Temperature Tc Research Articles

Comparative optimization of the thermal performance for H2 – Metal hydride heat storage and heat pump systems

Metal hydride is very promising in hydrogen storage and simultaneously the thermal effect in the reversible hydrogenation process makes it possible in heat storage and heat pump area. The interaction of H2 – Metal – hydride pair and its further applications need comprehensive thermodynamic design and performance optimization. Therefore, this work makes thermodynamic comparative research of heat storage and heat pump systems by adopting H2 – Metal-hydride pair. According to the investigation, the thermodynamically optimal charging-discharging temperatures (Tm1,Tm2), the heat source temperature (Th1) and the ambient temperature (Tc1) meet the relationship of Tm1Tm2=Th1Tc1 for the heat storage system. Given the operating pressure (p), there exists a well-matched temperature (T) range to maximize the exergy performance of metal hydride heat storage system. Meanwhile, the running p-T is positively correlated, e.g., when the charging pressure is set at 0.2 MPa to 0.3 MPa, the well-matched T varies from 307 K to 317 K. When the discharging pressure is set at 0.4 MPa to 0.7 MPa, the well-matched T varies from 304 K to 320 K. For the metal hydride heat pump system, the optimal performance lies in maximizing the transported heat. Given the operating T, there exists a well-matched pressure range for the heat sink device, e.g., for the heat releasing process, when operating T is set at 353 K, 363 K, 373 K, 383 K and 393 K, the well-matched p are 2.3 MPa, 3.3 MPa, 3.8 MPa, 4.6 MPa and 6.1 MPa. Both the heat storage and heat pump performances are also affected by the operating pressure – temperature −transported heat, presenting improved region and degraded region. The optimal thermodynamic criterion and the matchability of the operating parameters provide a theoretical guidance for the MH-based thermodynamic system design and operation.

From weak- to strong-coupling superconductivity in the AlB2-type solid solution SrGa1−xAlxGe with honeycomb layers

We report on the structure and the superconducting properties of 9-electron 111 compounds with honeycomb layers, namely SrGaGe, SrAlGe, and the SrGa1-xAlxGe solid solution. By means of single-crystal x-ray diffraction we show that, on one hand, SrGaGe crystallizes into the centrosymmetricP6/mmmspace group (a= 4.2555(2) Å,c= 4.7288(2) Å) with statistical disorder in the [GaGe]62-honeycomb layers. On the other hand, we confirm that SrAlGe crystallizes in a non-centrosymmetric space group, namelyP6¯m2(a= 4.2942(1) Å,c= 4.7200(2) Å) with fully ordered [AlGe]62-honeycomb layers. By using magnetization and specific heat measurements, we show that the superconducting properties of SrGaGe and SrAlGe differ significantly from each other. SrGaGe is a superconductor with a critical temperature ofTc= 2.6 K falling into the weak coupling limit, while SrAlGe has aTc= 6.7 K and can be classified in the strong coupling limit. By realizing the SrGa1-xAlxGe solid solution, we were able to investigate the transition between the different crystal structures as well as the evolution of the electronic properties. We show that the transition from the weak-to strong-coupling superconductivity in this system is likely associated with the disorder-to-order transition of the honeycomb layer, along with the loss of the inversion center in the crystal structure.

Structural, magnetic and dielectric properties in double perovskite La2-xScxCoMnO6 (x = 0.0, 0.1, and 0.2)

The effect of Sc doping on structural, magnetic, and dielectric properties of double perovskite La2CoMnO6 synthesized by solid-state method was investigated. Crystal structure of La2-xScxCoMnO6 (x = 0.0, 0.1, and 0.2) compounds confirmed through X-ray diffraction patterns (XRD). Rietveld refinement of the XRD revealed the monoclinic phase with P21/n space group and the structural properties such as lattice parameter, bond lengths, and bond angles were obtained. Field emission scanning electron microscopy images revealed a uniform grain distribution, and the grain size was increased with increasing Sc content. The elemental mapping confirms the stoichiometry of the compounds. The room temperature Raman spectra confirm the monoclinic crystal structure and reveal two broad peaks viz., Ag, and Bg which were attributed to specific vibrational modes within the (Co/Mn)O6 octahedra. Magnetic measurements show that Curie temperature (Tc1) decreases with Sc substitution of 206 K for x = 0.0–193 for x = 0.2 due to the Co2+-Mn4+ FM coupling and it follows Curie–Weiss law in the paramagnetic region. Impedance spectroscopy studies show that the conductivity in these materials is predominantly due to the intrinsic bulk grains.

