Finite temperature thermophysical properties of MgCu intermetallic compound from quasi-harmonic Debye model

The influence of pressure and temperature on the thermodynamic properties of MgCu intermetallic compound was investigated by quasi-harmonic Debye model approximation.The equation of state(EoS)parameters has performed using plane-wave pseudopotential(PW-PP)approach in the framework of the density functional theory(DFT)and the generalized gradient approximation(GGA)for the exchange-correlation functional.Our results agree well with other data of the literature.The finite temperature thermophysical properties under pressure up to 16 GPa and high temperature up to 800 K,respectively were determined.Our results of the thermophysical properties are also agree very well with other data of the literature,where for example at ambient temperature,the deviation between our obtained value(11.05 Cal mol^(−1)K^(−1))of C V,and the theoretical value(11.21 Cal mol^(−1)K^(−1))reported in the literature is only around 1.44%.The finite temperature thermophysical properties were found varied monotonically with either temperature or pressure.Compared with other materials previously studied,similar behaviors were observed.

Thermodynamics and elastic properties of Ta from first-principles calculations

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties of Ta, including phonon density of states （DOS）, equation of state, linear thermal expansion coefficient, entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young＇s modulus, microhardness, and sound velocity, are studied using the first-principles projector-augmented wave method. The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon DOS and the Debye model. The thermal electronic contribution to Helmholtz free energy is estimated from the integration over the electronic DOS. By comparing the experimental results with the calculation results from the first-principles and the Debye model, it is found that the thermodynamic properties of Ta are depicted well by the first-principles. The elastic properties of Ta from the first-principles are consistent with the available experimental data.

Study of the properties of non-gas dielectric capacitors in porous media

The size of pores and throats is at the nano- meter scale in tight oil and shale gas zones, and the resistivity of these reservoirs is very high, so the reservoirs show more dielectric properties than conductivity proper- ties. The conductive and dielectric characteristics of a parallel plate capacitor full of fresh water, NaCl solutions, and solid dielectrics, for example, sands are investigated in this paper, and the capacitance data of the non-gas capacitor are measured at different salinities and frequencies by a spectrum analyzer. The experimental results illustrate that the capacitance of this kind of capacitor is directly pro- portional to the salinity of the solutions and inversely proportional to the measuring frequency, the same as a vacuum parallel plate capacitor. The remarkable phenom- enon, however, is that the capacitance is inversely pro- portional to the square of the distance between two plates. The specific characteristic of this capacitor is different from the conventional parallel plate capacitor. In order to explain this phenomenon, the paper proposed a new concept, named ＂single micro ion capacitor＂, and established a novel model to describe the characteristics of this particular capacitor. Based on this new model, the theoretical capacitance value of the single micro ion capacitor is calculated, and its polarization and relaxation mechanisms are analyzed.

Thermodynamic properties of 3C-SiC

In the present paper, we report on the results of various thermodynamic properties of 3C-SiC at high pressure and temperature using first principles calculations. We use the plane-wave pseudopotential density functional theory as im- plemented in Quantum ESPRESSO code for calculating various cohesive properties in ambient condition. Further, ionic motion at a finite temperature is taken into account using the quasiharmonic Debye model. The calculated thermody- namic properties, phonon dispersion curves, and phonon densities of states at different temperatures and structural phase transitions at high pressures are found to be in good agreement with experimental and other theoretical results.

First-principles calculations on the elastic and thermodynamic properties of NbN

The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory （DFT）. The generalized gradient approximation （GGA） with the Perdew-Burke Ernzerhof （PBE） method is used to describe the exchange-correlation energy in the present work. The calculated equilibrium lattice constant a0, bulk modulus B0, and the pressure derivative of bulk modulus B~ of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data. The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model, in which the phononic effect is considered, the relations of （V - Vo）/Vo to the temperature and the pressure, and the relations of the heat capacity Cv and the thermal expansion coefficient α to temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K. At low temperature, Cv is proportional to T3 and tends to the Dulong Petit limit at higher temperature. We predict that the thermal expansion coefficient α of NbN is about 4.20 × 10-6/K at 300 K and 0 GPa.

