes upon polymorphic transformations. The proposed model is sufficiently accurate that phase equilibrium problems can be addressed: the quartz-coesite-stishovite equilibrium curves, the kyanite-andalusite-sillimanite triple point, and the breakdown of albite to jadeite-plus-quartz are cited as specific examples. For each example, predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally. The calculated slopes are sensitive to spectroscopic parameters, particularly to the distribution of optic modes in the far infrared; this sensitivity is discussed in detail for the albite breakdown reaction. The model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated. A simple set of ‘rules’ for generating hypothetical spectra of 18O minerals from measured spectra of the 16O forms is given. Reduced partition functions are calculated for 13 minerals. At 298°K the model values of reduced partition function, 1000 ln α, of these minerals decrease in the order quartz > calcite ≳ albite > muscovite > clinoenstatite ≈ anorthite > diopside > pyrope > grossular > zircon > forsterite > andradite > rutile, in good agreement with experimental data. At 1000°K the first six minerals show small crossovers so that the order becomes calcite, muscovite ≈ albite, quartz, anorthite, and clinoenstatite; the differences in 1000 ln α at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends. The model clearly defines the region in which the fractionation factors do not follow a 1/T² trend and should be useful for extrapolation of experimental data to low temperatures. Finally, a modified Gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression, and thermodynamic properties to 1000 kbar, 1000°K, are given for nine minerals. At 1 Mbar, the predicted decrease in entropy at 298°K ranges from 54% (of the 1-bar value) for periclase to 25% for stishovite.

292 citations


Journal ArticleDOI
TL;DR: The dc conductivity of vanadium tellurite glasses of compositions in the range 50 to 80 mol% V2O5 has been measured in the temperature region 77 to 400 K as mentioned in this paper.
Abstract: The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V2O5 has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V2O5 content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v0. Adiabatic hopping is indicated for v0∼1011 Hz, however this value leads to unreasonably low value for the Debye temperature θD, and higher values for v0∼1013 hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V2O5TeO2 glasses. The low temperature data (< 100 K) can be fitted to Mott's variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy.

183 citations


Journal ArticleDOI
TL;DR: In this paper, phonon dispersion curves of black phosphorus are calculated using the force constant model, in which the valence force model is assumed for intralayer interatomic interactions and the axially symmetric force model for interlayer ones.

85 citations


Journal ArticleDOI
TL;DR: In this paper, the skeletal heat capacity of linear macromolecules is shown to be best represented by only two vibrations per chain atom, and the experimental heat capacities for these analyses were collected in the ATHAS data bank.
Abstract: Automatic computer programs are developed to calculate one- two-, and three-dimensional Debye functions. Prior tables of these functions are critically reviewed. Also, strategies are derived to calculate Debye temperatures from heat capacities. Both, simple three-dimensional Debye analyses and Tarasov analyses were carried out on 35 linear macromolecules. The experimental heat capacities for these analyses were collected in the ATHAS data bank. It is shown that the skeletal heat capacity of linear macromolecules is often best represented by only two vibrations per chain atom. For most of the all-carbon chain macromolecules the intramolecular skeletal heat capacity can be given by Cvs=D1[520 (28/MW)1/2] whereMW is the molecular mass andD1 represents the one-dimensional Debye function. Polyoxides show a higher intramolecular theta temperature, but a lower intermolecular theta temperature. Double bonds and phenylene groups in the chain increase the intramolecular theta temperature.

64 citations


Journal ArticleDOI
R. Reineker1, H. Morawitz1
TL;DR: In this article, the temperature dependence of the optical linewidth of an impurity imbedded in a glassy matrix is investigated and the model hamiltonian couples the impurity to two-level systems (TLSs) characteristic for the glassy state and the TLSs to acoustic phonons of the matrix.

