Showing papers on "Debye model published in 1988"
TL;DR: In this article, the electrical resistivity, thermal conductivity, and specific heat of a series of high-temperature superconducting compounds of the form RBa/sub 2/Cu/sub 3/O/sub 7/, with R = Y, Eu, Gd, Dy, and Er.
Abstract: We have measured the electrical resistivity, thermal conductivity, and specific heat of a series of high-temperature superconducting compounds of the form RBa/sub 2/Cu/sub 3/O/sub 7/, with R = Y, Eu, Gd, Dy, and Er. Our results show that the afore-mentioned physical properties are virtually identical for all samples considered. In particular, the molar specific heats are identical to within +- 2% and exhibit Debye-type behavior. We observe a nearly constant thermal conductivity above T/sub c/, but a rather sudden increase developes as the temperature is lowered below the critical temperature. The electrical resistivity is nearly linear in the normal state. Thermal and electrical conductivities indicate that for T>T/sub c/, the predominant electron scattering mechanism is due to phonon interactions. Using electrical resistivity data and the Wiedemann-Franz law, we estimate the magnitude of the electronic component of the thermal conductivity to be an order of magnitude smaller than the measured thermal conductivity. We thus conclude that heat transport is predominantly by phonons. The enhancement of the lattice conduction below the critical temperature is understood as a reduction of carrier-phonon scattering as electrons condense into Cooper pairs. This lends support to standard Bardeen-Cooper-Schrieffer-type superconductivity. An estimate of the superconducting transition temperatures ismore » made using the electron-phonon coupling constants and Debye temperatures deduced from the data which brackets the observed T/sub c/ quite well. We discuss the thermal conductivity at very low temperature in terms of a phonon mean-free path limited by pores in the samples.« less
69 citations
TL;DR: In this paper, the phonon spectrum in YBa/sub 2/Cu/sub 3/O/sub 7/ was calculated in the orthorhombic structure using an unscreened rigid-ion model as a first approximation.
Abstract: The phonon spectrum in YBa/sub 2/Cu/sub 3/O/sub 7/ is calculated in the orthorhombic structure using an unscreened rigid-ion model as a first approximation. The calculated values of the ''neutron-weighted'' phonon density of states, the optical frequencies, the Debye temperature, and the mean-squared vibrational amplitudes are in fair agreement with the values reported from various experiments.
67 citations
TL;DR: In this article, the authors measured the low-temperature thermal conductivity and specific heat of amorphous solids and concluded that the thermal properties do not depend on the coordination number.
Abstract: We have measured the low-temperature thermal conductivity and specific heat of ${\mathrm{CdGeAs}}_{2}$ to investigate the influence of coordination number on the thermal properties of amorphous solids. ${\mathrm{CdGeAs}}_{2}$ is tetrahedrally bonded in the crystalline state and strong evidence exists that this local order is preserved in the amorphous state. The thermal conductivity of the amorphous material was measured from 0.1 to 300 K. It displays the same behavior as all other glasses: a ${T}^{2}$ dependence below 1 K, a wide range of temperature over which the conductivity is approximately temperature independent, and a thermal conductivity at high temperatures that approaches the minimum thermal conductivity as described by Slack. The specific heats of c-${\mathrm{CdGeAs}}_{2}$ and a-${\mathrm{CdGeAs}}_{2}$ were measured from 0.1 to 50 K. Below 1 K, the amorphous material shows the excess specific heat that is characteristic of amorphous solids. Above 1 K, the specific heat of the amorphous material, when compared to the Debye model, closely resembles the specific heat of the crystal. We have also measured the thermal conductivity of a sputtered film of a-Ge from 30 to 300 K and compare our results to previous measurements of the thermal properties of a-Si and a-Ge. On the basis of our experimental findings, we conclude that the thermal properties of amorphous solids do not depend on the coordination number.
40 citations
TL;DR: In this paper, Neutron inelastic scattering measurements were carried out on semicrystalline and highly crystalline polyethylenes with degrees of crystallinity of 0.46 and 0.96, respectively, at 10 K to investigate low-energy excitations below 10 meV.
