Large Temperature Range Research Articles

Laser heating of ferroelectric cubes for tunable electromagnetic properties in metamaterials

In this experimental study, we demonstrate the feasibility of a thermally tunable, resonant dielectric microwave metasurface based on sub-wavelength Mie resonances of ferroelectric dielectric cubes (Calcium titanate, CaTiO3) in which the temperature of the meta-atoms can be locally and dynamically controlled by heating with an optical laser beam over a large range of temperatures and, consequently, values of the dielectric constant of the cube and corresponding resonance frequency of the meta-atoms. This avoids any interference of otherwise necessary heating elements or power supply wires with the propagation of the microwave signal and can be made spatially addressable. The concept scales at least to the THz domain. This contactless approach opens up an alternative avenue to tunability and active control of metamaterials.

Improved Bipolar Properties of Ester-Functionalized Discotic Diimine-Dithiolene Complexes.

A series of platinum diimine-dithiolene complexes with a 5,6-dihydro-1,4-dithiin-2,3-dithiolato (dddt2- ) dithiolene ligand and a bipyridine carrying tris-alkoxyphenyl fragments connected through an ester linker (bpyCn, n=8, 12, 16, 10(s), 20) (Scheme 1) has been developed. The mesomorphic properties of the ligands and of the platinum complexes have been investigated by a combination of DSC, POM and SAXS analyses. The platinum complexes were found to self-organize into columnar mesophases of hexagonal symmetry over large temperature range including room temperature. Their electronic properties were also characterized by a combination of electrochemistry, absorption and emission spectroscopy measurements and TD-DFT calculations. Besides being liquid crystalline, these compounds can undergo two oxidation processes and two reduction processes in a fully reversible manner, allowing the isolation of stable dicationic and dianionic species. Such a behavior is highly promising for the development of ambipolar semiconducting soft materials.

Modulated Kondo screening along magnetic mirror twin boundaries in monolayer MoS2

When a single electron is confined to an impurity state in a metal, a many-body resonance emerges at the Fermi energy if the electron bath screens the impurity’s magnetic moment. This is the Kondo effect, originally introduced to explain the abnormal resistivity behaviour in bulk magnetic alloys, and it has been realized in many quantum systems over the past decades, ranging from heavy-fermion lattices down to adsorbed single atoms. Here we describe a Kondo system that allows us to experimentally resolve the spectral function consisting of impurity levels and a Kondo resonance in a large Kondo temperature range, as well as their spatial modulation. Our approach is based on a discrete half-filled quantum confined state within a MoS2 grain boundary, which—in conjunction with numerical renormalization group calculations—enables us to test the predictive power of the Anderson model that is the basis of the microscopic understanding of Kondo physics.

A perspective on high‐temperature heat storage using liquid metal as heat transfer fluid

AbstractEnergy storage systems are essential to secure a reliable electricity and heat supply in an energy system with high shares of fluctuating renewable energy sources. Thermal energy storage systems offer the possibility to store energy in the form of heat relatively simply and at low cost. In concentrating solar power systems, for instance, molten salt‐based thermal storage systems already enable a 24/7 electricity generation. The use of liquid metals as heat transfer fluids in thermal energy storage systems enables high heat transfer rates and a large operating temperature range (100°C to >700°C, depending on the liquid metal). Hence, different heat storage solutions have been proposed in the literature, which are summarized in this perspective. Based on these, future technical advances are suggested such as reducing the liquid metal share in the heat storage, using waste material as storage medium or using liquid metal as heat transfer fluids not only in sensible, but in latent or thermochemical energy storage systems. The use of waste material in a packed bed configuration with 5% porosity, for example, can bring down the storage material costs to 2%–3% of the costs of a liquid metal‐only storage system. Furthermore, future application fields beyond concentrating solar power are proposed: supply of industrial process heat, waste heat integration and power‐to‐heat‐to‐power processes.