55 citations


Journal ArticleDOI
TL;DR: In this paper, a Debye model of disorder was employed in the EXAFS analysis of a highly dispersed Pt/SiO2 catalyst to determine the temperature dependence of atomic structure in the very small supported clusters.
Abstract: A temperature sequence of EXAFS measurements was carried out on a highly dispersed Pt/SiO2 catalyst to determine the temperature dependence of atomic structure in the very small supported clusters. A one‐shell EXAFS model was fit to the first neighbor oscillations in the catalyst data to determine bond lengths and relative thermal motion (disorder) for an average cluster environment. A Debye model of disorder was employed in the EXAFS analysis. The disorder measured for the catalyst was determined to be 1.3 to 2 times the value determined for bulk Pt over all temperatures. Asymmetry of the radial distributions of nearest neighbors in the largely surface coordinated clusters and the increased atomic disorder lead to underestimates of the nearest‐neighbor distance R1 at higher temperatures. The apparent bond distance contraction with temperature is manifest in the data as a retardation in the phase of the first neighbor oscillations. It is demonstrated that model EXAFS functions employing asymmetric interatomic pair potentials (such as the Morse potential) exhibit very similar bond distance contractions to the catalyst data while maintaining similar estimates for the disorder. Finally, a two‐shell EXAFS model was fit to the catalyst data to separately determine the motion of the surface coordinated atoms in the small metal clusters.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported measurements of the thermal expansion of quartz both parallel and perpendicular to the trigonal axis, at temperatures between 17 and 30K, between 575 and 85K, and a 283K.
Abstract: Reports measurements of the thermal expansion of quartz both parallel and perpendicular to the trigonal axis, at temperatures between 17 and 30K, between 575 and 85K, and a 283K These measurements confirm the qualitative inadequacy of the SiO4 tetrahedral tilt model Together with other thermodynamic data, the results are used to derive Gruneisen functions gamma perpendicular to (T) and gamma /sub ///(T) for temperatures up to 923K gamma perpendicular to (T), gamma /sub ///(T) and the heat capacity are analysed to give the moments ( omega n) of the vibrational frequency distribution, the equivalent Debye temperature theta D(n) and the Gruneisen functions gamma perpendicular to (n) and gamma /sub ///(n) These can be used to estimate various crystal properties For the equilibrium static lattice, the energy and lattice constants are respectively: EL=-1876+or-5 kJ mol-1; aL=4875+or-0005 AA; cL=5380+or-0005 AA The temperature variation of the Gruneisen functions is discussed in the light of available spectroscopic data, and the positive expansion of alpha -quartz is attributed to high values of normal mode Gruneisen parameters in the upper parts of the acoustic branches and in some of the lower optical branches

46 citations


Journal ArticleDOI
P. Andonov1
TL;DR: In this paper, a structural analysis of amorphous, viscous and liquid selenium was performed using X-ray diffraction in the wave vector region 0 A and over a large range of temperature (78 to 683 K).
Abstract: In this work results are presented of various experiments involving the amorphous form of massive selenium, and a structural study performed by X-ray diffraction in the wave vector region 0 A and over a large range of temperature (78 to 683 K). At first, to suppress doubts which subsist in spite of several published reports concerning amorphous material, we examine in detail the dependences of the physical properties and the structural variations on applying a uniaxial compression at 293 K in the metastable form. Comparisons between deformed or non-deformed materials (D a-Se or ND a-Se) are made using measurements of density, longitudinal sound velocity, differential thermal analysis, small angle scattering and careful analysis of the structure factor J(K). The information gained on the structural evolution with temperature is discussed. The variation of Debye temperature, determined from measures of sound velocity between 78 K and 300 K, permits us to calculate the thermal attenuation. In amorphous selenium, the Debye hypotheses are not valid. A temperature variation has no influence on the structure of the amorphous phase. In the viscous phase a slow evolution is observed but only in the liquid phase does a real change of J(K) appear. A disordered chain model is retained to describe the structure of the molecule in amorphous, viscous and liquid selenium. The elementary triangle of the selenium lattice remains constant. The intramolecular deformation is due to a limited variation of the dihedral angle which is random in sign. The limits of variation are reduced weakly by a uniaxial compression and also by an increase of temperature but only for T>Tg; the deformed chains approximate to the hexagonal arrangement. The presence of prolate ellipsoidal voids included between the chains explains the difference in density between the crystallized hexagonal Se and the amorphous material. Finally several simulated models are compared with the experimental J(K) measured at different temperatures. The same uncertainty always remains in the description of the models and the explanation of experiments as a result of the impossibility of separating the two contributive intra and intermolecular disorders.

45 citations


Journal ArticleDOI
TL;DR: The low-temperature specific heat (CP) and magnetic susceptibility (χ) for the amorphous alloys Fe90Zr10, Co90ZR10, and Co86Zr14 are presented in this paper.
Abstract: The low‐temperature specific heat (CP) and magnetic susceptibility (χ) for the amorphous alloys Fe90Zr10, Co90Zr10, and Co86Zr14 are presented. A very large linear contribution to CP combined with a sharp decrease in χ below about 60 K show Fe90Zr10 to have spin‐glass or spin‐cluster glass behavior at low temperatures. The Co‐based alloys show no deviations from true ferromagnetic behavior at low temperatures. Values of the Debye temperature for all three alloys and the electronic density of states for the Co‐based alloys are obtained.

