Showing papers on "Debye model published in 1981"
TL;DR: In this paper, the magnetic entropy of a typical 3-dimensional ferromagnetic substance near the Curie temperature as a function of temperature and magnetic field strength was calculated and compared with the experimental results.
250 citations
TL;DR: In this paper, the elastic moduli of fused quartz have been determined by ultrasonic measurements under high hydrostatic compressive stress and showed a nonlinear decrease to a minimum value at 2.1-2.5 GPa, and thereafter an increase with increasing pressure.
Abstract: The elastic moduli of fused quartz have been determined by ultrasonic measurements under high hydrostatic compressive stress and showed a nonlinear decrease to a minimum value at 2.1–2.5 GPa, and thereafter an increase with increasing pressure. Changes in the Debye temperature and the Gruneisen constant are determined using the present results. Assuming a contribution of the fourth‐order elastic constants to the nonlinear dependence, C1111, C1112, C1122, and C1123 have been tentatively evaluated to be 11.0±1.0, 10.8±3.6, 22.7±11.1, and 8.6±2.0 TPa, respectively. However, the possibilities of a complicated potential curve or a higher‐order phase transition are also discussed.
162 citations
TL;DR: In this paper, the authors presented transport and Raman data for samples of Ti1+xS2 with carrier densities, determined from the Hall coefficient, ranging from approximately 1020 cm-3 to approximately 3*1021 cm3.
Abstract: Transport and Raman data are presented for samples of Ti1+xS2 with carrier densities, determined from the Hall coefficient, ranging from approximately 1020 cm-3 to approximately 3*1021 cm-3. No dependence on carrier concentration, n, is observed for the frequency of the A1g Raman-active phonon, whereas a strong variation is seen in the non-linear temperature dependence of resistivity, rho (T), between 4.2K and 290K. Fitting the resistivity to a power law, rho (T)- rho (o) varies as Tp, in the range 110K to 290K, the authors find p=2.3 for n approximately 1020 cm-3 and p=1.6 for n approximately *1021 cm-3. For samples with carrier concentrations above approximately 7*1020 cm-3 a stronger temperature dependence is observed below 100K. The temperature-dependent part of the resistivity is proportional to n-0.74 at room temperature and n-0.60 at 150K. It is argued that the scattering mechanism in TiS2 is with both optical and acoustic phonons. Below the Debye temperature the form and variation with carrier concentration of the temperature dependence may be described by a model involving both intra- and inter-valley scattering by acoustic phonons.
100 citations
TL;DR: In this article, the present status of theoretical and experimental investigations of fine metallic particles (FMPs) with characteristic dimension from 100 to 1 nm is considered, and an analysis is made of the influence of the size of FMP on the structure, on the phonon spectra, the heat capacity, the Debye temperature, the behavior of the FMP in an electromagnetic field, the relaxation of the electronic spins, the magnetic susceptibility, and the optical properties.
Abstract: This review considers the present status of theoretical and experimental investigations of fine metallic particles (FMP) with characteristic dimension from 100 to 1 nm. An analysis is made of the influence of the size of FMP on the structure, on the phonon spectra, the heat capacity, the Debye temperature, the behavior of the FMP in an electromagnetic field, the relaxation of the electronic spins, the magnetic susceptibility, and the optical properties. Changes in the structure and in the phonon spectrum are due chiefly to disintegration of the surface layers of atoms and to the large curvature of the surface of the FMP. The electronic states of FMP are treated with allowance for the pronounced discreteness of the levels. A comparison is made of theoretical and experimental results on the effect of the parity of the number of electrons in the particles on the paramagnetic susceptibility and on the Knight shift. Relaxation of electron spins in FMP of alkali metals is discussed with allowance for the effect of the surface and of impurities, and also of a possible contribution from the pronounced discreteness of phonon and electron states. Investigations of optical properties and of plasma oscillations indicate an important role of surface states in relation to electronic transitions in FMP.
61 citations
TL;DR: In this article, the authors measured the thermal expansion of single-crystal fayalite at temperatures between 25 °C and 850 °C. The results show the presence of anomalous expansion in the b axis, which is correlated to the anomalous variation of elastic moduli with temperature.