38 citations
01 Jul 1988-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, a relationship between Tc and the Debye temperature, Θ, is proposed based on reported experimental data, and experiments are suggested to shed more light on the relationship.
Abstract: Ion bombardment of samples composed of unlike atoms have been reported by numerous authors to lead to spatial redistribution of atoms, i.e., ion-beam mixing. A critical temperature, Tc was found experimentally for several systems. It marks the change in the dominant mixing mechanism. Here, a relationship between Tc and the Debye temperature, Θ, is proposed based on reported experimental data. Experiments are suggested to shed more light on the relationship.
37 citations
TL;DR: Ion-channeling measurements reveal that the thermal vibrational amplitude, u/sub 1/, decreases markedly as the temperature of orthorhombic single crystals of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ is lowered from 300 to 220 K.
Abstract: Ion-channeling measurements reveal that the thermal vibrational amplitude, ${u}_{1}$, decreases markedly from 0.008 to 0.0056 nm as the temperature of orthorhombic single crystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ is lowered from 300 to 220 K. The rate of this decrease slows at lower temperatures, with ${u}_{1}$ reaching a value of 0.0042 nm at 100 K. Further cooling of the sample across the superconducting transition region (to 85 K) produces an abrupt, additional decrease in ${u}_{1}$ to 0.0035 nm. This abrupt lattice stiffening corresponds to an \ensuremath{\sim}140 K increase in Debye temperature across the superconducting transition.
33 citations
TL;DR: In this article, the temperature dependence of the isomer shift S and recoil-free fraction ƒ of the 21.6 keV Mossbauer resonance of 151Eu is studied in the high-Tc superconductor EuBa2Cu3O7−x between 4.2 and 300 K.
33 citations
TL;DR: These data indicate that the authors achieve complete suppression of the heavy-fermion ground state in CeCu/sub 6/ with this high applied magnetic field, in sharp contrast with results on uranium systems, indicating a fundamental difference in theheavy-fer molybdenum ground state.
Abstract: Measurement of the specific heat of CeCu/sub 6/ in fields to 24 T between 1.8 and 8 K and of the magnetization in fields to 20 T at 1.3 and 4.2 K is reported. The value of ..gamma.. ( = CT) in 24 T is 350 mJmol K/sup 2/. The slope of the CT-vs-T/sup 2/ data, proportional to the Debye temperature, in 24 T is the same as that for LaCu/sub 6/ in zero field, with no low-temperature upturn in the CT data in 24 T observed. These data indicate that we achieve complete suppression of the heavy-fermion ground state in CeCu/sub 6/ with this high applied magnetic field. These results are in sharp contrast with results on uranium systems, indicating a fundamental difference in the heavy-fermion ground state. Implications for de Haas-van Alphen experiments are discussed
32 citations
TL;DR: The feasibility of sintered gadolinium gallium garnet (GGG) as refrigerant for magnetic refrigerators has been investigated by measurement of its specific heat and magnetisation.
Abstract: The feasibility of sintered gadolinium gallium garnet (GGG) as refrigerant for magnetic refrigerators has been investigated by measurement of its specific heat and magnetisation. The heat capacities of sintered samples with different densities were determined between 2 K and 300 K and below 40 K in applied magnetic fields up to B=6 T. The specific heat was found to be within 5% identical to that of monocrystalline GGG; the density of the sintered specimen is only of minor influence upon the heat capacity. The magnetic moments were measured at magnetic fields of 0.1, 1.0, 2.5, and 4.0 T in the temperature range from 4 to 30 K. The authors present a phenomenological model for the splitting of the energy levels in GGG. This model enables them to describe the specific heat of GGG accurately for T>4 K in the various applied magnetic fields, to calculate the temperature and magnetic field dependence of the magnetisation and to explain the magnetic susceptibility. They separated the lattice contribution and the magnetic contribution of the specific heat, and derived the Debye temperature as a function of temperature. Thus, they provide a numerical method to calculate the magnetic entropy. They found that the same entropy-diagram S(T,B) can be used for both sintered and monocrystalline GGG. The thermodynamic standard functions (in zero magnetic field) have been calculated.