Poly(N‐acryloyl glycinamide) eutectogels

AbstractThe ever‐growing demand for advanced implantable and wearable electronics has stimulated the development of conductive gels with desirable functions. Hydrogels suffer from poor environmental adaptability. The ionogels prepared by dissolving polymers in ionic liquids have to face the problems of high cost of synthesis and biotoxicity concerns. Recently, eutectogels consisting of various polymer networks in eco‐friendly and cost‐effective deep eutectic solvents (DESs) have emerged as attractive alternatives to overcome the limitations associated with conventional hydrogels and ionogels. In this study, a kind of eutectogels was designed and synthesized through one‐step in situ photopolymerization of N‐acryloyl glycinamide (NAGA) without crosslinkers in low‐cost and biosafe DESs composed of choline chloride and ethylene glycol. The obtained poly(N‐acryloyl glycinamide) (PNAGA) eutectogels exhibit concentration‐dependent and adjustable mechanical properties, high electrical conductivity (about 2 mS cm−1), self‐healing ability as well as good anti‐drying and anti‐freezing properties. PNAGA eutectogels were also demonstrated to serve as conductive gels to construct pressure sensors over a relatively large temperature range. Considering the simple and easy‐to‐scale preparation process and commercially available low‐cost raw materials, favorable flexibility, high ionic conductivity, and wide‐climate tolerance, the PNAGA eutectogels as soft conductive materials have great potential for use in the fabrication of flexible electronics.

Solidification of the Ni-based superalloy CMSX-4 simulated with full complexity in 3-dimensions

In this work, we present phase-field (PF) simulations directly coupled to thermodynamic and kinetic databases in three dimensions. The direct coupling allows consideration of the full alloy complexity of the CMSX-4 superalloy over a large range of temperatures. The simulation conditions are chosen for additive manufacturing utilizing Electron Beam Melting (EBM). Transformation of interdendritic liquid into eutectic γ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma '$$\\end{document} is considered. The simulation results confirm the unique segregation behavior of all the alloying elements. It is demonstrated that the treatment of the full complexity of alloy composition is superior to all approximations with quasi-binary or -ternary approximation and justifies the significantly increased computational effort. Our results demonstrate that multi-component simulations must become a standard for phase-field applications to real material systems.

Magnetocaloric effect of Sr2FeMoO6 with an extremely broad temperature range

A phenomenological model is used to predict the magnetocaloric (MC) effect of Sr2FeMoO6. The MC characteristics of Sr2FeMoO6 are derived from simulation results for thermomagnetization in 0.05 T magnetic field. The full-width at half-maximum of 192 K is outstanding, giving a strong foundation for running the Sr2FeMoO6 in the magnetic refrigerator (MR). Because Sr2FeMoO6 could be operated as an effective MC magnet for MR over a large temperature range, it can cover a considerable and critical temperature range, including room and cryogenic temperatures. The MC parameters of Sr2FeMoO6 are greater than those of some previous reports, inferring that Sr2FeMoO6 can function as an advantageous MC magnet for the MR.

Impact of the crystallographic variants of VO2 thin films on c- and r-cut sapphire on structural phase transition and radiofrequency properties

Vanadium dioxide exhibits a metal to insulator transition close to room temperature, making it very interesting in particular for radio frequency (RF) device applications. Here, we compare the structural and RF properties of VO2 thin films grown by magnetron sputtering on c-cut and r-cut sapphire substrates. The epitaxial growth of VO2 on c-cut sapphire gives rise to several crystallographic variants for the insulating M1 phase. Moreover, during the structural transition, simultaneous presence of both metallic and insulating phases is evidenced by x-ray diffraction over a large temperature range. Films grown on r-cut sapphire exhibit only two variants and present a very narrow temperature range of their structural transition. Interestingly, such structural differences of the films grown on c- and r-cut sapphire substrates have very little influence on their dc resistivity, while the transmission of the RF signal through the metallic phase was found much lower on c-cut than on r-cut sapphire. This supports the fact that r-cut sapphire is preferable for VO2-based RF device fabrication.

New insights into refractive indices and birefringence of undoped and MgO-doped lithium niobate crystals at high temperatures

The lithium niobate single crystal is a well-known optical material that has been employed in a wide range of photonic applications. To realize further applications of the crystal, the birefringence properties need to be determined over a large range of temperatures. We report refractive indices and birefringence properties of undoped and MgO-doped lithium niobate crystals with high accuracy using spectroscopic ellipsometry in the spectral range from 450 to 1700 nm and a temperature range from ambient temperature to 1000 °C. The birefringence results indicate a transition temperature, where the crystal transforms from an anisotropic to isotropic property, and the advance of MgO doping in the crystal, which is related to the optical damage threshold of the materials. In addition, the lattice dynamics of the crystals have been analyzed by revisiting the Raman spectroscopy. The results establish the foundation of optical properties of lithium niobate crystals, providing pathways for their photonic applications.

