Temperature Dependence Research Articles

Intrinsic Temperature Dependence of Raman-Active Modes in Individual Isolated Single- and Double-Walled Carbon Nanotubes.

The intrinsic temperature dependence of Raman-active modes in carbon nanotubes (CNTs), particularly the radial breathing mode (RBM), has been a topic of a long-standing controversy. In this study, we prepared suspended individual CNTs to investigate how their Raman spectra depend on temperature and to understand the effects of environmental conditions on this dependency. We analyzed the intrinsic temperature dependence of the main Raman-active modes, including the RBM, the moiré-activated R feature, and the G-band in double-walled carbon nanotubes (DWCNT) and single-walled carbon nanotubes (SWCNTs) after complete desorption of air. The inner tube of the DWCNT, like the desorbed SWCNTs, was free from environmental influences, resulting in minimal temperature-induced RBM frequency shifts. We show that the larger RBM shift of SWCNTs upon initial heating is not intrinsic but is due to air desorption. The R feature, attributed to moiré-activated phonon scattering and nondispersive in nature, demonstrated a quasi-linear temperature dependence, akin to the G-band but with a lower temperature coefficient. The G-band, which was largely unaffected by environmental conditions, exhibited a consistent temperature coefficient across SWCNTs, DWCNTs, and small SWCNT bundles.

Compensation of temperature drift of a ring laser gyroscope

The paper investigates methods and algorithms for compensating the temperature drift of the angular velocity signal. The influence of the design on the properties of the laser gyroscope is examined. A mathematical model and algorithm for compensating the temperature dependency of the output signal of the laser gyroscope are proposed.

DRIFT MOBILITY OF ELECTRONS IN INDIUM ANTIMONIDE IN THE WEAK ELECTRIC FIELD REGIME

In scientific publications, theoretical and experimental studies of the Hall mobility of indium antimonide are presented; its dependence on temperature, charge carrier concentration, and electric field strength. Note that a typical form of the weak-field temperature dependence of the electron drift mobility, showing its behavior in a wide range of temperature and impurity atom concentration, is not presented. The processes of charge carrier scattering in indium antimonide are poorly represented. The aim of this work is a detailed study of the main mechanisms of electron scattering in indium antimonide, the temperature dependence of the weak-field electron mobility in a wide range of the semiconductor doping degree. A quantitative assessment of the electron scattering rates in indium antimonide is given for the main types of impurity and phonon mechanisms. A detailed analysis of the scattering processes is carried out. It is emphasized that a difference in the scattering rates in the Г- and L-valleys of the conduction band is observed. Scattering by ionized impurity atoms determines the resulting scattering velocity up to 40 K. At temperatures above 40 K, the role of polar optical scattering in the Г-valley increases significantly, practically determining the behavior of the resulting velocity. In the L-valleys, the greatest contribution is made by 2 types of phonon scattering: acoustic and polar optical. Based on the obtained scattering process modeling results, the temperature dependence of the weak-field drift mobility in the Г- and L-valleys was calculated. From the simulation results it is clear that the mobility of electrons in the Г-valley exceeds the corresponding values in the L-valleys by 2 – 4 orders of magnitude. The resulting mobility is determined taking into account the valley population. From the results of modeling the drift mobility it is clear that the area of its increase is determined by the processes of scattering by impurity ions. The higher the doping degree of the semiconductor, the lower the electron mobility. With a further increase in temperature, the mobility decreases. A characteristic feature of the typical temperature dependence of the weak-field electron mobility in InSb is that at high temperatures its behavior is determined by scattering processes on polar optical phonons. A set of modeling parameters has been determined that ensure compliance with experimental data.

Исследование щелевой структуры сверхпроводящего поликристаллического пниктида недодопированного состава BaFe2-xNixAs2 с x = 0.07

We studied the superconducting energy parameters of underdoped polycrystalline BaFe1.93Ni0.07As2 pnictide with Tc ≈ 18.5 K synthesized via a novel method. Using incoherent multiple Andreev reflection effect spectroscopy, we directly determined the magnitudes of two microscopic superconducting order parameters: the small superconducting gap and a possibly large anisotropic gap in the k-space, their characteristic ratios and temperature dependences. The calculated temperature dependences of the superconducting gaps, calculated using the model written by Moskalenko and Suhl for two effective superconducting condensates fits well with the experimental data. A resonant interaction of the superconducting subsystem with a characteristic bosonic mode has been observed and the boson energy at T << Tc was determined.