32 citations
TL;DR: In this article, the elastic properties of lead phosphomolybdate glasses were investigated using ultrasonic velocity measurements at 10MHz, and the composition dependence of elastic moduli, Poisson's ratio and the Debye temperature were found consistent with a structural model proposed earlier.
30 citations
TL;DR: In this article, the role of phonons in the superconducting phase transition has been investigated using infrared reflectivity and inelastic neutron scattering experiments on single phase YBa2Cu3O7−δ(δ≊0.1,T c =94 K, ΔT 10−90=1 K).
Abstract: In order to obtain insight into the role played by the phonons in the superconducting phase transition, we have performed infrared reflectivity and inelastic neutron scattering experiments on single phase YBa2Cu3O7−δ(δ≊0.1,T
c
=94 K, ΔT
10–90=1 K). These experimental results, together with published Raman scattering and specific heat data are used to determine the parameters of a rigid-ion model; the model is able to reproduce qualitatively the experimental data. On the basis of our model we derive and discuss the phonon density of states and the pattern of atomic displacements of some important vibrational modes. In particular, the model reveals the existence of high-frequency oxygen breathing modes and of low-frequency copper dimerization modes in both the CuO3-chains and the CuO2-planes. Furthermore, Jahn-Teller like oxygen modes exist in the chains. The possible role of these modes with respect to the pairing mechanism is discussed. In addition there exist low-frequency “chain-degrading” modes which favour jumps of oxygen atoms out of the CuO3-chains into neighbouring vacant sites in the basal plane.
TL;DR: In this article, the equation of state and the electronic band structure of solid LiH have been calculated using the local density functional theory with Ceperley and Alder's exchange-correlation potential in the muffin-tin approximation.
TL;DR: In this article, the specific heat, C p has been measured in the range of 0.4 to 20 K and the electrical resistance, B c 2 (0), for the Bi 2,1 Sr 2 CaCu 2 O 8+x, specimen is estimated to be 19 T.
Abstract: The specific heat, C p has been measured in the range of 0.4 to 20 K and the electrical resistance in the range 20 to 120 K in magnetic fields up to 7 T of Bi 2.1 Sr 2 CaCu 2 O 8+ x . Below 4 K the effects of lattice dispersion are more pronounced than in YBa 2 Cu 3 O 7 , there is an upturn in C p T , and evidence for the presence of a T -term ( γ = 4 ± mJ/mol. K 2 ). A value for the Debye temperature of 260 ± 6 K is obtained. The upper magnetic critical field, B c 2 (0), for the Bi 2,1 Sr 2 CaCu 2 O 8+x , specimen is estimated to be 19 T.
TL;DR: The shift caused by charge transfer shows a ${T}^{4}$ dependence at low temperatures, in agreement with theoretical calculations.
Abstract: Using the high-resolution 93.3-keV transition in $^{67}\mathrm{Zn}$ we studied the temperature dependence of the Lamb-M\"ossbauer factor (LMF), the center shift, and the quadrupole interaction in ZnO single crystals. The temperature range for this high-energy M\"ossbauer resonance could be extended up to liquid-nitrogen temperature (77.3 K). The mean-square atomic displacements show very little anisotropy. The results on the LMF can well be described by the Debye model with ${\mathrm{FTHETA}}_{D}^{\mathrm{LMF}\mathrm{\ensuremath{\sim}}317}$ K. The quadrupole interaction is ${e}^{2}$qQ/h=2.401\ifmmode\pm\else\textpm\fi{}0.004 MHz at 4.2 K and it is independent of temperature within 1%. At 77.3 K the center shift has changed by 9.0 \ensuremath{\mu}m/s compared to its value at 4.2 K. Already at low temperatures, phonon-induced electron transfer from zinc to oxygen is observed. The shift caused by charge transfer shows a ${T}^{4}$ dependence at low temperatures, in agreement with theoretical calculations.
TL;DR: The low-temperature specific heat has been measured on both orthorhombic and tetragonal single crystals of YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub delta/.