Determination of the coefficient of thermal effusivity ε for a semi-confined rod

The article provides methods and formulas for calculating the coefficient of thermal effusivity ε (coefficient of heat accumulation) of solid bodies using known solutions of direct heat conduction problem. The work describes a method by which the final formulas are simplified to algebraic equations using the relative temperature θM of heating semi-confined rod from the end. The temperature Tc at the beginning of the rod is measured — x0 and time — τ0 from the start of heating. For calculation, the amount of heat Q accumulated during heating by a heater with a constant temperature at the end of the rod is used for the entire heating time. The technique is physically implemented during the experiment by bringing the ends of two semi-confined rods into contact. A flat, low-inertia electric heater is placed between the rods. The amount of heat ∆Q used in the calculations is half of the total heat of the heater for the entire heating time.

Study of magnetic phase transitions by helium-3 in DyF3 nanoparticles

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.7 %) and DyF3 (0.3 %) powders at temperatures of 1.5–3 K was studied by pulsed nuclear magnetic resonance. DyF3 particles have ellipsoidal shape and average size 225 × 153 nm with the magnetic phase transition at temperature Tc = 2.45 K. The temperature dependence of the longitudinal and transverse magnetization relaxation rates of 3He nuclei with a mixture of LaF3 and DyF3 powders has a broad maximum near Tc, which is related to the magnetic phase transition. It is shown that the adsorbed layer of 3He is extremely sensitive to magnetic phase transitions. Preplating the particles surface with adsorbed nitrogen layers allowed to vary the distance from 3He nuclei to the surface of particles in a controlled way. Calculations of the nuclear magnetic relaxation rates with a change in the distance of helium-3 from the particle surface have been carried out, which is in good agreement with experimental data. It was shown that helium-3 is extremely sensitive to surface magnetism and can be used to study surface effects and surface magnetism.

Effects of Fe substitution for Mn on structural, magnetic and magnetocaloric properties of TbMn2-xFexSi2

The structural and magnetic properties of TbMn2-xFexSi2 compounds (x = 0.0–0.4) have been investigated in details by high-resolution synchrotron x-ray and neutron powder diffraction, specific heat, and dc magnetization measurements. The replacement of Fe for Mn in TbMn2-xFexSi2 does not change the crystal structure but leads to a significant contraction of the unit cell (dV/dx ∼ - 6 Å3) and modification of three magnetic phase transition temperatures – the Curie temperatures Tc1, Tc2 and the Néel temperature TN. For example, the Tc1, Tc2 and TN values of TbMn2Si2 decrease from Tc1 = 50 K, Tc2 = 64 K and TN = 500 K to Tc1 = 27 K, Tc2 = 37 K and TN = 440 K for TbMn1.6Fe0.4Si2. Detailed neutron diffraction investigations have allowed us to determine the magnetic structures and construct the magnetic phase diagram as well as confirm the presence of magnetoelastic coupling effects. The significantly different responses of Tc1 and Tc2 to applied magnetic fields (e.g. dTc1/dB = 0.52 K/T and dTc2/dB = 4.7 K/T for TbMn1.6Fe0.4Si2), leads to expansion of the temperature region (ΔT = Tc2- Tc1) for the canted ferromagnetic state Fmc-ii between Tc1 and Tc2. In the case of TbMn1.6Fe0.4Si2, ΔT increases from ΔT = 9 K for applied magnetic field B = 0.2 T to ΔT = 36 K for B = 6 T, resulting in plateau-like behaviour of magnetic entropy change and enhances the relative cooling power (RCP) in this system. Under a change of magnetic field of 0 T – 5 T, the maximum value of the magnetic entropy changes -ΔSmax and adiabatic temperature change, ΔTad are derived to be -ΔSmax = 13.1 J/kg K and ΔTad = 8.4 K with the RCP = 411 J/kg for x=0.4 sample. The plateau-like magnetocaloric effect and relatively large RCP make these materials potentially suitable for application in cryogenic magnetic refrigeration.