Terahertz Time-Domain Spectroscopy of Substituted Gadolinium Gallium Garnet

Temperature dependence of the lowest frequency transverse optical phonon (TO1) in a single crystal Substituted Gadolinium Gallium Garnet (SGGG, (001)) was studied using terahertz time-domain spectroscopy at temperatures between 80 K and 500 K. The complex dielectric constants were calculated from the optical constants fitting with the Lorentz oscillator model. The results show that the TO1 phonon of SGGG is at 2.5 THz at room temperature, the frequency of the TO1 phonon slightly decreases, and the dumping factor clearly increases with increasing temperature. Additionally, our results demonstrate that even a small substitution can induce a phonon shift, leading to higher absorption and causing a slight degradation in thermal stability. Our work is expected to support the development of magneto-optical and spintronic devices.

КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССОВ ТЕПЛООБМЕНА

The article considers mathematical models of calculation of thermal conductivity in a constant cross-section rod, change of a liquid temperature along the length of the pipe and calculation of two-dimensional temperature field of liquid under the flow in the pipe. The mathematical model of fluid flow in the tube is realized in the form of a program for computers. The results of modeling of processes of heat conduction and heat exchange are presented. The task of simulation of heat exchange processes using numerical method of solving the Cauchy problem in the form of finite differences is considered in detail. This approach makes it possible to calculate the value of the studied parameter at any point of the object under investigation. The numerical method involves obtaining a system of algebraic equations for unknown variables and an algorithm for solving these equations. The main dependencies describing the process of thermal conductivity in the rod of the final length are given. The results of the calculation of the temperature change by the length of the rod are presented in a graphical presentation. The main dependencies describing the process of temperature change of the liquid flowing through the pipe are given. The results of the calculation of temperature pressure change over the length of the pipe are presented in a graphical presentation. The problem statement and mathematical model of the process of flow of incompressible liquid in the pipe are considered in detail. On the basis of the developed mathematical model, a computer model, implemented in the form of a program for computers, was created. The results of calculation, using the method of running, of two-dimensional temperature field of liquid along the pipe length are presented. The temperature dependence of the liquid in the various nodal points of the pipe section along the length of the pipe is presented in a graphical form.

Theoretical Study of the Stability of CdSn Liquid Alloy at Different Temperatures

The quasi-lattice theory (QLT) is utilized for the prediction of the temperature and concentration dependence of the thermodynamic properties of the molten CdSn alloys. At first, the analytical expressions are employed to reckon the excess Gibbs free energy of mixing, Gibbs free energy of mixing, activity, enthalpy of mixing and entropy of mixing as well as concentration fluctuations, short range-order parameter and excess stability function ofCdSn melts at 773 K. For this, the model parameters i.e. size ratio and order energy parameter are assessed using the experimental data of the free energy of mixing for CdSnmelts at 773 K. The theoretical values of the thermodynamic functions are in well harmony with the interrelated experimental values. The theoretical values of the structure function like concentration fluctuations are in unison with the experimental values for molten CdSn system at 773 K. Again, the optimization procedure is applied to explore the excess Gibbs free energy of mixing, activity, concentration fluctuations, short-range order parameter and excess stability function at different temperatures for CdSnmelts. The present study discloses that the stability as well as the segregating nature of CdSnmelts decrease with the elevation of the temperature from 773 K to 1123 K. Further, the temperature dependency of the excess stability function reveals that there is a probability of transition from segregating character to the ordering character of CdSn melts near 1162 K. Keywords: Gibbs free energy of mixing; entropy of mixing; concentration fluctuations; short-range order parameter; excess stability function

Visualization of the 3D Structure of Subcritical Aqueous Ca(NO3)2 Solutions at 25~350 °C and 40 MPa by Raman and X-Ray Scattering Combined with Empirical Potential Structure Refinement Modeling

