Effective Debye Temperature Research Articles

Erratum to “Acoustic wave velocities and effective Debye temperature in potassium alum KAl(SO4)2·12H2O crystal”[Solid State Sci. 154 (2024) 107595]

Erratum to “Acoustic wave velocities and effective Debye temperature in potassium alum KAl(SO4)2·12H2O crystal”[Solid State Sci. 154 (2024) 107595]

Thermoacoustical study of intermolecular interactions in binary liquid mixtures of benzaldehyde with methanol and ethanol

Density (ρ) and ultrasonic velocity (u) for the binary mixtures of benzaldehyde with methanol and ethanol have been observed experimentally at 293, 303 and 313 K over the different compositions. The data so obtained was employed for the computation of specific heat ratio (γ), heat capacity (CP), effective Debye temperature (θD) and pseudo-Grüneisen parameter (Γ) excess pseudo-Grüneisen parameter (ΓE), excess molar volume (VmE) and excess isentropic compressibility (Δks) which were further endorsed to the Redlich-Kister polynomial equation. Excess parameters were graphed with the varying mole fraction of benzaldehyde and further considered for examining the nature and extent of molecular interaction in these two types of binary mixtures. The excess parameters with negative values in the observations were elaborated in terms of interaction between molecules of the constituents of the mixtures. The observed ultrasonic velocity and density were also fitted in first order polynomial equation. This research proves that the interaction between benzaldehyde and methanol is stronger than benzaldehyde and ethanol.

Photoconductivity study of Ca2Si epitaxial film on Si(111) substrate

Semiconductor calcium semi-silicide (Ca2Si) with a complex crystal and energy band structure is theoretically characterized by a direct fundamental transition, which is difficult to identify experimentally in Ca2Si films due to high absorption at defect levels. The study of the temperature dependences of photoconductivity in Ca2Si epitaxial films is one of the methods for assessing both the nature of the fundamental transition and a number of thermodynamic parameters. In this work, photoconductivity was firstly observed in an epitaxial Ca2Si film grown on a Si(111) substrate in the temperature range from 10 K to 300 K. Based on an analysis of the parameters of three thermodynamic models, the existence of a direct fundamental transition Eg = 1.195 eV at 0 K was proved, and the effective phonon energy (<Eph>), the Einstein (Ξ) and Debye (ΘD) temperatures, as well as the electron-phonon coupling constant, and the hole mobility were determined.

Effective Debye Temperature and Quasi-Crystalline Behavior of Water at Elevated Pressure and in the Temperature Range: 353.15 K to 473.15 K

Based on quasi-crystalline model for liquids, Debye temperature for water has been estimated in the high-pressure region (0.25 GPa -3.5 GPa) and temperature range: T=353.15 K to T=473.15 K. The obtained results infer that Debye temperature changes to a greater extent as the pressure increases from 0.25 G Pa to 3.5 G Pa, whereas no significant increase is observed with increase in temperature from 353.15 K to 473.15 K. The reasonable values of θD (~180 K to 423 K) are the strong evidence of existence of effective Debye temperature and quasi-crystalline state in water at elevated pressure. Present study also indicates that molecular motion of water is more sensitive to increase in pressure rather than increase in temperature.

Quasi-Crystalline Behavior of Imidazolium Based Pure Ionic Liquids Over the Extended Pressure Range

Based on quasi-crystalline model for liquids, Debye temperature, Bayers number, and Pseudo Gurnasien parameter for three pure Imidazolium based ionic liquids with same anion have been estimated in the elevated pressure range (1.83 MPa -59.59 MPa) and temperature range (298.15 K – 328.15 K). The reasonable values of θD (~ 48.58 K – 56.30 K) are the evidence of existence of effective Debye temperature and quasi-crystalline state in ionic liquids at elevated pressure whereas slight change in the values of these parameters indicate that molecular motion is more sensitive to increase in pressure rather than increase in temperature in the given ionic liquids under study. Marginal change in the values of Debye temperature, Bayers number, and Pseudo Gurnasien parameter with increase in alkyl change of cation indicate that alkyl chain of cation is not accountable to study the quasi-crystalline behavior of the given ILs in the given pressure and temperature range.

Surface and dynamical properties of GeI2

GeI2 is an interesting two-dimensional wide-band gap semiconductor because of diminished edge scattering due to an absence of dangling bonds. Angle-resolved x-ray photoemission spectroscopy indicates a germanium rich surface, and a surface to bulk core-level shift of 1.8 eV in binding energy, between the surface and bulk components of the Ge 2p3/2 core-level, making clear that the surface is different from the bulk. Temperature dependent studies indicate an effective Debye temperature () of 186 ± 18 K for the germanium x-ray photoemission spectroscopy feature associated with the surface. These measurements also suggest an unusually high effective Debye temperature for iodine (587 ± 31 K), implying that iodine is present in the bulk of the material, and not the surface. From optical absorbance, GeI2 is seen to have an indirect (direct) optical band gap of 2.60 (2.8) ± 0.02 (0.1) eV, consistent with the expectations. Temperature dependent magnetometry indicates that GeI2 is moment paramagnetic at low temperatures (close to 4 K) and shows a diminishing saturation moment at high temperatures (close to 300 K and above).