Abstract: Thermal expansion of single-crystal fayalite has been measured by a dilatometric method at temperatures between 25 °C and 850 °C. The results show the presence of anomalous expansion in the b axis, which is correlated to the anomalous variation of elastic moduli with temperature. Gruneisen's parameter is 1.10 and the thermal Debye temperature is 565 K, which is close to the acoustic Debye temperature of 511 K.
59 citations
TL;DR: In this paper, the effect of adsorbed gases on the interplanar spacing between the outermost Pt layers of the Pt(100)−(1 × 1) surface at 175 K was studied.
45 citations
TL;DR: In this article, the elastic constants of polycrystalline copper were determined between 4 and 295 K by measuring ultrasonic velocities, longitudinal and transverse, and the Hershey-Kroner-Eshelby theory agreed best with observation.
Abstract: Elastic constants of polycrystalline copper are determined between 4 and 295 K by measuring ultrasonic velocities, longitudinal and transverse. Five elastic constants are given: longitudinal modulus, shear modulus, Young's modulus, bulk modulus (reciprocal compressibility), and Poisson's ratio. Considering eight theories of single-crystal :polycrystal elastic constants, the Hershey-Kroner-Eshelby theory agrees best with observation, within 1% for the shear modulus, G. (Voigt and Reuss first-order bounds on (G differ by 29%.) A problem exists concerning the calculation of the Debye temperature of polycrystalline aggregates.
43 citations
01 Jan 1981
TL;DR: In this paper, the experimental situation of amorphous solids is reviewed and it is not altogether clear what fraction, if any, of the specific heat anomaly is truly intrinsic, independent of the prior history of the sample and of the presence of trace impurities.
Abstract: One of the puzzles presented by amorphous solids is that their low-temperature specific heat exceeds that predicted on the basis of the Debye theory by a considerable amount. This phenomenon appears to be sufficiently general to be considered a characteristic one. However, it is not altogether clear what fraction, if any, of the specific heat anomaly is truly intrinsic, i.e., independent of the prior history of the sample and of the presence of trace impurities. In this chapter we will review the experimental situation.
42 citations
TL;DR: In this article, the local density of states (LDS) of individual atoms at the boundaries was computed by the recursion method, and the thermodynamic quantities were calculated from the LDS's.
41 citations
TL;DR: In this article, the selective sensitivity of the calculated polarization profiles to the surface relaxation δ 12 and to various non-structural model features was investigated, and the geometry of Pt(111) was established as unreconstructed with a possible slight outward relaxation of the topmost atomic layer (δ 12 = 0.5% ± 1.0% of the bulk interlayer distance).
38 citations
TL;DR: In this article, measurements have been made of the pressure and temperature dependences of the velocities of longitudinal and transverse ultrasonic waves in a glass having the composition 0.58ZrF 4 : 0.08ThF 4.
TL;DR: In this article, the authors measured the heat capacities of SnSe and SnSe2 in the temperature range 230-580 K using a computer interfaced differential scanning calorimeter.
TL;DR: In this article, the electronic specific heat coefficient gamma, Debye temperature ThetaD and spin-wave stiffness constant D are determined for amorphous Fe1-xBx alloys over the temperature range 1.5-6K.
Abstract: The low-temperature specific heats of amorphous Fe1-xBx alloys (x = 0.14, 0.16, 0.18 and 0.20) have been measured over the temperature range 1.5-6K. The results are well represented by the equation C = gammaT + alphaT3 + sigmaT3/2 and the electronic specific heat coefficient gamma , Debye temperature ThetaD and spin-wave stiffness constant D are determined. Both gamma and ThetaD values are found to decrease rapidly with increasing B concentration. The largest gamma value is twice as large as that for the pure BCC Fe. The value of ThetaD is also very high, compared with the other metal-metalloid amorphous alloys. Such high values are attributed to the existence of the covalent bond between Fe and B atoms. The present results are also discussed from the point of view of Invar characteristics particularly in comparison with a typical Invar Fe0.65Ni0.35 alloy. The large gamma and low D values are observed in both alloy systems, while the high ThetaD in amorphous Fe-B alloys is in sharp contrast with the lattice softening phenomena in Fe-Ni alloy, which is believed to be one of the characteristic features of an Invar alloy.