Raman scattering measurements were performed on 1 mol dm−3 aqueous calcium nitrate (Ca(NO3)2) and sodium nitrate (NaNO3) solutions containing 4% (w/w) D2O in a temperature range from 25 to 350 °C and pressure of 40 MPa. As the temperature increased, the N–O symmetric stretching vibrational band (ν1) of NO3− at 1045–1047 cm−1 shifted to a lower wavenumber by 5~6 cm−1. The band analysis using one Lorentzian component showed that the full-width at half maximum (FWHM) did not change significantly below 175 °C but increased rapidly above 200 °C for both solutions. The peak area for an aqueous Ca(NO3)2 solution showed a breakpoint between 225 and 250 °C, suggesting a change in the coordination shell of NO3− at 175~250 °C. The OD symmetric stretching vibrational band of HDO water was deconvoluted into two Gaussian components at 2530 and 2645 cm−1; the former component has high temperature dependence that is ascribed to the hydrogen bonds, whereas the latter one shows less temperature dependence due to the non-hydrogen bonds of water. X-ray scattering measurements were performed on a 1 mol dm−3 aqueous Ca(NO3)2 solution at 25 to 210 °C and 40 MPa. Empirical potential structure refinement (EPSR) modeling was used to analyze the X-ray scattering data. Ca2+ forms a rigid coordination shell consisting of about seven water molecules at 2.48 Å and one NO3− at 25~170 °C, with further water molecules substituted by NO3− at 210 °C. NO3− is surrounded by 13~14 water molecules at an N–Ow distance of 3.6~3.7 Å. The tetrahedral network structure of solvent water pertains from 25 to 170 °C but is transformed to a dense packing arrangement at 210 °C.

Inelastic Scattering in Weak Localization for Single‐Layer Graphene

Chemical‐vapor‐deposited graphene is used extensively to fabricate devices. However, the charge‐neutral point (CNP) of this material appears at a relatively high back‐gate voltage (VG) because of molecular adsorption and impurities on the graphene surface. In this study, a Ti‐cleaning process is used to remove contaminants from the transferred graphene. Two contributions to the magnetoresistance are investigated: weak localization (WL) and inhomogeneous charge transport near the Dirac point. One of the most important parameters for clarifying the quantum transport properties is the inelastic scattering time. Fitting of the experimental results with a theoretical WL expression is performed to investigate the temperature and VG dependence of the inelastic scattering and intervalley scattering rates. Small momentum transfer due to Nyquist scattering is dominant in the CNP region, while large momentum transfer processes of direct electron–electron interaction dominate the electron and hole‐transport regions.

Iron redox effect on the structure and viscosity of a sodium silicate glass and melt

The viscosity of silicate melts is one of the most important physical properties for understanding high-temperature phenomena in magmatic systems and material processing. The effects of composition and temperature on viscosity have long been elucidated. Although iron ions are the main components of magmatic systems, their influence on viscosity remains unclear because the behavior of iron is complicated; iron ions have two redox states, Fe3+ and Fe2+. Here, we elucidate the viscosity of an iron-sodium-silicate system with a variety of iron redox states at temperatures close to its glass transition temperature (Tg). The redox states and structures of the samples were characterized using x-ray absorption near-edge structure (XANES) spectroscopy, Raman spectroscopy, synchrotron x-ray total scattering, and density (molar volume) measurements. The viscosity increased (by more than four orders of magnitude) with an increase in the ratio of Fe3+ to total Fe (Fe3+/Fetot), whereas the temperature dependence of the viscosity was larger for glasses with a higher Fe3+/Fetot ratio at temperatures close to the glass transition temperature. The tendencies in viscosity and structural variation against the Fe3+/Fetot ratio support the consensus on the structural roles of Fe3+ and Fe2+ from previous studies: Fe3+ ions have a stronger tendency to behave as network formers than Fe2+ ions.

Magnetic properties of the Y<sub>2</sub> (Fe<sub>x</sub>Co<sub>1-x</sub>)<sub>17</sub> compounds

The results of magnetization curves analysis of Y2(FexCo1−x)17 compounds, measured in 300—923 K temperature interval along easy and hard magnetization direction, were represented. Magnetocrystalline anisotropy constants K1,2 of the samples were calculated. Temperature and compositional dependence of anisotropy constants K1,2 and saturation magnetization Ms were discussed. There is an increase of first anisotropy constant K1 value with the increase of relative samples iron concentration with maximum value of 5.1∙105 J·m-3 in x = 0.29 point, correspond to the middle of the easy-axis interval.