Shell-model and first-principles calculations of vibrational, structural and ferroelectric properties of KH2PO4

We develop a shell model (SM) for potassium dihydrogen phosphate (KDP) which is fitted to ab initio (AI) results that include nonlocal van der Waals corrections. The SM is comprehensively tested by comparing results of structural, vibrational and ferroelectric properties with AI and experimental data. The relaxed structural parameters are in very good agreement with the AI results and the available experimental data. The Γ-point phonons and the total phonon densities of states (DOSs) in the ferroelectric and paraelectric phases calculated with the developed SM are in good overall agreement with the corresponding AI and experimental data. We also compute the effective Debye temperature as a function of T which shows good accordance with the corresponding AI and experimental results. Classical molecular dynamics (MD) simulations obtained with the developed SM show a FE-PE phase transition at ≈ 360 K in remarkable agreement with ab initio MD calculations.

Effective Debye temperature of ionic liquids and their binary mixtures

Assuming the quasicrystalline structure to ionic liquids the effective Debye temperature of seven pure ionic liquids (H2O, DEAA, DEAS, TEAA, TEAS, TMAA, and TMAS.) has been calculated. Further, the model has been extended to six binary mixtures of (DEAA + H2O, DEAS + H2O, TEAA + H2O, TEAS + H2O, TMAA + H2O, and TMAS + H2O.). This is our first attempt in the study of thermal properties of pure ionic liquids and their binary mixtures. The concept of excess Debye temperature (θDE) has been introduced and correlated with interactions in ionic liquid systems. The input data desired are density, sound speed, heat capacity and ratio of heat capacities (CP/CV).

X-ray photoemission studies of BiInO3: Surface termination and effective Debye temperature

BiInO3 is a potentially polar oxide with distinct optical properties whose origin could result from a surface that has not been well characterized. The surface properties of BiInO3 thin films have been characterized here by temperature dependent angle-resolved x-ray photoemission spectroscopy. A large surface to bulk core-level binding energy shift for the In 3d5/2 core-level is identified, indicating a surface very different from the bulk. BiInO3 terminates in indium oxide and loses bismuth from the surface of the film at T = 573 K. The Debye–Waller plots suggest effective Debye temperatures of 263 ± 10 and 556 ± 27 K for the surface and bulk components of In 3d core-level, respectively.

Nonuniform Debye Temperatures in Quasi-One-Dimensional Transition-Metal Trichalcogenides

The Debye–Waller factor plots for S 2p core-level, based on temperature-dependent X-ray photoemission measurements on quasi-one-dimensional (1D) chains of TiS3, suggest effective Debye temperatures...

Computation of Effective Debye Temperature of Liquid Metal Alloys

Computation of Effective Debye Temperature of Liquid Metal Alloys

Physicochemical parameters of the binary mixtures of formamide/N-methylformamide with 2-chloroethanol at different temperatures

ABSTRACT The pseudo-Gruneisen parameter , effective Debye temperature, acoustic nonlinearity parameter , internal pressure and isobaric thermal expansion coefficient have been evaluated for binary liquid mixtures of formamide (FA) and N-methylformamide (NMF) with 2-chloroethanol (2Cl-OH) at 298.15 K, 308.15 K and 318.15 K, over the entire concentration range. The excess pseudo-Gruneisen parameter , excess effective Debye temperature , excess nonlinearity parameter, excess internal pressure and excess isobaric thermal expansion coefficient were also calculated. The calculated values are reasonably satisfactory with the experimental results on sound propagation data of liquid mixtures. These physicochemical parameters play an important role in understanding of the significance of anharmonic and nonlinear behaviour with regard to intermolecular interactions in the liquid mixtures.

Indium segregation to the selvedge of In4Se3 (001)

Thermal motion of the surface atoms will lead to a decrease in photoemission intensity, while surface segregation may result in an increase of some phostoemission intensities. For In4Se3(001), both effects are seen. The Debye–Waller factor plot, based on the temperature dependent X-ray photoemission spectroscopy (XPS) measurements on In4Se3(001), suggests an upper bound of 203 ± 6 K for the effective Debye temperature, based on the surface component of the In 3d5/2 core-level. Indium is found to segregate to selvedge (subsurface region) of the crystal.

Computational Study of Debye Temperature for Liquid Mixtures-Thermal Energy Variations

In an analytical way effective Debye temperature computations of functional materials are extended to organic liquid mixtures using ultrasonic velocity and density measurements. Thermal properties of organic liquid mixture containing Aniline + Toluene, Aniline + o-Xylene and Aniline + Mesitylene over different mole fractions have been explained using Debye temperature variations and they are scrutinized to bring out the molecular association due to thermal energy changes of binary liquid mixtures. The results including computation of Debye temperatures using standard formula, ideal mixture relation and modified Lorentz-Bertholet combination mixing rule and their deviations are used to explain thermal energy changes of component molecules in liquid mixtures and their association.