TL;DR: The low-temperature specific heat of an amorphous Mg0.7Zn0.3 alloy and of the same alloy subjected to heat treatment are measured over the temperature range 1.6-4.2K as mentioned in this paper.
Abstract: The low-temperature specific heats of an amorphous Mg0.7Zn0.3 alloy and of the same alloy subjected to heat treatment are measured over the temperature range 1.6-4.2K. All the results fit well to the simple equation C= gamma T+ alpha T3. The electronic specific heat coefficient gamma for the amorphous phase is found to be very close to the free-electron value on the assumption that both Mg and Zn donate two conduction electrons per atom. The lattice specific heat is well described by the Debye model in sharp contrast with the metal-metalloid glasses, where the departure from the T3 dependence is appreciable. This is attributed to the difference in the packing fraction of atoms between the metal-metal and metal-metalloid glasses. The electrical resistivity is also measured over the temperature range 4.2-300K. The reliable determination of 2kF/Kp allowed discussion of the observed negative TCR in relation to the extended Ziman theory.
TL;DR: In this paper, low temperature specific heat measurements on the second stage graphite intercalation compounds KHgC8 and RbHgC 8 showed anomalies characteristic of superconductivity at 1.93 K and 1.46 K respectively.
TL;DR: In this paper, internal friction, ultrasonic attenuation, and electric modulus measurements on alumina, which are inconsistent with simple Debye theory, are found to be in good agreement with each other when analyzed with use of the "universal" dielectric response theory.
Abstract: Internal friction, ultrasonic attenuation, and electric modulus measurements on $\ensuremath{\beta}$- alumina, which are inconsistent with simple Debye theory, are found to be in good agreement with each other when analyzed with use of the "universal" dielectric response theory. It is suggested that this theory may be used to analyze mechanical relaxation data from other ionic conductors.
TL;DR: In this article, the specific heat Cv of the ternary semiconducting compounds ZnSiP2, CdGeAs2 and CdNiP2 was determined experimentally in a temperature region within 2 and 30 K.
Abstract: The specific heat Cv of the ternary semiconducting compounds ZnSiP2, ZnSiAs2, ZnSnAs2, and CdGeAs2 is determined experimentally in a temperature region within 2 and 30 K. From the results the Debye temperatures, frequency moments, and standard entropies are calculated. By dividing Cv into a Debye and an Einstein contribution the approximate shape of the low frequency phonon mode is estimated.
TL;DR: In this paper, the temperature dependence of dc conductivity of V2O5, layers ≈ 500 nm thick, was studied from room temperature down to 28 K. The following vaiues were deduced: activation energy for hopping, WH ≈ 0.09 eV, Anderson disorder energy, WD = 0.13 eV and the Debye temperature, θD ≈ 325 K.
Abstract: The temperature dependence of the dc conductivity of V2O5, layers ≈ 500 nm thick is studied from room temperature down to 28 K. The following vaiues are deduced: activation energy for hopping, WH ≈ 0.09 eV, Anderson disorder energy, WD = 0.13 eV, and the Debye temperature, θD ≈ 325 K.
Nous avons etudie la variation de la conductivite de films de V2O5, (epaisseur 500 nm) entre 300 et 28 K. A partir de ces mesures nous deduisons les valeurs suivantes: energie de saut WH ≈ 0.09 eV, energie de desordre d'Anderson WD = 0,13 eV et temperature de Debye θD ≈ 325 K.
TL;DR: In this article, a LEED analysis of a clean Mo(110) surface was performed at room temperature and a detailed examination was made of the influence of non-structural parameters including the surface Debye temperature, the correlation-exchange contribution to the ion-core scattering potential and energy dependence of the effective inner potential.