Activation analysis of the temperature dependence of the dielectric constant of ferroelectrics

For ferroelectrics lead zirconate titanate and barium titanate, an exponential dependence of the dielectric constant on temperature is shown, provided that the Curie–Weiss law is satisfied. The temperature of equality of ferroelectric dielectric constants for activation processes caused by the interaction of domain walls with point defects, as well as the corresponding activation energies, have been determined.

Synthesis and Complex Dielectric Properties of Ba0.4Sr0.6SnO3 Ceramics with Thorn-like Microstructure.

In this study, we synthesized perovskite Ba0.4Sr0.6SnO3 ceramics with a unique thorn-like microstructure using the solid-state reaction method. The structural and complex dielectric properties were investigated in detail. X-ray diffraction was employed to characterize the phase purity, while X-ray photoelectron spectroscopy was used to analyze the chemical state of the components. The frequency and temperature dependence of the dielectric properties indicates that both the dielectric constant and loss are influenced by A-site ion doping as well as the presence of the thorn-like microstructure. The observed dielectric behavior can be explained by the interfacial polarization and dielectric relaxation processes, which arise from the existing Sn4+-Sn2+ pairs, oxygen vacancies, and defects with activation energies of 0.38 eV, 0.73 eV, and 0.54 eV, respectively. The resistances of grain boundaries, grains, and the thorn-like structure were revealed by the impedance spectra. These findings provide valuable insights into understanding structure-property relationships in perovskite stannate ceramics.

Investigation of Dislocations Introduced in Si Wafer during Flash Lamp Annealing by Photoluminescence Spectroscopy

Dislocations are generated in Si wafers during flash lamp annealing for 20 ms. The samples have been etched to different depths and macro‐photoluminescence (PL) spectra have been recorded for different dislocation densities. A micro‐PL investigation is also carried out on a cross section of a sample. Four characteristic emission peaks are found, which are the well‐known D1, D2, D3, and D4 lines. The findings demonstrate a significant influence of the defect densities on the PL spectra of the D lines by using both the micro‐ and the macro‐PL setups, and show a correlation of the PL intensities with etch pit density measured against the depth of the wafer. Additionally, the D lines dependency on temperature is explored, offering insights into the underlying mechanisms. The D lines exhibit a pronounced temperature dependence, which can be attributed to various factors including phonon interactions and thermal expansion effects. The influence of nickel contamination is also examined.

Ordered Aggregates of Fmoc-Diphenylalanine at Alkaline pH as a Precursor of Fibril Formation and Peptide Gelation.

The ultrashort peptide N-fluorenylmethoxycarbonyl-phenylalanyl-phenylalanine (FmocFF) has been largely investigated due to its ability to self-assemble into fibrils (100 nm-μm scale) that can form a sample-spanning gel network. The initiation of the gelation process requires either a solvent switch (water added to dimethyl sulfoxide) or a pH-switch (alkaline to neutral) protocol, both of which ensure the solubility of the peptide as a necessary step preceding gelation. While the respective gel phases are well understood in structural and material characteristics terms the pregelation conditions are known to a lesser extent. The question we asked is to what extent the gel-forming fibrils are already partially formed, i.e., oligomers or protofibrils. Focusing on the pregelation conditions for the pH-switch method, we investigated the self-assembly of soluble FmocFF aggregates in alkaline pH by UV circular dichroism, IR, vibrational circular dichroism, and 1H NMR spectroscopy for different peptide concentrations and more systematically as a function of temperature. The temperature dependence of the UVCD spectra of FmocFF in H2O and D2O revealed a complicated isotope effect that affects the peptide backbone and fluorene conformations in peptide aggregates differently. Moreover, we found that the melting of formed aggregates depends on peptide concentration in a nonmonotonic way. At 20 mM the UVCD data revealed the population of at least two different thermodynamic intermediate states, which seem to differ in terms of the relative arrangement of the fluorene moiety. The IR spectrum of this sample at room temperature indicates an antiparallel β-sheet arrangement, as suggested earlier in the literature. However, we show that this interpretation can only be valid if one invokes a nondispersive redshift of the two amide I' bands in a locally crystalline environment. The respective vibrational circular dichroism spectrum of the amide I' region is consistent with a left-handed helically twisted structure of the formed aggregates. A comparison of our data with spectra of the aqueous gel phase suggests that fibrils in the latter resemble the ones at alkaline pH probed by our experiments.