Acoustical effective Debye temperature studies in heterocyclic aromatic functional materials of organic liquid mixtures at four different temperatures T = (303.15, 308.15, 313.15 and 318.15) K

Abstract Debye temperature and Surface tension are theoretically estimated for binary liquid mixtures of heterocyclic aromatic compound Quinoline and m-Xylene using ultrasonic velocity & density measurements over entire mole fraction of Quinoline at different temperatures. An analogy of Debye temperature along with the Viscosity and Surface Tension variations are scrutinized to bring out the molecular contribution to thermal energy changes of binary liquid mixtures. The observed and obtained results are used to explain the molecular association and thermal behaviour between the component molecules of liquid mixtures.

The Debye Temperature of a Single Crystal Thorium–Uranium Dioxide Alloy

The effective Debye temperature () of the surface of a single crystal of U0.71Th0.79O2 alloy prepared by hydrothermal synthesis is obtained from temperature‐dependent X‐ray photoemission in the temperature range of 300–623 K. The effective average Debye temperature is determined to be 217 ± 24 K. X‐ray fluorescence (XRF) spectroscopy confirms the crystal's composition as U0.71Th0.79O2. Photoemission spectroscopy reveals both thorium and uranium 4f states, which includes uranium and thorium in 4+ oxidation states. The Debye temperature of the single crystal U0.71Th0.79O2 alloy, as measured via photoemission, is lower than urania or thoria literature values, indicating either higher defect scattering or the presence of added vibrational modes within the alloyed sample.

Modulating temperature dependence of thermal conductivity by nanostructuring

At around room temperature and higher, thermal conductivity of single crystal commonly decreases as temperature increases and shows negative temperature dependence. Crystals with positive temperature dependence, which is often preferred in thermal management, requires high Debye temperature. While this narrows the selection of material candidate, the effective Debye temperature can be enhanced through nanostructuring the single crystals. By investigating heat conduction in nanocrystalline silicon, silicon carbide, and diamond, we here demonstrate that shift of temperature dependence of heat capacity and decrease in magnitude of negative temperature dependence of relaxation time by nanostructuring lead to positive temperature dependence of thermal conductivity.

Rotationally Free and Rigid Sublattices of the Single Crystal Perovskite CH3NH3PbBr3 (001): The Case of the Lattice Polar Liquid

The dynamic motion, within the lattice of single crystal CH3NH3PbBr3 (001) hybrid halide perovskite, was investigated using powder and single crystal X-ray diffraction, and X-ray photoemission spectroscopy. Single crystal X-ray diffraction studies indicate the methylammonium cation adopts multiple orientations within the crystal, at room temperature, evidence of a disordered methylammonium sublattice within a rigid and ordered PbBr3 matrix lattice. From the Br 3d5/2 core level photoemission temperature dependence, an effective Debye temperature of 160 ± 22 K can be estimated, while the Pb 4f7/2 core-level Debye–Waller factor plots suggest an effective Debye temperature of 202 ± 131 K, indicative of a very rigid lattice along the (001) direction. The combination of X-ray diffraction with temperature dependent X-ray photoemission spectroscopy for bromine and lead core level peaks supports the characterization of CH3NH3PbBr3 as a lattice polar liquid crystal, as CH3NH3PbBr3 does not meet the criteria require...

Luminescence Anisotropy and Thermal Effect of Magnetic and Electric Dipole Transitions of Cr3+ Ions in Yb:YAG Transparent Ceramic.

In this article, we present an in-depth optical study on luminescence spectral features and the thermal effect of the magnetic dipole (MD) transitions (e.g., the R lines of 2E → 4A2) and the associated electric dipole transitions (e.g., phonon-induced sidebands of the R lines) of Cr3+ ions in ytterbium-yttrium aluminum garnet polycrystalline transparent ceramic. The doubly split R lines predominately due to the doublet splitting of the 2E level of the Cr3+ ion in an octahedral crystal field are found to show a very large anisotropy in both emission intensity and thermal broadening. The large departure from the intensity equality between them could be interpreted in terms of large difference in coupling strength with phonons for the doubly split states of the 2E level. For the large anisotropy in thermal broadening, very different effective Debye temperatures for the two split states may be responsible for it. Besides the 2E excited state, the higher excited states, for example, 4T1 and 4T2 of the Cr3+ ion, also exhibit a very large inequality in coupling strength with phonons at room temperature. By examining the Stokes phonon sidebands of the MD R lines at low temperatures with the existing ion-phonon coupling theory, we reveal that they indeed carry fundamental information of phonons. For example, their broad background primarily reflects Debye density of states of acoustic phonons. These new results significantly enrich our existing understanding on interesting but challenging luminescence mechanisms of ion-phonon coupling systems.

The lattice stiffening transition in UO2 single crystals

The effective Debye temperatures () of the surface region of UO2 single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K–623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500 ± 59 K below 475 K and 165 ± 21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO2 Debye temperature, with the changes in the lattice expansion coefficient for UO2, support strong lattice-phonon interaction arising from the Jahn–Teller distortion.