Abstract: The low-temperature specific heat has been measured on both orthorhombic (superconducting) and tetragonal single crystals of YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub delta/. The Debye temperature extracted from the T/sup 3/ term decreases with increasing oxygen vacancy concentration consistent with glassy behavior in disordered solids. A linear ..gamma..T term, however, exists for both phases. It is proposed that this term is at least in part electronic, even in the superconducting state, and is due to extended or localized states at the Fermi energy
TL;DR: In this article, the Debye temperature theta D in Ni-Ti is discussed in relation to the crystallisation temperature Tx and also the characteristic temperature Delta involved in an expression for the temperature dependence of the electrical resistivity.
Abstract: The authors have measured the low-temperature specific heats in the range 1.5-6 K, the magnetic susceptibilities in the range 77-300 K and the electrical resistivities in the range 2-300 K for four Ni100-xTix (x=40, 55, 65 and 70) metallic glasses. The density of states near the Fermi level is found to be an increasing function of Ti concentration. A detailed comparison has been made on the electronic structure among the four similar metallic glasses Cu-Zr, Cu-Ti, Ni-Zr and Ni-Ti. The Debye temperature theta D in Ni-Ti is found to be the highest among these four systems. The Debye temperature theta D is discussed in relation to the crystallisation temperature Tx and also the characteristic temperature Delta involved in an expression for the temperature dependence of the electrical resistivity.
TL;DR: In this paper, the mean kinetic energy of O, Cu and other atoms in these materials was determined, and the Debye temperatures of Cu atoms in La2CuO4 and YBa2Cu3O7 were estimated to be extremely large, about 1500 and 2000 K, respectively.
TL;DR: In this article, the temperature dependence of the g-values arises from the dynamical interaction between the paramagnetic electrons and the phonons, and the Debye temperature is found as a function of temperature in all the four systems.
Abstract: Electron paramagnetic resonance of ZnSiF$\_6\cdot$ 6H$\_2$O:Ni$^{2+}$, ZnSiF$\_6\cdot$6D$\_2$O:Ni$^{2+}$, ZnSiF$\_6\cdot$6H$\_2$O:Mn$^{2+}$ and ZnSiF$\_6\cdot$6D$\_2$O:Mn$^{2+}$ lattices has been studied. From the temperature dependence of the zero-field splitting, the Debye temperature is found as a function of temperature in all the four systems. We find that the temperature dependence of the g-values arises from the dynamical interaction between the paramagnetic electrons and the phonons. The Debye temperature found from the zero-field splitting agrees with that found from the g-value. We have thus studied the interaction of paramagnetic electrons with lattice vibrations by a new method.
TL;DR: The elastic constants of PdH-x have been determined from ultrasonic velocity measurements for x up to 0.76 over the temperature range 4\char21{}300 K and the results are in good agreement with earlier measurements.
Abstract: The elastic constants of \ensuremath{\alpha}'-phase ${\mathrm{PdH}}_{\mathrm{x}}$ have been determined from ultrasonic velocity measurements for x up to 0.76 over the temperature range 4\char21{}300 K. For pure Pd and ${\mathrm{PdH}}_{0.67}$ the results are in good agreement with earlier measurements. The ${\mathrm{PdH}}_{0.76}$ data are for a higher hydrogen concentration than has previously been reported. The low-temperature concentration dependences of the Debye temperature and bulk modulus are given.
TL;DR: The Debye-Waller factor for a polyatomic crystal is derived in the Debye approximation in this article, where the acoustic phonon modes and optic modes are described with an Einstein model.
Abstract: The Debye-Waller factor for a polyatomic crystal is derived in the Debye approximation. If the crystal has a basis of p atoms per lattice point, it is shown that the specific-heat Debye temperature, ΘD, and the X-ray Debye temperature, ΘM, are related by ΘD ≃ ΘMP1/2 in the classical limit. The Debye and Einstein theories are then combined to yield an expression for the Debye-Waller factor of a polyatomic solid. The acoustic phonon modes are described with a Debye approximation, and the optic modes with an Einstein model. For temperatures above the Debye temperature, the Debye and Einstein parts of the Debye-Waller factor have the same dependence on temperature and diffraction vector. Thus, the two parts cannot be distinguished.
