Theoretical Temperature Dependence Research Articles

Phenomenological models of ferroelastics with a fully symmetric order parameter: classification by methods of equivariant catastrophe theory

Using the methods of the catastrophe theory, which take into account the symmetry of the thermodynamic system, phenomenological models of phase transitions in proper and pseudo-proper ferroelastics have been constructed for interacting order parameters, one of which is fully symmetric, invariant with respect to all symmetry transformations of the crystal. A classification of models based on the number of control parameters, which depend on external thermodynamic conditions, has been carried out. A phase diagram of one of the models has been constructed, and the theoretical temperature dependence of the heat capacity has been calculated. The comparison of theoretical and experimental data showed satisfactory qualitative agreement.

Mechanism of Boron Carbide Oxidation in a Dry Environment

ABSTRACT We analyze in detail the published experimental data on the high-temperature oxidation of compact boron carbide in dry oxygen in the range of 600–1200°C. The results of the analysis show that the oxidation of boron carbide occurs with the accumulation of excess (compared to stoichiometry) boron. Using experimental data, the time dependences of the thickness of the boron oxide melt layer formed on the sample surface during its oxidation and the mass of boron oxide evaporated from the sample surface are determined. For different temperatures, the evaporation rates of boron oxide are determined. Based on the analysis, a model of the high-temperature oxidation of compact boron carbide in dry environment was developed. Using the developed model, calculations of the process of boron carbide oxidation at different temperatures were carried out. Based on the results of calculations, the time dependences of the mass of the sample, the mass of the resulting carbon dioxide, and the thickness of the boron oxide melt layer were determined. The calculation results are compared with the experimental data and with the theoretical temperature dependence of the boron oxide melt evaporation rate, calculated using the Hertz – Knudsen equation. Based on the simulation results, it is concluded that the rates of chemical reactions are finite, and the process of B4C oxidation cannot be reduced only to oxygen diffusion through the boron oxide layer.

Phenomenological Models of Phase Transitions with Multicomponent Interacting Order Parameters: Construction and Classification by Methods of Singularity Theoryy

Phenomenological models of phase transitions for two interacting order parameters, one–component and two-component, are constructed. The construction was carried out based on the number of control parameters depending on external thermodynamic conditions by methods of the equivariant catastrophe theory (singularity theory), taking into account the symmetry of the order parameters. The classification of phenomenological models according to the number of control parameters is carried out. Phase diagrams of the models are constructed and the theoretical temperature dependence of the heat capacity is calculated, which shows a satisfactory qualitative correspondence with the experimental dependence in the Rb2KInF6 elpasolite crystal

Full polarization reversal at room temperature in unsubstituted AlN

Room temperature ferroelectricity in unsubstituted AlN films is studied to examine the role of cation substitution into wurtzite materials. AlN and (Al0.7Sc0.3)N films deposited on (111) 0.5 wt. % Nb-doped SrTiO3 have a (0001)-orientation with different in-plane lattice alignments with respect to those of the substrate, depending on the composition and the deposition temperature. The AlN films deposited at 450 °C showed complete ferroelectric switching above 140 °C but local polarization switching at room temperature because a dielectric breakdown occurred before complete switching, while full polarization reversal was observed at all measurement temperatures for (Al0.7Sc0.3)N. Low-temperature deposition, such as at 250 °C, significantly enhanced the dielectric breakdown field and also increased leakage current. As a result, sufficient polarization switching at room temperature was observed in the AlN film deposited at 250 °C. Positive-up/negative-down pulse measurements showed remanent polarization of 150 μC/cm2 and a coercive field of 8.3 MV/cm, in agreement with the theoretical value and temperature dependence observed for the AlN film deposited at 450 °C. The observed coercive field value lies on the line composed of the previously reported data in Sc concentration dependence. This tendency implies that the reduction in the coercive field is primarily attributable to the alteration of crystal lattice anisotropy caused by Sc.

Navigation-grade three-axis resonant fiber-optic gyroscope employing a multiplexed source.