45 citations


Journal ArticleDOI
TL;DR: In this paper, the elastic stiffness tensor of the chalcopyrite structure crystal CdGeAs2 has been obtained between 4.2K and 290K from measurements of ultrasonic wave velocities by the pulse echo overlap technique.
Abstract: The components (at 290K C11=9.45, C12=5.96, C13=5.97, C33=8.34, C44=4.21, C66=4.08, in units of 1010 N m-2) of the elastic stiffness tensor of the chalcopyrite structure crystal CdGeAs2 have been obtained between 4.2K and 290K from measurements of ultrasonic wave velocities by the pulse echo overlap technique. These elastic moduli, used to calculate the bulk and Young's moduli, Poisson's ratio and the Debye temperature ( theta Del=257+or-2K), define the elastic behaviour of an AIIBIVC2V chalcopyrite. Measurements of the hydrostatic pressure dependence of the ultrasonic wave velocities up to about 108 Pa have been used to obtain the pressure derivatives of the elastic moduli at room temperature. Negative values of delta C44/ delta P and delta (1/2(C11-C12))/ delta P show that the long-wavelength transverse q(110), e(110); q(100), e(001) and q(001), e(100) acoustic phonon modes soften under high pressure. Expressions for the acoustic mode Gruneisen parameters in the long-wavelength limit in the anisotropic continuum model have been developed for 4/mmm Laue group tetragonal crystals; the calculated Gruneisen parameters for CdGeAs2 establish quantitatively an anomalous decrease of the frequencies of certain shear modes. The high pressure transition at 60 GPa may be associated with weakening of the interatomic binding forces against shear distortion.

Journal ArticleDOI
TL;DR: In this article, it was shown that there is a linearity between the thermal pressure P TH and T between the Debye temperature θ and some high temperature T ∗.

Journal ArticleDOI
TL;DR: In this article, the electronic structure of the Ni-Zr system based on photoemission, susceptibility and specific heat measurements was studied, and it was shown that the contribution of Ni atoms to the electronic density of states at the Fermi level is small or negligible, while that of Zr atoms is similar to a pure metal.
Abstract: The authors present a study of the electronic structure of the Ni-Zr system based on photoemission, susceptibility and specific heat measurements. Their results show that the band structure can be understood in a relatively simple model, which has been partially presented before. For concentrations below 50 at.%Ni the contribution of Ni atoms to the electronic density of states at the Fermi level n(EF) is small or negligible, while that of Zr atoms is similar to a pure metal. NiZr2 is a superconductor with Tc=1.62K; it also presents an atypical Debye temperature, which is related to soft modes, and a high electronic specific heat, which is attributable to the occurrence of a strong electron-phonon coupling. For concentrations between about 50 and 27.5% Zr, due to the widening of the Ni d band, the Ni contribution to n(EF) becomes appreciable and increases moderately with the Ni content. For concentrations higher than 72.5 at.%Ni, this contribution increases rapidly and a large enhancement factor to the susceptibility is noticed. These properties can be related to the atomic structure, in particular the number of Ni neighbours of the Ni atom.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the electron spin-lattice relaxation time T1 of the (4Fe-4S) ferredoxin from Bacillus stearothermophilus is studied in the range 1.2 to 40 K.
Abstract: The temperature dependence of the electron spin–lattice relaxation time T1 of the (4Fe–4S) ferredoxin from Bacillus stearothermophilus is studied in the range 1.2 to 40 K. This dependence is similar to that observed for the (2Fe–2S) ferredoxin from Spirulina maxima and can be interpreted with the same relaxation processes [J.P. Gayda, P. Bertrand, A. Deville, C. More, G. Roger, J.F. Gibson, and R. Cammack, Biochim. Biophys. Acta 581, 15 (1979)]. In particular, between 4 and 15 K, the data are well fitted by a second‐order Raman process involving three‐dimensional phonons, with a Debye temperature of about 60 K (45 cm−1). This would give an estimation of the highest frequency of the vibrations which can propagate through the three‐dimensional proteinic medium. In the highest temperature range (T≳30 K) the results are interpreted with an Orbach process involving an excited level of energy 120 cm−1. This process could be induced by the localized vibrations of the active site. Finally, these results are compared to those recently reported for some hemoproteins [H.J. Stapleton, J.P. Allen, C.P. Flynn, D.G. Stinson, and S.R. Kurtz, Phys. Rev. Lett. 45, 1456 (1980)]. Below 15 K, the temperature dependence of T1 for these samples is similar to that observed for the iron–sulfur proteins and may be interpreted in the same way. Our interpretation is compared to the fractal model proposed by Stapleton et al.