Crystallization mechanism of B12.5 bioactive borosilicate glasses and its impact on in vitro degradation

Understanding the thermal properties and crystallization mechanisms are crucial upon sintering of bioactive glasses. In this study, crystallization mechanism and sintering ability of S53P4-based B12.5 borosilicate glass series, containing varying amounts of magnesium and/or strontium, was assessed. Additionally, the effect of crystallization onto these glasses bioactive properties was investigated.Glasses were composed of 47.12 SiO2 - 6.73 B2O3 - 21.77-x-y CaO - 22.65 Na2O - 1.72 P2O5 - x MgO - y SrO, where x,y = 0, 5 or 10 (mol%). Thermal properties were analysed with DTA, and glass transition temperatures and onset of crystallization were determined to gain an overview of temperature range suitable for heat treatments, and for calculation of activation energies related to viscous flow and crystallization. Further, sintered bodies were formed by heat-treating coarse glass particles in large temperature range; their porosity was assessed, cross section were analysed by SEM and crystallinity was studied with XRD. To evaluate the impact of crystallization on the in vitro reactivity, dissolution studies were executed in SBF-solution up to one week, with pH and ion content of solution measured at the end of immersion. Immersed particles were studied with FTIR to observe changes in the glasses structure.The main crystallization mechanism of B12.5-based glasses was determined to be surface crystallization. While the crystallization interfered with viscous flow sintering of the pure borosilicate glass, Mg and Sr addition enabled sintering of amorphous bodies more easily and with wider temperature range. Mg in the composition especially enabled densification. In vitro studies presented that surprisingly, partially crystallized specimen were initially more reactive than the amorphous specimen.

Unveiling the magnetic structure and phase transition of Cr2CoAl using neutron diffraction

We report the detailed analysis of temperature dependent neutron diffraction pattern of the Cr2CoAl inverse Heusler alloy and unveil the magnetic structure up to the phase transition as well as its fully compensated ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using the space group I4¯m2 confirms the inverse tetragonal structure over the large temperature range from 100 to 900 K. The refinement of the magnetic phase considering the wave vector k= (0, 0, 0) reveals the ferrimagnetic nature of the sample below 730±5 K. This transition temperature is obtained from empirical power law fitting of the variation in the ordered net magnetic moment variation in intensity of (110) peak as a function of temperature. The spin configuration of the microscopic magnetic structure suggests the nearly fully compensated ferrimagnetic behavior where the magnetic moments of Cr2 are antiparallel with respect to the Cr1 and Co moments. Moreover, the observed anomaly in the thermal expansion and lattice parameters at 730±5 K suggests that the distortion in the crystal structure may play an important role in the magnetic phase transition.

Modeling temperature dependence of tensile fracture strength for rocks considering phase transition and the direct effect of thermal damage

Accurately and conveniently acquiring the tensile fracture strength of rocks at different temperatures is vital no matter for the security or economical design of deep underground engineering projects. Extensive testing in the laboratory, assisted with fitting approaches, is the main method to obtain the high-temperature tensile fracture strength in the available literature. However, the high-temperature destruction test is difficult to conduct and requires numerous time and resources. In this work, considering the main physical mechanisms such as phase transition and thermal damage that affect the tensile fracture strength of rocks at high temperatures, theoretical models for predicting their temperature-dependent tensile fracture strength (TDTFS) are established based on the Force-Heat Equivalence Energy Density Principle. The presented models achieve great prediction on the different variation trends of tensile strength below and above the phase transition temperature, as well as the corresponding sudden change of strength. For rocks without phase transition, the presented model only needs some physical parameters tested at room temperature can get a good prediction capacity on the TDTFS. Moreover, a new theoretical characterization model of the equivalent thermal damage parameter was presented and take a comparison with the previous model. Finally, the potential applications and limitations of the TDTFS model are further discussed. The application threshold of the presented TDTFS models is relatively low, and they may therefore be suitable as a method for providing a rapid and preliminary evaluation of strength at a large temperature range for rock engineering.