A three-axis gyroscope is a vital component of an inertial measurement unit that can measure the rotation rates in three directions simultaneously. A novel three-axis resonant fiber-optic gyroscope (RFOG) configuration with a multiplexed broadband light source is proposed and demonstrated. The output light from the two vacant ports of the main gyroscope is reused as drive sources for the other two axial gyroscopes, which effectively improve the power utilization of the source. The interference between different axial gyroscopes is effectively avoided by optimizing the lengths of three fiber-optic ring resonators (FRRs) rather than by inserting other optical elements in the multiplexed link. With the optimal lengths, the influence of the input spectrum on the multiplexed RFOG is suppressed and a theoretical temperature dependence of the bias error as low as 1.08 × 10-4 °/h/°C is obtained. Finally, a navigation-grade three-axis RFOG is demonstrated with a fiber coil length of ∼100 m for each FRR.

Possible Manifestation of Q-Ball Mechanism of High-Tc Superconductivity in X-ray Diffraction

It is demonstrated, that recently proposed by the author Q-ball mechanism of the pseudogap state and high-Tc superconductivity in cuprates may be detected in micro X-ray diffraction, since it imposes inverse correlations between the size and scattering intensities of the Q-ball charge-density-wave (CDW) fluctuations in these compounds. The Q-ball charge Q gives the number of condensed elementary bosonic excitations in a CDW fluctuation of finite amplitude. The attraction between these excitations inside Euclidean Q-balls is self-consistently triggered by the simultaneous condensation of Cooper/local pairs. Euclidean Q-ball solutions, analogous to the famous Q-balls of squarks in the supersymmetric standard model, arise due to the global invariance of the effective theory under the U(1) phase rotation of the Fourier amplitudes of the short-range CDW fluctuations. A conserved ‘Noether charge’ Q along the Matsubara time axis equals Q∝TM2V, where the temperature T, Q-ball’s volume V, and fluctuation amplitude M enter. Several predictions are derived in an analytic form that follow from this picture. The conservation of the charge Q leads to an inverse proportionality between the volume V and X-ray scattering intensity ∼M2 of the CDW puddles found in micro X-ray scattering experiments. The theoretical temperature dependences of the most probable Q value of superconducting Q-balls and their size and scattering amplitudes fit well the recent X-ray diffraction data in the pseudogap phase of high-Tc cuprates.

Quantum-mechanical approach to simulation of molecular crystals thermal conductivity

This article is devoted to the implementation of scientific achievements into the educational process of physics specialties students in the framework of study course “Solid State Physics”. In this work, based on our previous scientific results, we present a quantum-mechanical approach that can adequately describe the temperature dependences of the dielectric crystals thermal conductivity. The basic provisions of quantum-mechanical approach are studied by students in the framework of university study course “Solid State Physics” and are based on Einstein and Debye classical models. This approach is based on the assumption that in dielectric crystals heat is transferred due to the phonons (Debye model) and thermal diffusion between the thermally activated neighboring quantum mechanical oscillators directly from site to site on a time scale of one-half of the oscillation period (Einstein model). In term of this consideration the thermal conductivity of molecular crystals are simulated in the framework of thermal conductivity model where heat is transferred by low-frequency phonons with taking into account phonon–rotation coupling, and above the phonon mobility edge by “diffusive” modes. For this purpose the theoretical temperature dependences of the isochoric thermal conductivity have been calculated numerically in the interval near or over the Debye temperature and compared with experimental results for solid C6H12, CHCl3 and CH2Cl2. Using simple molecular crystals as an example it is shows the dualism of the nature of heat transfer processes in the temperature region of the order of the Debye temperature and above. The obtained results will be useful for implementation in the educational process in the study course “Solid State Physics” in particular for understanding the features of heat transfer in the high-temperature range of dielectric crystals existence.