Design, synthesis and Characterization of a novel antiferroelectric solid solution (1-x)PbHfO3-xBiAlO3

Antiferroelectric (AFE) materials are potentially useful for energy storage applications. Lead hafnate (PbHfO3) is one of the prototypical AFE materials. However, its critical field (Ecr) which is needed to induce the AFE to ferroelectric phase transition is close to the dielectric breakdown strength. To reduce Ecr, we prepare the solid solutions of (1-x)PbHfO3–xBiAlO3 (x = 0.00–0.04) via solid state synthesis. The crystal structures, dielectric behaviour, ferroelectric properties, and energy storage properties are investigated. A temperature-composition phase diagram is established. At room temperature, the crystal symmetry of all compositions is orthorhombic with the Pbam space group. Upon heating, the transition to the AFE orthorhombic Imma phase is observed at the temperature TC1, which slightly decreases with increasing x, followed by the transition to the cubic phase at the temperature TC2, which does not depend on x. Distinct dielectric anomalies are observed at TC1 and TC2. It is found that BiAlO3 substitution reduces Ecr and the polarization–electric field relations display characteristic double hysteresis loops. For x = 0.04, at a comparatively small applied field of 130 kV/cm, the values of recoverable energy density (Wrec) and efficiency of 0.24 J/cm3 and 84 %, respectively, are obtained. At 190 °C, a Wrec = 0.75 J/cm3 and a very high efficiency of 92 % are obtained at the field of 50 kV/cm. Thus, the prepared material can potentially be used in high-temperature pulsed power capacitors for energy storage applications within the temperature range from room temperature up to 190 °C.

Entropy optimization of lid-driven micropolar hybrid nanofluid flow in a partially porous hexagonal-shaped cavity with relevance to energy efficient storage processes

Hydromagnetically associated heat convection can greatly enhance the performance of high-efficiency thermal appliances and renewable energy sources through an optimized design. This investigation examines the production of thermodynamic irreversibility and heat convection for a double lid-driven flow within a partially porous stratified hexagonal enclosure. The top and bottom-wall are moving in the opposite direction with an equal velocity U0. The top-wall and the bottom-wall are kept at temperature Tc and Th (Th >\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$>$$\\end{document} Tc) while the slanted walls are assumed to be thermally insulated. A constant magnetic field is employed in the horizontal x-direction. The hexagonal cavity was filled with a micropolar hybrid nanofluid Ag-MgO/water. The system of dimensionless equations was solved by the finite difference method (FDM) associated with successive over-relaxation (SOR), successive under-relaxation (SUR), and Gauss–Seidel iteration tactics and required results are computed with problem specific program in MATLAB code. The results indicate that the Ra and the thickness of the porous layer (Xp) significantly influences heat convection and thermal irreversibility processes. The Nuavg and STotal rises 6.299% and 3.373% as ‘ϕhnf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upphi }_{{\ ext{hnf}}}$$\\end{document}’ enhances from 0 to 4%, respectively. Furthermore, as the values of Ra, Ha, K0, and ϕhnf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upphi }_{{\ ext{hnf}}}$$\\end{document} increase, Beavg experiences a decline of 53.73%, 11.04%, 38.36%, and 0.09% respectively. Also, movement of wall has a significant impact on heat transfer rates and entropy production. The present study may be extended in numerous areas to mimic the problems like—(1) onset of thermo-mechanical process for solid–fluid interaction in a conduit. (2) Thermos-chemical process with extraction of ions in two-phase fluid for double layer plating on a continuously moving sheet, as region of porous stratum saturated with a class of fluid and region without porous medium occupied with other fluid.

Influence of Complex Plasticizer on Plasticizing Effects and Rheological Properties of Plasticized Poly(Vinyl Alcohol)

AbstractPoly(vinyl alcohol) (PVA) was modified using D‐mannitol (DM) and 1‐butyl‐3‐methylimidazole bromide (BMIMBr) as the complex plasticizer (DB), and PVA/DB composite was prepared. The plasticizing effect of DB on PVA was studied by Fourier transform infrared spectroscopy (FT‐IR), differntial scanning calorimetry (DSC), thermos gravimetric analysis (TGA) and melt flow indexer (MI). FT‐IR analysis indicated that Br− of BMIMBr and OH of DM could form H‐bonds with OH of PVA. With the increase of DB, the melt temperature (Tm2) and crystallization temperature (Tc1) of PVA/DB composite decreased, the initial thermal decomposition temperatures (Td), thermal processing window (ΔT) and MI values increased respectively. Based on above studies, the influence of DB content on rheological properties of PVA/DB composite was investigated by the capillary rheometer. The result displayed that apparent viscosity of PVA/DB composite decreased with increasing DB content, shear rate and measured temperature. The non‐Newtonian index (n) increased and structural viscosity index (Δη) decreased with the increase of measured temperature and DB. The viscous flow activation energy (Eη) decreased as the shear rate and DB content increased. When the measured temperature, DB content and shear rate were in the range of Tm2+30 −Tm2+35 °C, 40–50 wt% and 764.8–1504.9 s−1, respectively, the spinnability of PVA/DB composite was optimal, which will lay a theoretical foundation for the exploration of melt spinning process in the future.