Polymer-coated fiber-optic Fabry-Perot interferometer-based temperature sensor with high sensitivity

In this paper, a highly sensitive temperature sensor based on polymer-coated Fabry-Perot interferometer (FPI) is proposed and demonstrated. The FPI temperature sensor consists of the end face of single-mode fiber (SMF) and the Polydimethylsiloxane (PDMS) cap on the end face. By varying the number of coatings, the thickness of the PDMS cap can be flexibly controlled to obtain FPI sensors with different cavity lengths. The temperature sensitivity is studied experimentally from −30 °C to 85 °C, and it is found that the sensor shows different sensitivity in different temperature intervals, up to 0.698 nm/°C. Compared to similarly constructed sensors, the sensor in this paper has a large temperature range while maintaining a high sensitivity. In addition, the performance of the sensor is tested by experiments and the results show that the sensor possesses the advantages of good stability, fast response time and good repeatability.

High-Temperature Energy Storage Properties of Bi0.5Na0.5TiO3-0.06BaTiO3 Thin Films

Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-BT) thin films were prepared via both chemical solution (CSD) and pulsed laser deposition (PLD). The structural, dielectric, and ferroelectric properties were investigated. High stability of the dielectric permittivity or TCC (∆ε/ε (150 °C) ≤ ±15%) over a wide temperature range from room temperature to 300 °C was obtained. Distinctly, the CSD film showed high TCC stability with variation of ±5% up to 250 °C. Furthermore, the CSD film showed an unsaturated ferroelectric hysteresis loop characteristic of the ergodic relaxor phase. However, the PLD one exhibited an almost saturated loop characteristic of the coexistence of both ergodic and non-ergodic states. The energy storage properties of the prepared films were determined using P–E loops obtained at different temperatures. The results show that these films exhibited a stable and improved energy storage density comparable to ceramic capacitors. Moreover, the CSD film exhibited more rigidity and better energy storage density, which exceeded 1.3 J/cm3 under a weak applied field of 317 kV/cm, as well as interesting efficiency in a large temperature range. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Super anti-freezing, fast-responsive nanocomposite organohydrogels with excellent mechanical properties as multifunctional sensors for human motion monitoring

Conventional hydrogel sensors are always restricted in real applications due to weakness in mechanical properties, freezing and dehydration ability, as well as limited sensing functionality. Herein, a multifunctional nanocomposite organohydrogel is constructed by polyvinyl alcohol, tannic acid green reduction of graphene oxide with ethylene glycol-water (EG/H2O) binary solvent through a common freezing-thawing process to overcome the above challenges. The organohydrogel shows favorable stretchability (369%), tensile toughness (up to 1850.48 KJ/m3) and strength (tensile/compressive strength of 603 kPa/2181.63 kPa). Meanwhile, it exhibits a super anti-freezing (−133.7 °C) and moisturizing performance. As multifunctional sensors (strain/pressure/temperature sensors), it shows stable and sensitive detection in a large temperature range, and fast response (66 ms/5 ms as a strain/pressure sensor respectively). This high-performance multifunctional organohydrogel shows promising potential in flexible electronic devices, electronic skin and soft robots.

Ring Polymer Molecular Dynamics Approach to Quantum Dissociative Chemisorption Rates.

A ring polymer molecular dynamics (RPMD) method is proposed for the calculation of the dissociative chemisorption rate coefficient on surfaces. The RPMD rate theory is capable of handling quantum effects such as the zero-point energy and tunneling in dissociative chemisorption, while it relies on classical trajectories for the simulation. Applications to H2 dissociative chemisorption are demonstrated. For the highly activated process on Ag(111), strong deviations from Arrhenius behavior are found at low temperatures and attributed to tunneling. On Pt(111), where the dissociation has a barrierless pathway, the RPMD rate coefficient is found to agree with the experimentally derived thermal sticking coefficient within a factor of 2 over a large temperature range. Significant quantum effects are also found.