TL;DR: In this article, low temperature specific heat of disordered (fcc and fct) and ordered (CuAu I and Cu 3 Au types) FePd alloys has been measured.
Abstract: Low temperature specific heat of disordered (fcc and fct) and ordered (CuAu I and Cu 3 Au types) FePd alloys has been measured. The coefficients of electronic, phonon and magnon parts were analysed. The density of states attains a maximum, while the Debye temperature and the spin wave stiffness constant show a minimum at the boundary between the fcc and fct phases (33.4% Pd). For the ordered FePd and FePd 3 , a lower value of the density of states, and higher values of the Debye temperature and the spin wave stiffness are found. The spin wave stiffness constant for the 32% Pd alloy is also obtained by a thermomagnetic measurement. The ordered FePd gives a value of 93±10 meV A 2 , while FePd 3 110±10 meV A 2 at T = 0. Results are discussed from the standpoints of the itinerant electron ferromagnetism.
TL;DR: The role of various impurity phases, including BaCuO 2, is discussed in this article, where the intrinsic T -term was discussed in terms of the resonating-valence-bond model and tunnelling due to two-level systems.
Abstract: The heat capacity of a number of YBa 2 Cu 3 O 7 samples has been measured in the range 0.4 to 20 K to investigate the effect of paramagnetic chemical and phase impurities. Values for the T -term and Debye temperature are in the range 5.63–11.5 mJ/mol K 2 and 413–439 K, respectively. The role of various impurity phases, including BaCuO 2 , is discussed. The removal of the labile oxygen from YBa 2 Cu 3 O 7 to form the non-superconducting YBa 2 Cu 3 O 6 has enabled the determination of a value of ∼1.5 mJ/mol K 2 for the coefficient of the T -term that is intrinsic to the superconducting state. The intrinsic T -term is discussed in terms of the resonating-valence-bond- model and tunnelling due to two-level-systems.
TL;DR: In this article, the surface crystallography of arsenic covered Si(001) has been analyzed by low-energy neutral impact collision ion scattering spectroscopy (NICISS), and the 170° backscattered He neutrals and ions have been detected by a time-of-flight technique.
Abstract: The surface crystallography of arsenic covered Si(001) has been analyzed by low‐energy neutral impact collision ion scattering spectroscopy (NICISS). The 170° backscattered He neutrals and ions have been detected by a time‐of‐flight technique. The measured data show two well‐time‐resolved lines for He scattered at Si and As atoms, respectively. Hence NICISS angular pattern for Si and As could be measured simultaneously. Adsorption of arsenic lifts the original 1×2 reconstruction of the Si(001) substrate and forms itself a 1×2 As overlayer. The As overlayer is well described by a dimer arrangement with an interatomic distance of 2.55 A of the As dimers. From the ion scattering experiment considerable thermal vibrations of the As atoms in the overlayer have been concluded. Best agreement with Monte Carlo trajectory calculations is obtained for a Debye temperature of 120 K.
TL;DR: In this article, a statistical model was developed with the assumption that radioactive tracers migrate through interstitial channels represented by a periodic potential energy with barrier height ϵ, and the diffusion coefficient for a cubic crystal was given by D = 1 3 vlq ∗ exp (− ϵ k B T ), where v and l are, respectively, the mean migration speed and mean straight path.
TL;DR: In this article, specific heat measurements in ferroelectric single crystals for x = 0 and 0.02 were reported, from 2 -80 K. The data were accounted for with just the Debye model, and the possibility of an extra low-temperature term (C}_{\mathrm{LT}}$ and an extra high-tem temperature term (E}$) was added to account for extra oscillators.
Abstract: We report specific-heat measurements in ferroelectric (${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ba}}_{\mathrm{x}}$${)}_{5}$${\mathrm{Ge}}_{3}$${\mathrm{O}}_{11}$ single crystals for x=0 and 0.02, from 2--80 K. We consider the data in terms of a classical Debye model, and allow for the possibility of an extra low-temperature term ${C}_{\mathrm{LT}}$ and an extra high-temperature Einstein term ${C}_{E}$ (to account for extra oscillators). The data are accounted for with just the Debye model; ${C}_{\mathrm{LT}}$ and ${C}_{E}$ terms are not needed, and the implications of these results are discussed.