Large Scale Analysis of Complex Permittivity of Breast Cancer in Microwave Band

To obtain some prior knowledge of breast cancer detection by microwave imaging, we have measured and analyzed the complex permittivity of tissues extracted from over 140 breast cancer surgeries. The relative permittivity and conductivity of tumor at 1.6 GHz were 17.5% and 16.2% higher than those of mammary gland tissue, respectively. In invasive ductal carcinoma of scirrhous type, 8 out of 64 had higher relative permittivity and conductivity of mammary gland than those of tumor. However, when evaluated by the Debye parameter considering the frequency dependence of the tissue, it is rare that ε∞ and Δε of cancer are simultaneously lower than those of mammary gland. The relative permittivity and conductivity of fibroadenoma are almost the same as those of mammary glands. The relative permittivity and conductivity of each tissue showed strong linearity. Microwave imaging requires accurate reconstruction of ε∞ and Δε to distinguish cancer from normal tissue.

Thermoelasticity of CaO from first principles

The thermoelastic properties of CaO over a wide range of pressure and temperature are studied using density functional theory in the generalized gradient approximation. The transition pressure taken from the enthalpy calculations is 66.7 GPa for CaO, which accords with the experimental result very well. The athermal elastic moduli of the two phases of CaO are calculated as a function of pressure up to 200 GPa. The calculated results are in excellent agreement with existing experimental data at ambient pressure and compared favourably with other pscudopotential predictions over the pressure regime studied. It is also found that the degree of the anisotropy rapidly decreases with pressure increasing in the B1 phase, whereas it strongly increases as the pressure increases in the B2 phase. The thermodynamic properties of the B1 phase of CaO are predicted using the quasi-harmonic Debye model; the heat capacity and entropy arc consistent with other previous results at zero pressure.

First principle calculation of elastic and thermodynamic properties of stishovite

Using ab initio plane-wave pseudo-potential density functional theory method, the elastic constants and band structures of stishovite were calculated. The calculated elastic constants under ambient conditions agree well with previous experimental and theoretical data. C13, C33, C44, and C66 increase nearly linearly with pressure while C11 and C12 show irregularly changes with pressure over 20 GPa. The shear modulus （Cll-C12）/2 was observed to decrease drastically between 40 GPa and 50 GPa, indicating acoustic mode softening in consistency with the phase transition to CaC12-type structure around 50 GPa. The calculated band structures show no obvious difference at 0 and 80 GPa, being consistent with the high incompressibility of stishovite. With a quasi-harmonic Debye model, thermodynamic properties of stishovite were also calculated and the results are in good agreement with available experimental data.

Structural, Anisotropic and Thermodynamic Properties of Imm2-BCN

Structural, anisotropic, and thermodynamic properties of Imm2-BCN were studied based on density function theory with the ultrasoft psedopotential scheme in the frame of the generalized gradient approximation（GGA）. The elastic constants were confirmed that the predicted Imm2-BCN is mechanically stable. The anisotropy of elastic properties were also studied systematically. The anisotropy studies of Young＇s modulus, shear modulus, linear compressibility, and Poisson＇s ratio show that the Imm2-BCN exhibits a large anisotropy. Through the quasi-harmonic Debye model, the relations between the equilibrium volume V, thermal expansion α, the heat capacity C_V and CP, the Grüneisen parameter γ, and the Debye temperature Θ_D with pressure P and temperature T were also studied systematically.

Extraction of optical constants in the terahertz band using material dispersion models

This study proposes a method based on material dispersion models to computationally simulate terahertz(THz)time-domain spectroscopy signals.The proposed method can accurately extract the refractive indices and extinction coefficients of optically thin samples and high-absorption materials in the THz band.This method was successfully used to extract the optical constants of a 470-μm-thick monocrystalline silicon sample and eliminate all errors associated with the Fabry-Perot oscillation.When used to extract the optical constants of a 16.29-mm-thick polycarbonate sample,our method succeeded in minimizing errors caused by the low signal-to-noise ratio in the extracted optical constants.

LDA＋U calculation of structural and thermodynamic properties of Ce2O3

We investigated the structure and thermodynmnic properties of the hexagonal Ce2O3 by using LDA＋U scheme in the fi＇ame of density functional theory （DFT）, together with the quasi-harmonic Debye model. The obtained lattice constants, bulk modulus, and the insulating gap agree well with the available experimental data. We successfully yielded the temperature dependence of bulk modulus, volume, thermal expansion coefficient, Debye temperature, specific heat as well as the entropy at different U values. It is found that the introduction of the U value cannot only correct the calculation of the structure but also improve the accurate description of the thermodynamic properties of Ce2Oa. When U = 6 eV the calculated volume （538 Bohra） at 300 K agrees well with the experimental value （536 Bohr3）. The calculated entropy curve becomes more and more close to the experimental curve, with the increasing U value.