Magnetocaloric properties of a ribbon sample of Heusler alloy Ni-=SUB=-45-=/SUB=-Co-=SUB=-5-=/SUB=-Mn-=SUB=-31-=/SUB=-Al-=SUB=-19-=/SUB=-: experimental and theoretical studies

The results of experimental and theoretical studies of magnetocaloric properties of a ribbon sample of alloy Ni45Co5Mn31Al19 in the range of T=80-350 K in magnetic fields of up to 8 T are given. This alloy demonstrates a first-order magnetostructural phase transition (MSPT) in the temperature range of 270 K, as well as a second-order transition --- at the Curie temperature of 294 K. The magnetocaloric effect (MCE) was studied both by the direct method of magnetic field modulation in cyclic fields up to 8 T and by the classical extractive method. Field dependence of MCE have a different nature for first- and second-order phase transitions. A reverse MCE near MSPT is irreversible, i.e. the final sample temperature is 0.75 K below the initial one. Theoretical studies of magnetic properties and MCE of the studied sample were performed by ab initio calculations and Monte Carlo modeling. Theoretical temperature dependences of MCE are characterized by a similar interval of effect manifestation in the region of martensitic transformation and a narrower interval in the region of austenite Curie temperature as compared to the experiments, which is conditioned by the presence of a heterogeneous mixed state of austenite in the experimental sample. On the whole, theoretical data qualitatively and quantitatively reproduce the experimental dependences. Keywords: magnetocaloric effect, cyclic fields, Heusler alloy, Monte Carlo method.

Hopping conduction of non metallic heavily doped delta-layers in CVD diamond

It is shown that the experimental temperature dependence of the sheet resistance of non metallic (just below the insulator–metal phase transition) heavily boron doped delta-layers in chemically vapor deposited (CVD) diamond in a wide temperature range from 30 to 450 K can be explained by hole nearest-neighbor hopping between localized states formed probably by clusters of many negatively charged boron ions. The electrostatic potentials of these states are likely of a short-range type, which can be explained by the screening effect due to holes in neighbor clusters. The suggested theoretical temperature dependence of the sheet resistance by the choice of only two fitting parameters can be well fit to the experimental one in the whole above mentioned temperature range.

Negative nonlocal and local voltages (resistances) in a quasi-one-dimensional superconducting aluminum structure

To study a nonlocal electron transport in an aluminum superconducting quasi-one-dimensional structure, we measured negative nonlocal (local) direct current voltages in the structure in a magnetic field near the critical temperature. The structure is a normal-superconducting at Tcn<T<Tcw (Tcn and Tcw are the critical temperatures for narrow and wide wires, respectively, making up this structure). Negative voltage arises due to a quasiparticle current flowing through the N-S interface. We plotted the experimental and theoretical temperature and magnetic-field dependences of current, resistance and voltage corresponding to the peak of negative voltage, taking into account either equilibrium or nonequilibrium superconducting fluctuations.

Clumped 13CH2D and 12CHD2 compositions of methyl groups from wood and synthetic monomers: Methods, experimental and theoretical calibrations, and initial results

Methyl groups are found in numerous biogenic and synthetic materials including geologically preserved materials such as wood. The carbon and hydrogen isotope compositions of methyl groups are used as tracers in biogeochemical cycles, as paleothermometers, and to determine the hydrogen isotopic composition of ancient rain. Here we present analyses of resolved 13C–D (13CH2D) and D–D (12CHD2) clumped isotope compositions of methyl groups as new variables for the study of methyl groups in the present and past. We first present chemical methods to extract, purify, and derivatize methyl groups from methoxyl (R–O–CH3) groups as CH3F and CH3Cl, and high-resolution mass spectrometric techniques to determine the clumped isotope compositions of these species. We achieve precisions for 13C–D clumping of ±0.25‰ and D–D clumping of ±2.5‰. We anchor our clumped isotopic measurements to a thermodynamic reference frame by first calculating the theoretical temperature dependences of 13C–D and D–D clumping in CH3Cl, then placing our measurements onto this reference frame through experimental internal isotopic equilibration of CH3Cl at 200 °C. Finally, we provide and analyze an initial dataset of clumped 13C–D and D–D compositions of methyl groups from various commercial/synthetic monomers and environmental woods. We observe ranges in clumped isotope compositions of ∼11‰ in 13C–D and ∼48‰ in D–D, and systematic differences within these ranges between methyl groups from commercial monomers and wood. Specifically, commercial clumped 13C–D compositions are between 0 and 3‰, which correspond to apparent equilibrium temperatures between 170 °C and the infinite temperature limit. In contrast, the clumped 13C–D compositions of wood methoxyl groups are distinctively high (9.50–11.25‰) and 3–6‰ higher than would be expected if formed in internal isotopic equilibrium at Earth-surface temperatures. Commercial/synthetic methyl and wood methoxyl clumped D–D compositions are also distinct: −5 to +13‰ in commercial monomers vs. −35 to −8‰ in wood—such negative values cannot result from formation in isotopic equilibrium and require kinetic processes to have occurred. These results indicate that wood methoxyl groups are formed out of isotopic equilibrium and that clumped isotope compositions of methyl groups may be useful tracers of methyl group sources and sinks in the environment. For instance, isotopic clumping in methyl groups may be useful for understanding controls on isotopic clumping in methane produced by methylotrophic methanogens.