Abstract: A LEED analysis of a clean Mo(110) surface was performed at room temperature. A detailed examination was made of the influence of non-structural parameters including the surface Debye temperature, the correlation-exchange contribution to the ion-core scattering potential and energy dependence of the effective inner potential. Comparison of experimental and theoretical results was made quantitatively and, after optimisation of the relevant theoretical parameters, a value for the surface interlayer spacing of 2.19+or-0.04 AA was obtained; this represents a contraction of about 1.6+or-2% from the bulk interlayer spacing.
TL;DR: In this paper, the effect of phonon fluctuations on defect transfer-integrals is explicitly taken into account, in particular the rate of incoherent defect transitions up to second order in J and the temperature dependence of the multi-phonon processes is discussed in the regime above half of the Debye temperature.
Abstract: For light interstitials in deformable host-materials (“small-polaron”-like systems) the theory of multi-phonon transitions is developed beyond the so-called Condon approximation, i.e., the effect of phonon fluctuations on the defect transfer-integrals J is explicitly taken into account. In particular the rate of incoherent defect transitions is evaluated up to second order in J and the temperature dependence of the multi-phonon processes is discussed in the regime above half of the Debye temperature.
Fur leichte Zwischengitterteilchen in deformierbaren Wirtsmaterialien (Systeme vom Typ des kleinen Polarons) wird die Theorie der Viel-Phononen-Ubergange jenseits der sogenannten Condon-Naherung entwickelt, d. h., die Auswirkungen der Fluktuationen des Phononensystems auf die Ubergangs-Integrale J des Defekts werden explizit berucksichtigt. Insbesondere wird die Rate der inkoharenten Ubergange in zweiter Ordnung in J bestimmt und die Temperaturabhangigkeit der Viel-Phononen-Prozesse im Bereich oberhalb der halben Debye-Temperatur diskutiert.
TL;DR: In this paper, the experimental heat capacity data for the Laves phase R Fe 2 intermetallic compounds (R =Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been determined over the temperature range 8 to 300 K. The error in these data is thought to be less than 1%.
TL;DR: In this paper, the Debye temperature determined from the temperature dependence of the recoilless fraction for the gas-evaporated iron particles having average diameter of 66 A does not differ from the bulk value.
TL;DR: In this article, the electrical conductivity of iron-containing silica glasses was measured from 80 to 350 K. The conductivity data were analyzed based on the hopping conduction theory and the hopping binding energy (Wp) and disorder energy WD were calculated from the activation energy at high and low temperatures.
Abstract: The electrical conductivity of iron-containing silica glasses was measured from 80 to 350 K. The conductivity data were analyzed based on the hopping conduction theory. The hopping binding energy (Wp) and disorder energy WD) were calculated from the activation energy at high and low temperatures. The disorder energy obtained was much lower than reported for FeO-P2O5 glasses, but similar to that for vandium-containing glasses.
TL;DR: The Tian-Calvet microcalorimetric method has been applied to the determination at 1323 K of ΔH ( O 2 ), the partial molar enthalpy of mixing of oxygen in vanadium, niobium and tantalum as discussed by the authors.
TL;DR: In this article, the systematics of hyperfine interactions for 57 Fe in matrices of α-C, Si, Ge and α-Sn indicate strong atomic volume effects, attributed to a very large compression of Fe atoms in the diamond matrix.
TL;DR: In this paper, the low temperature heat capacities of 13 group IV chalcogenides were examined and it was shown that the heat capacity of groups with largely isotropic structure (GeTe, SnSe, GeSe, SnTe, GeS2 and SnS2) can be represented by pairs of two-dimensional Debye functions for the longitudinal and transverse lattice vibrations.
Abstract: The low temperature heat capacities of 13 group IV chalcogenides are examined. The heat capacity of crystals with largely isotropic structure (GeTe, SnSe, SnTe, PbS, PbSe, PbTe) can be represented within ±3% by a three-dimensional Debye function (θ3=205, 230, 175, 225, 150 and 130, respectively). The heat capacity of crystals with anisotropic structures (GeS, GeSe, SnS, GeS2 and SnS2) could only be represented by pairs of two-dimensional Debye functions for the longitudinal and transverse lattice vibrations (error ±0.5 to 3%;θ2(l)=505, 345, 400, 705, 480 and 570, respectively, andθ2(t)=200, 185, 160, 175, 100 and 265, respectively).