TL;DR: In this paper, the phonon coupling between the spins and the lattice has been used to explain the increase in the Debye temperature of Ni2+ in ZnSiF6⋅H2O.
Abstract: The measured increase in g∥ between 4 and 100 K for Ni2+ in ZnSiF6⋅H2O has been explained as a consequence of the dynamical phonon coupling between the spins and the lattice. The Debye temperature of θ=130 K previously determined from the zero‐field splitting has been found to agree with that obtained from the temperature dependence of the g value. The zero‐point vibrational correction to the g value has been deduced.
TL;DR: In this paper, it was shown that the high-temperature (1 × 1) phase of the reversible phase transition √3 × √ 3R30° 1 × 1 is not consistent with a model of a two-dimensional isotropic liquid Pb layer.
Abstract: The effect of a substrate temperature of about twice the Debye temperature on the X-ray standing-wave fields has been explored. An atomic scattering amplitude modified by the Debye-Waller factor appears to be adequate for the description of the standing-wave fields. The high-temperature standing-wave method has been applied to study the temperature dependence of Pb monolayers on Ge(111) surfaces. We obtain evidence that the high-temperature (1 × 1) phase of the reversible phase transition √3 × √3R30° 1 × 1 is not consistent with a model of a two-dimensional isotropic liquid Pb layer. Rather it appears to be composed of small islands of the original √3 × √3R30° crystalline overlayer.
TL;DR: In order to obtain a quantitative correspondence between the experimental and theoretical distributions, it is necessary to include with the usual hydrogen-bond-type potential-energy function, an effective crystal-packing force and two thermodynamical parameters of the crystal lattice, the Debye temperature and the Gruneisen constant.
Abstract: The probability distributions of the N-H...O = C and O-H...O = C hydrogen-bond lengths observed in the crystal structures of the purines, pyrimidines, nucleosides and nucleotides have been fitted to a one-dimensional hydrogen-bond potential-energy function. In order to obtain a quantitative correspondence between the experimental and theoretical distributions, it is necessary to include with the usual hydrogen-bond-type potential-energy function, an effective crystal-packing force and two thermodynamical parameters of the crystal lattice, the Debye temperature and the Gruneisen constant.
TL;DR: In this paper, the mean Debye-Waller factor and the Debye temperature were evaluated for KCl-RbCl mixed crystals with various compositions and the data used to evaluate the mean DEW factor and Debye temperatures.
Abstract: Integrated intensities of Bragg reflections have been measured for KCl-RbCl mixed crystals with various compositions and the data used to evaluate the mean Debye-Waller factors and the Debye temperatures. The composition dependence of the Debye-Waller factor is highly nonlinear with positive deviations from linearity while that of the Debye temperature is slightly nonlinear with negative deviations from linearity. Using an empirical relationship between the Debye temperature and the molar volume, the average values of the Gruneisen parameter for some mixed crystal systems are obtained.
TL;DR: In this article, the Bi-Sr-Ca-Cu-O superconductor with the nominal composition (1113) was prepared by X-ray diffraction and the resistance transition curve showed that the sample has an onset around 110K and the zero resistance temperature at 85K.
Abstract: The Bi-Sr-Ca-Cu-O superconductor with the nominal composition (1113) were prepared. An orthorhombic unit cell (a=0.544nm, b=0.543nm, c=3.07nm) was determined by X-ray diffraction. The resistance transition curve shows that the sample has an onset around 110K and the zero resistance temperature at 85K. The mutual inductance measurement also shows a two-step transition which correspond to two superconducting phases as well as that in the resistive transition. The specific heat measurement was performed in the range of 56K to 130K by continuous scanning method. A simple extrapolation of the curve was made both from below and above Tc to yield ΔC=45 mj/g.K and ΔC/Tc=0.49 mj/g.K2. From these values, the Sommerfeld constant γ and the Debye temperature θD were estimated.