Magnon dispersion, magnetization, and thermodynamic properties of 2D-Sc/GaAs diluted magnetic semiconductor (DMS)

In this paper, the effect of magnon scattering, light–matter coupling strength, temperature, and applied dc field H0 on magnon dispersion, density of magnons, magnetization, and thermodynamic properties of 2D-Sc/GaAs DMS material is studied. The Green function formalism is used to find the magnon dispersion and density in single-mode excitation employing the quantum field theory. Our findings indicate that ferromagnetic phase change is obtained within a limited low-temperature range based on the product Ω0T5/2, which remains below unity and varies with the amount of magnon scattering factor Ω0. It was presumed that the density of localized magnetic impurities can be controlled by taking into account the numerical stability with the number of holes required for mediation, and therefore, a scandium (Sc) dopant and its kind, which have a double functionality of creating holes and adding magnetic impurities from their 3d suborbital, are the best choice to replace those with higher spin magnetic moments. We also observe that the magnetic curves broaden as the temperature further rises and decrease with the enhancement of the magnon scattering factor, perhaps, due to quenching of fermionic spins ceasing the interband excitation. However, in the absence of this factor, the magnetization decreases linearly with the increase in the temperature, breaking the Bloch T3/2 low, perhaps, introducing anomalous condition to such 2D materials. The light–matter coupling strength and the dc field H0 are alleged to be responsible for the formation of the energy gap and variation of magnon dispersion. This work suggests that there is a point above which the temperature TC may not rise with the increase in the impurity concentration x due to magnon scattering, distressing the entire thermodynamic property.

THERMAL SOURCE EFFECT ON THE NATURAL CONVECTION OF A NANOFLUID WITHIN A TRIANGULAR CAVITY

Natural convection is numerically studied in a triangular cavity whose inclined walls that is isothermal at temperature TC, while its base is thermally insulated. The cavity contains a hot isothermal cylindrical heat source TH of diameter D. In this study, we used the nanofluid (water + TiO2). The nanoparticle volume fraction is varied within the range 0.01 ≤ ϕ ≤ 0.05, and the Rayleigh number is set between 103 and 106. The main objective of this study is to explore the impact of nanoparticle concentration, Rayleigh number (Ra), and heat source position (h) on the enhancement of convective thermal transfer. The simulation results show that thermal exchange improves with increasing Ra, heat source diameter, and nanoparticle volume fraction (ϕ).

“Metallization” of semimetals by an external electric field

The paper considers the possibility of changing the energy spectrum of the electronic subsystem of semimetals from a non-degenerate to a degenerate state under the action of an external electric field. This “metallization” of semimetals is achieved by increasing the concentration of free electrons in the external field. The work also considers the possible transition of “metallized” semimetals to the superconducting state. The evaluations made show that for the size of the sample R ≤ 100 nm and for the magnitude of the field source voltage U ≈ 10 V, “metallized” semimetals and their solid solutions can undergo transition to a superconducting state at temperatures Tc ≥ 100 K, which is an order of magnitude higher than the characteristic temperature value Tc for classic metals.

Structure, Microstructure, and Dielectric Properties of Bi<sub>0.5</sub>(Na<sub>0.78</sub>K<sub>0.22</sub>)<sub>0.5</sub>TiO<sub>3 </sub>Lead-Free Ceramic

In this article, the structural, microstructural, and dielectric properties of Lead- free perovskite ceramic Bi0.5(Na0.78K0.22)0.5TiO3 [BNKT] have been reported. The material was synthesized through the solid-state reaction method. The compound formed is found to have a hexagonal structure, confirmed by XRD analysis of the sample. The microstructural analysis of the compound revealed the polycrystalline nature of the ceramic having quasi-cubic grain morphology with distinct grain boundaries. From the dielectric study, it was found that the dielectric constant increases with temperature and attained maximum value at temperature Tc = 335° C, after which it decreased. The frequency independence of transition temperature (Tc) suggested the classic ferroelectric behaviour of the compound. The broad dielectric peak around transition temperature confirms the relaxor behaviour of the compound as well as diffused phase transition at Tc. The value of the relative permittivity and loss tangent at ambient temperature for 1kHz frequency is 627 and 0.223 respectively. The synthesized material can be utilized for the fabrication of capacitors and energy storage applications.