TL;DR: The specific heat of neutron-irradiated Nb/sub 3/Al has been measured in the temperature range 1.3-25 K for fluences of 1.5-1.3 x 10/sup 18/n/cm/sup 2/ (E>1 MeV).
Abstract: The specific heat of neutron-irradiated Nb/sub 3/Al has been measured in the temperature range 1.3--25 K for fluences of 1.3 x 10/sup 18/ and 1.3 x 10/sup 19/ n/cm/sup 2/ (E>1 MeV). A reduction in the superconducting transition temperature is accompanied by an increase in transition width with increasing fluence. The Debye temperature increases 20%, and the electronic density of states shows a slight decrease that is within error limits, relative to the unirradiated material.
TL;DR: In this paper, a quasiharmonic approximation of the thermal vibration of atoms is used to measure the intensity of Bragg reflexions from powder samples TaC0.99 and TaC 0.81 in the temperature range from 22 to 940 °C.
Abstract: Intensities of Bragg reflexions from powder samples TaC0.99 and TaC0.81 are measured in the temperature range from 22 to 940 °C. The values of Debye temperature ΘM corresponding to 22 °C are (475 ± 4) and (440 ± 3) K, for the two respective compositions, indicating thus the decrease of ΘM with increasing deficiency of carbon atoms in the structure. The measured temperature dependence of ΘM can be described by a quasiharmonic approximation of the thermal vibration of atoms. The electron distributions of the atoms are analysed in terms of deviations of the measured scattering factors from the theoretical ones, calculated for the free atoms in the directions [hhh], [hho], and [h00]. It is found that, in comparison with the free-atom model, the charge density of tantalum atom is extended radially and the carbon atom is contracted.
TL;DR: In this paper, the six independent elastic constants of single crystals of tetragonal MgF2 have been measured over the temperature range 4.2-300 K. The data indicate a high degree of anisotropy in the atomic force interactions.
Abstract: The six independent elastic constants of single crystals of tetragonal MgF2 have been measured over the temperature range 4.2–300 K. All six of the conventional constants show normal negative temperature dependences. The shear constants associated with normal modes of deformation tend to be weak, and one of these, (1)/(2) (C11−C12), also exhibits a weak positive temperature dependence as do all other fluorides with the rutile structure for which data are available. The data indicate a high degree of anisotropy in the atomic force interactions. A Debye temperature evaluated from the single‐crystal elastic constants when combined with two empirical Einstein temperatures satisfactorily describes tabulated heat‐capacity data to within 1%.
TL;DR: In this article, the application of the Lindemann rule to the estimation of the Debye temperature of diamond-like semiconducting compounds is discussed, and the classical formula of LINDEMANN was modified by a constant K2: θ = K1 + K2.
Abstract: Application of the Lindemann rule to the estimation of the Debye temperature θ of diamond like semiconducting compounds is discussed. The classical formula of LINDEMANN was modified by a constant K2: θ = K1 + K2. The constants K1 and K2 are given for AIIIBV, AIIBVI, AIIBIVC2V and AIBIIIC2VI compounds. These were calculated as well from X-ray diffraction data as from θ evaluated from specific heat capacity and elastic constants.
Es wird die Anwendung der Lindemann-Regel zur Abschatzung von Debye-Temperaturen θ fur diamantartige halbleitende Verbindungen diskutiert. Die klassische LINDEMANN-Formel wird durch eine Konstante K2 erweitert: θ = K1 + K2. Die Konstanten K1 und K2 sind fur AIIIBV-, AIIBVI-, AIIBIVC2V- und AIBIIIC2VI-Verbindungen angegeben. Ihre Berechnung erfolgt sowohl aus Rontgenbeugungsdaten als auch aus θ-Werten, die sich aus der spezifischen Warmekapazitat und elastischen Konstanten herleiten.