Journal ArticleDOI
TL;DR: In this paper, the authors used the attenuation of the specular peak in the surface temperature range from 20 to 300 K to derive the mean square displacement of surface atoms, perpendicular to the (0001) graphite plane.

Journal ArticleDOI
TL;DR: The specific heat of the ternary semiconducting compounds CuGaSe2, CuGaTe2, and CuInTe2 was determined experimentally in a temperature region within 2 and 30 K as discussed by the authors.
Abstract: The specific heat Cv of the ternary semiconducting compounds CuGaSe2, CuGaTe2, and CuInTe2 is determined experimentally in a temperature region within 2 and 30 K. From the results the Debye temperatures and standard entropies are calculated. By dividing Cv into a Debye and two Einstein contributions the approximate shape of the low frequency phonon modes is estimated. Die spezifische Warmekapazitat CV der ternaren halbleitenden Verbindungen CuGaSe2, CuGaTe2 und CuInTe2 wird experimentell in einem Temperaturbereich von 2 bis 30 K bestimmt. Aus den Mesergebnissen werden Debyetemperaturen und Standardentropien berechnet. Durch Aufteilen von Cv in einen Debyeteil und zwei Einsteinteile last sich der genaherte Verlauf der niedrigfrequenten Phononenmoden abschatzen.

Journal ArticleDOI
TL;DR: The elastic constants of the Ta-W system were determined between 4.2 and 300 K as discussed by the authors, and anomalous behavior was detected in the temperature dependence of the shear constant c44 near the critical composition of about 50% W. This anomaly is attributed to certain topoligical changes in the Fermi surface of the alloys near a critical composition.
Abstract: The elastic constants of the Ta‐W system were determined between 4.2 and 300 K. Anomalous behavior was detected in the temperature dependence of the shear constant c44 near the critical composition of about 50% W. This anomaly is attributed to certain topoligical changes in the Fermi surface of the alloys near the critical composition. The Debye temperature for the alloys was calculated from the elastic constants.

Journal ArticleDOI
TL;DR: In this paper, the vibrational spectra of V2+ and Cr3+ impurities in MgO phonons were used to determine the pressure dependences of the energies of phonons at several critical points of the Brillouin zone.
Abstract: Vibronic spectra of V2+ and Cr3+ impurities in MgO have been used to determine the pressure dependences of the energies of MgO phonons at several critical points of the Brillouin zone to more than 100 kbar at 90 and 295 K. From these data, approximate densities of states for MgO at 100 and 500 kbar and vibrational partition functions were constructed, and contributions to the constant-volume heat capacity, entropy, internal and free energies, and the Debye temperature were calculated. Argon was successfully used as a nearly hydrostatic pressure medium for the measurements at 90 K to 102 kbar.

Journal ArticleDOI
TL;DR: The thermal expansion coefficients of a number of phenacites [Be2SiO4, β•Si3N4 and β•Sialon, α•LiAlSiO 4, Zn2NiO4 and CdAl2O4] at temperatures at and above the Debye temperature were analyzed in terms of the thermal Gruneisen parameter.
Abstract: The thermal expansion coefficients of a number of phenacites [Be2SiO4, β‐Si3N4, β‐Sialon, α‐LiAlSiO4, Zn2SiO4, CdAl2O4, and Zn2GeO4] at temperatures at and above the Debye temperature are analyzed in terms of the thermal Gruneisen parameter γ. The phenacites have γ values intermediate between adamantine crystals and quartz. Values of γ between 0.3 and 0.7 are found. A useful correlation exists between γ and the average volume per anion bond W. Values of γ approaching zero occur for sufficiently large values of W.

Journal ArticleDOI
TL;DR: In this article, the authors measured the dielectric constants of highly purified ethylene glycol/water mixtures as functions of temperature and mixture ratio, and found that these mixtures can support fields greater than 15 MV/m for periods exceeding a millisecond.
Abstract: Measurements of the (complex) dielectric constant, intrinsic time constant, and electrical breakdown strength of highly purified ethylene glycol/water mixtures as functions of temperature and mixture ratio are presented. Over the frequency range from 0.5 to 108 MHz, the dielectric constant is found to be well represented by a simple Debye model. When cooled to near their freezing points, these mixtures have dielectric constants of the same order as pure water (∼80) but with intrinsic time constants at least an order of magnitude greater than water. The mixtures are found to support fields greater than 15 MV/m for periods exceeding a millisecond. The observed high‐voltage decay is nonsimple due to the phenomenon of charge injection. The ability to sustain high fields for millisecond time scales suggests the use of such mixtures as the dielectric in the pulse forming lines of large‐pulse power machines.