Unconventional superconductivity in PdxBi2Se3 whiskers

Studies of temperature dependence of magnetoresistance for PdxBi2Se3 whiskers in the temperature range 1.6-77K in magnetic field up to 10 T were carried out. Crystals were grown by chemical transport reaction method in closed bromide system. The source and crystallization zone temperatures were 1100 K and 780 K, respectively. Doping of the crystals was carried out during the growth process with palladium impurity to concentrations of (1 – 2) × 1019 cm−3. In the low-temperature region beginning at a temperature of 5 K and reaching a temperature 3.5 K, a sharp decrease in resistance was observed, which is associated with the transition to superconducting state. Based on the analysis of the temperature dependence of the resistance at fixed magnetic fields, the Curie temperature Tc1=5.3 K and Tc2=3.5 K as well as the upper critical magnetic field Bc2=1.45 T and 0.25 T were determined. The established parameters indicates in II type supercondor. This is indicated by the ratio Δ0/kBTc = 2.0, which exceeds BCS limit of 1.76 and indicates a relatively large value of the superconducting gap Δ0=0.8 meV. The determined ratio A/γ2, which establishes the relationship between the electron-electron and electron-phonon interaction, is about of 2ao, which indicates a strong fermionic interaction with phonons in the PdxBi2Se3 superconductor. The estimated value of the ratio of the Curie temperature to the effective Fermi temperature equal to 0.04 also falls within the range of 0.01 ⩽ Tc/TF ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.

Measurement of temperature flow analysis by condition monitoring system for WTG gear box to evaluate the thermal performance associated with plant load factor

This research work is mainly focused on the performance of the wind turbine power plant. The performance of the plant will depends on the working of wind turbine gearbox. Hence the parameters taken like inlet velocity of air, inlet temperatures and inlet pressure of the air entering into the gearbox. For experimentation a three stage gearbox has been considered and the data has been recorded for the period of 5 months. These results has been recorded with the help of SCADA software and the results are imported from SCADA for analyzing the minimum and maximum oil temperatures. Since these parameters effects directly on the thermal performance of the wind turbine power plant. From the analysis it was found that the temperature sensors for monitoring the oil TM1 and TM2 within temperature limits of 250οC and also the TS1 and TS2 Promises the sensing capacity within temperature limits up to 200 οC and response time is 30 minutes, also the coupling temperatures TC1 and TC2 gives very promising results upto 150 οC for 30 minutes response time.

Superconducting properties of van der Waals metal-rich subsulfide Nb1.7Ta3.3S2

Layered metal-rich subsulfides have become a promising area for exploring intriguing properties such as superconductivity, nontrivial topology, and charge density waves; however, despite their extraordinary potential, they have remained largely unexplored. We report a comprehensive analysis of a van der Waals layered metal-rich subsulfide, Nb1.7Ta3.3S2, using a range of measurement techniques, including AC transport, magnetization, and specific heat. Our measurements confirm the occurrence of a type-II superconducting transition at a temperature Tc = 3.64(2) K. Furthermore, specific heat measurements suggest weakly coupled nodeless superconductivity in Nb1.7Ta3.3S2.

Crystal Structure and Ferromagnetism of the CeFe9Si4Intermetallic Compound

We have determined the crystal structure and the magnetic state of the CeFe9Si4 intermetallic compound. Our revised structural model (fully ordered tetragonal unit cell, I4/mcm) agrees with the previous literature report, except for some minor quantitative differences. Magnetically, the CeFe9Si4 undergoes a ferromagnetic transition at the temperature TC ≈ 94 K. Ferromagnetism in the combined Ce-Fe spin system is a result of interplay between the localized magnetism of the Ce sublattice and the Fe band (itinerant) magnetism. Ferromagnetic ordering obeys the rather general rule that the exchange spin coupling between atoms possessing more than half-full d shells with atoms possessing less than half-full d shells is antiferromagnetic (where the Ce atoms are considered as light d elements). Since in rare-earth metals from the light half of the lanthanide series, the magnetic moment is directed opposite to the spin, this results in ferromagnetism. The magnetoresistance and the magnetic specific heat show an additional temperature-dependent feature (a shoulder) deep inside the ferromagnetic phase that is considered to originate from the influence of the magnetization on the electronic band structure via the magnetoelastic coupling, which alters the Fe band magnetism below TC. The ferromagnetic phase of CeFe9Si4 is magnetically soft.