Experimental and theoretical temperature dependences of the kinetic coefficients of Bi2Te3

Experimental and theoretical temperature dependences of the kinetic coefficients of Bi2Te3

TEMPERATURE INFLUENCE ON THE MAGNETIC SENSITIVE TRANSISTOR STRUCTURES PARAMETERS

Semiconductor magnetosensitive transistor structures (MTS), as investigations have shown can be the basis of effective magnetic field sensors, as well as sensors of other physical quantities. However, the practical such sensors application requires high metrological characteristics to investigate the effect of destabilizing factors on the MTS itself. Among the basic these factors is temperature. Its influence is so noticeable that the dependence of the MTS parameters on it can be used for sensors of other physical quantities. A number of papers have been devoted to the study of the temperature influence on the MTS characteristics. However, they are non-systemic in nature and differ in the results, and do not always have sufficient comparisons with the theory and explanation of the nature and mechanisms of temperature influence. This paper sets out the task of a consistent and systematic these problems study in order to optain stronger knowledge of the temperature effect on the MTS characteristics.The experimental and theoretical temperature dependences of the drift MTS (DMTS) current transmission coefficients in the magnetic field, the coordinate of the maximum mangitosensitivity site dependence on temperature, and the dependence of the DMTS mangitosensitivity on temperature for different materials are given.The mechanisms of the temperature influence on the MTS, their characteristics dependences, in particular, the conversion parameters from the point of view of possible use in sensors, are analyzed.

Prediction of the Kinetic Properties of Sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) Solid Solution: an Ab Initio Approach

In the present paper, the interaction of electrons with different types of defects in sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) solid solution is considered. Analysis is carried out by using the short-range scattering models for electron interaction with eight kinds of point lattice defects. Calculation of the electron transition probabilities was made based on the wave function and self-consistent potential energy which were evaluated with the help of ABINIT code. For crystals with impurity concentrations 9.4 × 1014 – 1×1018 cm−3, the temperature dependencies of electron mobility and Hall factor in the range 15–1200 K are calculated. A comparative analysis of two competing approaches has been made: a short-range approach and a long-range approach (relaxation time approximation). It was found that these two approaches yield to essential qualitative and quantitative differences for theoretical temperature dependencies of electron mobility.

Study on the Melting Mechanism of Maleic Anhydride

Background: Melting of a pure crystalline material is generally treated thermodynamically which disregards the dynamic aspects of the melting process. According to the kinetic phenomenon, any process should be characterized by activation energy and preexponential factor where these kinetic parameters are derivable from the temperature dependence of the process rate. Study on such dependence in case of melting of a pure crystalline solid gives rise to a challenge as such melting occurs at a particular temperature only. The temperature region of melting of pure crystalline solid cannot be extended beyond this temperature making it difficult to explore the temperature dependence of the melting rate and consequently the derivation of the related kinetic parameters. Objective: The present study aims to explore the mechanism of the melting process of maleic anhydride in the framework of phase transition models. Taking this process as just another first-order phase transition, occurring through the formation of nuclei of new phase and their growth, particular focus is on the nucleation and growth models. Methods: Non-isothermal thermogravimetry, as well as differential scanning calorimetry studies, has been performed. Using isoconversional kinetic analysis, temperature dependence of the activation energy of melting has been obtained. Nucleation and growth models have been utilized to obtain the theoretical temperature dependencies for the activation energy of melting and these dependencies are then compared with the experimentally estimated ones. Conclusion: The thermogravimetry study indicates that melting is followed by concomitant evaporation, whereas the differential scanning calorimetry study shows that the two processes appear in two different temperature regions, and these differences observed may be due to the applied experimental conditions. From the statistical analysis, the growth model seems more suitable than the nucleation model for the interpretation of the melting mechanism of the maleic anhydride crystals.