Influence of Operating Temperature on Crack Growth Characteristics and Fatigue Life Prediction of Carbon Black-Filled Hydrogenated Nitrile Butadiene Rubber.

Rubber is widely used in situations involving cyclic loads, and the influence of temperature on rubber properties is particularly pronounced under cyclic loading. In this study, mechanical property tests and crack propagation tests of carbon black-filled hydrogenated nitrile butadiene rubber were conducted at four different operating temperatures. Based on the results of the crack propagation tests, the temperature-dependent characteristics of the Paris-Erdogan parameters and strain energy density were clarified. The Paris-Erdogan parameters were successfully expressed as a function of temperature. The strain energy density, on the other hand, exhibited the property of being strongly influenced by factors of strain, loading frequency, and others, while the temperature dependence was weak. On this basis, the unified fatigue crack growth kinetic model was constructed at multiple temperatures. The model results can match the experimental data well, particularly at temperatures of 60 °C and 80 °C. Finally, the fatigue life prediction model at different temperatures was constructed by combining the fatigue life test results. The results indicate a correlation between crack propagation characteristics and fatigue life predictions across different operating temperatures, with the predictions agreeing well with the measured life. The models can be used to analyze early fracture behavior or fatigue life prediction of rubber at different operating temperatures and minimize the need for extensive product testing prior to the manufacture of rubber products.

Temperature Areas of Local Inelasticity in Polyoxymethylene.

The spectra of internal friction and temperature dependencies of the frequency of a free-damped oscillation process excited in the specimens of an amorphous-crystalline copolymer of polyoxymethylene with the co-monomer trioxane (POM-C) with a degree of crystallinity ~60% in the temperature range from -150 °C to +170 °C has been studied. It has been established that the spectra of internal friction show five local dissipative processes of varying intensity, manifested in different temperature ranges of the spectrum. An anomalous decrease in the frequency of the oscillatory process was detected in the temperature ranges where the most intense dissipative losses appear on the spectrum of internal friction. Based on phenomenological model representations of a standard linear solid, the physical-mechanical (shear modulus defect, temperature position of local regions of inelasticity) and physical-chemical (activation energy, discrete relaxation time, intensities of detected dissipative processes) characteristics of each local dissipative process were calculated. It was found that the intensities of dissipative processes remain virtually unchanged for both annealed and non-annealed samples. The maximum variation in the shear modulus defect is 0.06%. Additionally, according to computational data, small changes are also characteristic of the following parameters: the activation energy varies from 0.5 to 1.4 kJ/mol and the relaxation time changes from 0.002 to 0.007 s, depending on the presence or absence of annealing. As a result of annealing, there is a significant increase in the relaxation microinheterogenity of the polymer system across the entire temperature range (250% for the low-temperature region and 115% for the high-temperature region).

Interplay of chain dynamics and ion transport on mechanical behavior and conductivity in ionogels.