Preparation and photoluminescence properties of Eu3+ doped Li2O–Al2O3–B2O3 glass-ceramics

Promising red emitting Li–Al–B glass (G) and glass-ceramics (GC) Eu3+ doped were prepared with composition 50–0.5xLi2O ·5–0.05xAl2O3·45–0.45xB2O3·xEu2O3 (x = 0, 0.5, 1.0 and 1.5 mol %). Different temperatures (Tg, Tx, Tc1, Tc2, Tm1 and Tm2) were obtained by Simultaneous DTA-TGA (SDT) measurements, obtaining a low on-set temperature, Tx, around 520 °C. LiAlB2O5 and LiBO2 are obtained as crystalline phases, but a new phase, Li3AlB2O6, emerges as Eu3+ increases, resulting in severely decreasing of crystallinity percentage of the GC system. Crystalline phases are identified through X-Ray Diffraction (XRD) and percentage of the amorphous phase is calculated. The Infrared and Raman spectra supports the evidence obtained in XRD measurements. Scanning Electron Microscopy shows different sizes and shapes of particles. Excitation and emission spectra, PLE and PL, respectively, were obtained, as well as time decay and quantum yield around 7.3%. Thermal behavior is analyzed for glass and glass-ceramics through thermal quenching and activation energy. A high thermal stability for GC is obtained with a thermal quenching (TQ1/2) higher than 250 °C, while TQ1/2 is 175 °C for G system. Red emitting color is calculated in the CIE diagram and is supported by visual evidence. The evidence of a distorted europium site in the different crystalline phases suggest the cause of the loss of crystallinity in glass-ceramics systems.

Description of a glass transition with immeasurable structural relaxation time

A general problem of studying supercooled liquids and glasses is very long relaxation times that do not allow determining explicitly dynamic characteristics. One of the ways to solve this problem is extrapolating values of some dynamical property (e.g. viscosity) from the temperature range where it can be directly measured (simulated) to the low-temperature region. Such extrapolations are usually contradictory because different fitting functions can give substantially different results. Thus, the development of methods for robust extrapolation is an urgent task especially for molecular dynamic study of glassforming liquids. Here we propose a model-free statistical algorithm for a low-temperature extrapolation of liquid viscosity (diffusion coefficient) and apply it to the problem of determination of glass transition temperature and the temperature Tc where the viscosity formally diverges. Our approach is based on numerical analytical continuation of temperature dependence of the viscosity using Padé approximants and error correction procedures using statistical averaging for the treatment of noisy input data. We tested the method on several glass-forming systems and revealed good stability and predictability. Our extrapolation algorithm is suitable for both numerical and experimental studies of glassformers when it is necessary to descend into the parameter range where structural relaxation times of a liquid are too long to be directly obtained.

Thermochromic properties of vanadium oxide thin films prepared by reactive magnetron sputtering at different oxygen concentrations

Vanadium dioxide (VO2) is a thermochromic (TC) material, exhibits a reversible transmittance change in the near-infrared (NIR) region upon heating above a critical temperature τc, due to an insulator-to-metal phase transition. Numerous studies on the V–O system can be found in the literature, including the synthesis of VO2 films. The phase diagram of the V–O system involves complicated suboxide phases that prevent pure VO2 formation and obscures quantitative analysis. Here, VO2 thin films were systematically prepared with various oxygen flow ratios (Γ) using reactive magnetron sputtering. Thin films prepared with Γ = 4.1% show dominant VO2 phase and the highest TC performance. The Γ-range producing dominant VO2 phase is found to be narrow: 3.7% < Г<4.2%. At lower and higher Γ, TC characteristics are shown to be accompanied, as expected, by electrical conductivity changes, but also by microstructure transformations. The latter producing textured films that gradually develop upon cycling around τc. In particular, a change of texture, yielding oriented VO2 crystallites, is observed by in-situ XRD around τc. Our results shed light on the VO2 formation and associated structural, chemical and electrical properties under various oxidizing conditions during magnetron sputtering, which calls for careful preparation and strategies to stabilize the VO2 phase.