A dielectric model of thawed and frozen Arctic soils considering frequency, temperature, texture and dry density

ABSTRACTA dielectric model was developed for thawed and frozen mineral soils, based on the refractive mixing dielectric formula and the dielectric measurement data for three soils collected in the Arctic tundra of the Yamal Peninsula. The refractive mixing dielectric model was used in conjunction with the Debye multi relaxation equations as a theoretical model to fit the measured complex relative permittivity spectra as a function of soil moisture and temperature. As a result, the dielectric spectroscopic parameters for the various components of water in the soil, such as the low- and high-frequency limits of the complex relative permittivity, the times of the corresponding relaxations, and the specific conductivity, were simultaneously determined for soils with different clay contents for all measured temperatures. As the theoretical temperature dependences of these parameters, the Clausius–Mossotti, Eyring, and linear equations for the conductivity were used. By using approximations of the measured data with these formulas, the parameters of the temperature-dependent model were derived, such as the coefficient of volume expansion, energy and entropy of activation, and coefficient of thermal conductivity. A set of the parameters discussed above in conjunction with the refractive mixing formula is a temperature- and mineralogically dependent multi-relaxation spectroscopic dielectric model, which enables estimation of the permittivity of moist soils as a function of dry soil density, moisture, frequency, temperature, and texture. The statistical error of the proposed dielectric model was estimated in terms of the normalized root-mean-square error (nRMSE), which was equal to 5% and 25% for the dielectric constant and dielectric loss factor, respectively.

Constructing and Classifying Phenomenological Models of Phase Transitions by Means of Catastrophe Theory

Phenomenological models of phase transitions for two- and three-component order parameters are constructed by means of catastrophe theory using equivariant vector fields that consider the symmetry of the thermodynamic system. The models are classified according to the number of control parameters, depending on external thermodynamic conditions. Phase diagrams of some models are constructed and theoretical temperature dependences of their thermal properties are calculated. A comparison of theoretical and experimental data show a satisfactory match in quality.

The Analytical Solution of Incomplete Gamma Function to Determine the Electrical Resistivity at Normal State for MgB2 Superconductor

In the present study, the series representation of the generalized incomplete Gamma function is described. The theoretical results achieved by calculating the incomplete Gamma function are in agreement with the experimental data of the previous reports as discussed in this study. At different integer values of m, the generalized Bloch-Gruneisen function is presented in this work. The theoretical temperature dependence of resistivity at normal state correlates the experimental outcomes for pristine MgB2 superconductor under the range of 40 – 175K. In addition, the incomplete Gamma function that has proposed for the evaluation of temperature dependence of resistivity reveals the validity and precision of the method.

Classification of Phenomenological Models of Phase Transitions with Three-Component Order Parameters by Methods of Catastrophe Theory: $$L = {T_d}(\bar 43m)$$

Using the equivariant catastrophe theory, we classify phenomenological models of phase transitions with a three-component order parameter and with a number of control parameters from one to four. The analysis of phase diagrams of the obtained models shows that the description of all low-symmetry phases requires fewer terms of the power-series expansion than that required by the model constructed using the traditional method taking all terms up to the 2nth power into account (n > 1). The theoretical temperature dependence of the heat capacity is compared with the experimental data in the GaV4S8 compound.

Solid-Oxide Electrochemical Cell for Determining the Diffusion of Hydrogen in Nitrogen at High Temperatures

Procedure was developed for measuring the diffusion coefficient of hydrogen in its mixture with nitrogen in the temperature range 450–600°C under atmospheric pressure. This is done in an electrochemical cell based on a solid-oxide electrolyte with proton conductivity of composition BaCe0.7Zr0.1Y0.2O3–δ. The procedure makes it possible to trace how the hydrogen diffusion coefficient varies with temperature and hydrogen concentration in nitrogen. It is shown that the hydrogen diffusion coefficient grows with increasing hydrogen concentration, its temperature dependence is of power-law type with n = 1.5, and it is in satisfactory agreement with the theoretical temperature dependence