Journal ArticleDOI
TL;DR: In this article, the specific heat of an annealed powder sample in a 3He-cryostat in the temperature range 2-20 K and in a liquid helium cryostat, in both cases using helium as heat exchange gas, was measured.
Abstract: Fe2P (space group P2m) is a highly anisotropic, metallic ferromagnet with the spontaneous magnetization directed parallel to the c-axis. The ferromagnetic transition at Tc = 217 K is of first order and accompanied by a sudden change in lattice parameters. In order to study the ferromagnetic transition we have measured the specific heat of an annealed powder sample in a 3He-cryostat in the temperature range 2-20 K and in a liquid helium cryostat in the range 80-300 K, in both cases using helium as heat exchange gas. The low temperature measurements give an electronic part of the specific heat characterized by γ = 24 mJ/K2 · mole and a lattice part with a Debye temperature of Θ = 420 K at the lowest temperatures. Effects of helium adsorption on the powder sample (surface area ≈ 0.5 m2) were accounted for. The ferromagnetic transition is only noticeable through a sharp, symmetric peak at 217 K (width 0.6 K) raising above a smooth background. The corresponding entropy change is ΔS ≈ 0.2 J/K · mole (≈ 0.02 R) in reasonable agreement with an entropy change calculated from Clapeyrons equation.

Journal ArticleDOI
H. Nasu1, Naohiro Soga1
TL;DR: In this paper, the electric conductivity was measured from 150 K to 300 K on sodium-iron phosphate glasses having the composition of X Fe 2 + Y O 3. (45 − X )Na 2 O·55P 2 O 5 (X = 0−45, Y = 0.09−0.98) in which ionic and/or electronic conduction may be possible.
Abstract: The electric conductivity was measured from 150 K to 300 K on sodium-iron phosphate glasses having the composition of X Fe 2 + Y O 3 . (45 − X )Na 2 O·55P 2 O 5 ( X = 0−45, Y = 0.09–0.98) in which ionic and/or electronic conduction may be possible. The conduction mechanism was examined on the basis that the activation energy of electronic conducting glasses is generally lower than that of ionic conducting glasses, and the relation between the logarithm of conductivity and the reciprocal of temperature deviates from linearity at high temperatures ( T > θ D /2), θ D being the Debye temperature, due to the contribution of the variable-range hopping conduction. The results obtained are as follows: 1. (1) when X is less than 15, the electric behavior of the glass is similar to that of sodium phosphate glasses, which show the ionic conduction; 2. (2) when X is more than 15, the electric behavior of the glass is similar to that of iron phosphate glasses, which show electronic conduction; 3. (3) when X is 15, the transition of electric behavior depends upon the amount of Fe 2+ ions in the glass.

Journal ArticleDOI
TL;DR: In this paper, the electrical resistivity ρ and thermopower S of amorphous FexCo80−xB20 alloys in the temperature range 4 K
Abstract: A systematic study of the electrical resistivity ρ and thermopower S of amorphous FexCo80−xB20 alloys in the temperature range 4 K

Journal ArticleDOI
TL;DR: In this article, a quantum statistical theory of physisorption kinetics is formulated taking proper account of the surface phonon modes of a semi-infinite solid, and an effective surface Debye temperature is deduced that is about 0.65 to 0.8 times the bulk debye temperature.

Journal ArticleDOI
TL;DR: In this article, measurements of the low-temperature specific heat in different magnetic fields are presented for the metallic glass Cu0.46Zr0.54 in the as-quenched and fully relaxed states.
Abstract: Measurements of the low-temperature specific heat, in different magnetic fields, are presented for the metallic glass Cu0.46Zr0.54 in the as-quenched and fully relaxed states. The data are analysed in terms of the theory of type II superconductivity and the variations of the relevant parameters are discussed. Structural relaxation changes the electron density of states at the Fermi level, the Debye temperature and the average of the square of the electron-phonon matrix elements in the opposite direction to that of crystallisation. The most strongly affected quantity is the electron-phonon interaction. In the two different glassy states, fluctuation contributions to the specific heat are observed in the critical region which exhibit contrasting behaviour in an applied magnetic field just below the transition points. An explanation is suggested in terms of a partial suppression by the structural relaxation of structural defects of the type and size of those which have been identified recently in glassy metals by a computer simulation.