Understanding the interplay among the mechanical behavior, ionic conductivity and chain dynamics of ionogels is essential for designing flexible conductors that exhibit both high conductivity and excellent mechanical properties. In this study, ionogels were synthesized via the radical polymerization of N,N'-dimethylacrylamide (DMAA) and methacrylic acid (MAAc) monomers in the presence of ionic liquid 1-ethyl-3-methylimidazolium trifluoromethane sulfonate ([EMIM][OTf]). By varying the mass content of ionic liquid within ionogels, we investigated the mechanical behavior and ionic conductivity at the macroscopic scale using tensile, rheological testing and electrochemical impedance spectroscopy, as well as the dynamic behavior of chain segments and ions within the network at the microscopic scale using broadband dielectric relaxation spectroscopy (BDS) over a broad temperature range. Our findings revealed that variations in ionic liquid concentration significantly affect mechanical performance, ionic conductivity, complex conductivity spectra, and complex permittivity spectra. These ionogels exhibited remarkable stretchability, adhesion, and strain-sensing capabilities. Analysis of BDS indicated that the temperature dependence of the hopping frequency (ωH), the conductivity of free ions (σdc), and the relaxation time (τs) of chain segments conforms to the Vogel-Tammann-Fulcher (VTF) equation for ionogels with varying ionic liquid content. By correlating τs measured through rheological tests and BDS, we observed a transition from Arrhenius to VTF behavior, which shifts towards lower temperatures with increasing ionic liquid content. This study highlighted a strong coupling between σdc and ωH, as well as between 1/τs and ωH, at low ionic concentrations, facilitating high mechanical performance of the ionogels due to viscoelastic energy dissipation. However, as the ionic concentration increased, a slight decoupling of σdc and ωH was noted, leading to a substantial reduction in the mechanical properties of the ionogels. Ultimately, these ionogels demonstrate potential as polymer electrolytes for applications in flexible wearable devices.

SCREENING OF MARINE SPORE-FORMING BACTERIA DEGRADING POLYMER MATERIALS

The development of plastic recycling methods requires the search for new microorganisms capable of their biodegradation. The aim of the work was to screen spore-forming bacteria isolated from bottom sediments of the Black Sea for their ability to decompose Impranil and polyethylene terephthalate. Materials and methods. Cultivation of sixty cultures of spore-forming bacteria isolated from the Black Sea was carried out on a solid LB medium supplemented with Impranil (3–4 ml/l) or bis(hydroxyethyl)terephthalate (BHET) (5 mM). The ability of cultures to decompose polymer additives was evaluated by the formation of a transparent zone around the colonies after incubation at 30 ºС and 37 ºС for 14 days. Results. Out of 60 strains, 40 showed a positive result. 22 strains were active towards both plastics, 13 – only towards Impranil, 5 – only BHET. Impranil was decomposed somewhat more actively at 30 °C than at 37 °C. No clear temperature dependence was found in BHET decomposition. The analysis of the species composition showed that 35 of the 40 active strains belonged to seven species of microorganisms. B. subtilis has the highest share of active strains, as this species is represented by 13 strains, each of which was found to be active. The most active strain belonged to the species B. reuszeri. Conclusions. Spore-forming bacteria isolated from the Black Sea are capable of degrading Impranil and BHET. Enzymes degrading above mentioned polymers are the most widespread among the representatives of the species B. subtilis, B. atrophaeus and B. reuszeri. The highest activity towards Impranil showed B. subtilis, towards BHET– P. megaterium, B. reuszeri and B. licheniformis. Impranil degradation was more active under 30 ºС, but no clear dependence between temperature and BHET degradation was detected.

Enhancing Rashba Spin-Splitting Strength by Orbital Hybridization.

A Rashba spin-splitting state with spin-momentum locking enables the charge-spin interconversion known as the Rashba effect, induced by the interplay of inversion symmetry breaking (ISB) and spin-orbit coupling (SOC). Enhancing spin-splitting strength is promising to achieve high spin-orbit torque (SOT) efficiency for low-power-consumption spintronic devices. However, the energy scale of natural ISB at the interface is relatively small, leading to the weak Rashba effect. In this work, we report that orbital hybridization inducing additional asymmetry potential at the interface observably enhances spin-splitting strength, verified in the hexagonal boron nitride (h-BN)/Co3Pt heterostructures. First-principles calculations suggest the sizable Rashba spin-splitting derived from the out-of-plane p-d hybridization combined with SOC at the h-BN/Co3Pt interface. Then, the SOT efficiency is observably enhanced via the Rashba effect at the h-BN/Co3Pt interface and exhibits unusual temperature dependence, in which the large-area h-BN is in situ grown on the Co3Pt layer with perpendicular magnetic anisotropy by magnetron sputtering. Especially, the dominant damping-like torque is observed, resulting in the lower threshold switching current density and the enhanced switching ratio. Our results provide opportunities for interfacial control to enhance the Rashba effect and the SOT efficiency in heterostructures. It is expected to contribute to the design of energy-efficient spintronic devices.