Journal ArticleDOI
TL;DR: In this article, an analytical expression for the X-ray Debye temperature (θM) of a hexagonal crystal in terms of the elastic constants was derived and used to calculate θM for hexagonal crystals of 41 elements and compounds.
Abstract: With the Debye continuum model an analytical expression is derived for the X-ray Debye temperature (θM) of a hexagonal crystal in terms of the elastic constants and this expression is used to calculate θM for hexagonal crystals of 41 elements and compounds. Calculated results by numerical integration are also presented for the X-ray Debye temperature perpendicular to the hexad axis, θ⊥, and that parallel to it, θ||. The calculated results are compared with experimental values, wherever data are available. A correction factor for the effect of dispersion is determined from the experimental data.

Journal ArticleDOI
TL;DR: In this article, the heat capacity of (Mo 0.60 Ru 0.40 ) 100−x B x metallic glasses has been measured in the temperature range 2-15 K for glasses with 14 ≤ × ≤ ≤ 22.

01 Jan 1982
TL;DR: In this paper, the heat capacities of synthetic single crystats of Mg2Sio4 (forsterite), Mn2SiOa (tephroite), and co2Siaa (cobalt olivine) were measured between 5 and 3g0 K using an adiabatically shielded calorimeter.
Abstract: The heat capacities of synthetic single crystats of Mg2Sio4 (forsterite), Mn2Sioa (tephroite), and co2Sioa (cobalt olivine), were measured between 5 and 3g0 K using an adiabatically shielded calorimeter. Mg2SiOa is diamagnetic, and its heat capacity follows a normal sigmoidal curve at low temperatures. co2sioa shows a single sharp )r-type transition at 49.85+0102 K associated with the antiferromagnetic ordering of the magnetic moments of the Co2+ ions into a collinear spin arrangement below 49.8 K. In contrast to co2sioa, Mn2Sioa has two transitions in ci, a sharp L-type transition at 47.3g10.05 K and a smaller "shoulder" in Ci centered near 12 K. The upper transition corresponds to the paramagnetic (disordered) to collinear antiferromagnetic ordering of the Mn2+ moments, whereas the shoulder near 12 K corresponds to the change from the collinear to a canted spin structure. Our calorimetric values for the antiferromagnetic-paramagnetic transition temperature (N6el Temperature) are in excellent agreement with those obtained by powder magnetic susceptibility measurements, 49t2 K and 5015 K for co2Sioa and Mn2Sioa respectively. The thermal Debye temperature, 0$, of Mg2Sioa calculated from our c$ measurements between 6.3 and 13.8 K is 768+15 K and agrees well with the elastic vaiue ofi of 758 K based on the mean sound velocity calculated from the room temperature elastic stiffness constants (ci:) of Graham and Barsch. At 298.15 K (25"c) the molar heat capacities are 118.6, 128.7 , and 133.4 J/(mol . K) and the molar entropies are 94.11-r0.10, 155.910.4 and, 142.6-+0.2 Jl(mol . K) respectively for Mg2SiO4, Mn2SiOa, and Co2SiOa.

Journal ArticleDOI
TL;DR: The crystal structure of the hollandite type phase Ba1.17Ti5.04Al2.10O16 has been determined by neutron diffraction powder methods in the temperature range 20 −1060°C as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a study of the cohesion and thermodynamic properties of fluorite-type AB2 crystals has been carried out by means of an interionic potential, which consists of the long-range Coulomb interactions and short-range overlap repulsion and van der Waals (vdW) dipole-dipole and dipole quadrurupole interactions.
Abstract: A study of the cohesion and thermodynamic properties of fluorite‐type AB2 crystals has been carried out by means of an interionic potential, which consists of the long‐range Coulomb interactions and short‐range overlap repulsion and van der Waals (vdW) dipole–dipole and dipole–quadrupole interactions. The vdW coefficients have been evaluated from the Slater–Kirkwood variational method. The effect of second‐neighbor overlap repulsion is incorporated via the Hafemeister and Flygare approach. The calculations of cohesive energy, Debye temperature, Gruneisen constant, thermal expansion coefficients, molecular force constant, reststrahl frequency, compressibility, and its pressure and temperature derivatives have been performed for ten solids. The agreement between theoretical and experimental results is generally good.