Investigative comparison of R134a, R290, R600a and R152a refrigerants in conventional vapor compression refrigeration system

This work represents the performance comparison of conventional vapour compression refrigeration system (VCRS) using various refrigerants such as R134a, R152a, R600a and R290. The theoretical model has been utilized for computing work input to the compressor, refrigerating effect and coefficient of performance (COP) for R134a, R290, R600a and R152a refrigerants. This investigation has been done for the evaporator temperature range of -30 °C to 10 °C and the condenser temperature range of 40 °C to 45 °C. In this performance analysis it is seen that R290 shows favourable properties and can serve as best refrigerant among all in the group. R290 shows almost equal COP to R600a in large operating temperature range and it has very high refrigerating capacity comparatively to R134a together with its low global warming potential and ozone depletion potential. R152a and R600a also show some satisfying properties.

Exploring the high-temperature deformation behavior of monocrystalline silicon – An advanced nanoindentation study

Knowing the mechanical behavior of silicon at elevated temperatures is crucial for many high-temperature applications and processes. This work aims to expand the knowledge of these properties, especially on length scales relevant to miniaturized silicon structures. Therefore, nanoindentation experiments were performed on two differently doped (1 0 0) silicon wafers with varying oxygen content, from room temperature up to 950 °C. Residual impressions were microscopically characterized via confocal laser scanning microscopy. From this dataset covering an exceptionally large temperature range the elastic modulus and hardness as well as strain rate sensitivity, activation volume, and energy were evaluated. Generally, a change in deformation behavior can be identified between 300 °C and 400 °C. Above this transition temperature, the hardness drops exponentially. Also, the material becomes strain rate sensitive. These observations support the assumption that the deformation mechanism shifts from high-pressure phase transformation to dislocation-controlled plasticity with increasing temperature. Furthermore, a change in strain rate sensitivity, activation energy, and activation volume above 800 °C implies a further shift in the rate-controlling mechanism of dislocation motion. Lastly, the more strongly doped sample with the higher oxygen content showing higher mechanical strength is discussed regarding solid-solution strengthening and dislocation locking by oxygen atoms.

Comparison of Eight Classical Lennard-Jones-Based H2 Molecular Models in the Gas Phase at Temperatures and Pressures Relevant to Hydrogen On-Board Storage Tanks.

This work compares eight classical H2 molecular models in the gas phase taken from the existing literature. All models are based on Lennard-Jones (LJ) 12-6 terms for the van der Waals interactions and hence easier to transfer to multiphase molecular simulations than more sophisticated potentials. The H2 potentials tested include one-site, two-site, three-site, and five-site models, with the sites being either the H atoms, the center-of-mass of the H2 molecule, or massless sites. For the multisite models, high-frequency H-H stretching modes can lead to poor equipartition of the kinetic energy, and the timestep for molecular dynamics (MD) simulations should be reduced to maintain a stable numerical integration of the equations of motion. As such, only those models with rigid bonds are considered. In the present case, 600 MD simulations of H2 gas were carried out over a large range of temperatures (-50 to +90 °C) and at densities corresponding to a pressure range of 50 to 2000 bar, which include the operating conditions of on-board storage tanks in hydrogen-fueled vehicles. Most of the models under study were found to reproduce reasonably well the experimental pVT phase diagram as well as the solubility. Discrepancies only became significant at the highest densities tested, and these could be used to rank the different models. All model diffusion coefficients were essentially indistinguishable from experimental results, and as such, kinetically dominated dynamic properties could not be used as a criterion for the choice of model. Among the eight models tested, two of them, i.e., the two-site model of Yang and Zhong and the one-site model derived from Buch performed very well over the range of conditions tested. They represent a good compromise between realism, simplicity, and computational efficiency.

Alterable interferential fineness for high temperature sensing calibration based on Bragg hollow core fiber.

We propose, what we believe to be, a novel method for high temperature sensing calibration based on the mechanism of alterable interferential fineness in Bragg hollow core fiber (BHCF). To verify the proof-of-concept, the fabricated sensing structure is sandwiched by two sections with different length of BHCF. Two interferential fineness fringes dominate the transmission spectrum, where the high-fineness fringes formed by anti-resonant reflecting optical waveguide (ARROW) plays the role for high temperature measurement. Meanwhile, the low-fineness fringes induced by short Fabry-Perot (F-P) cavity are exploited as temperature calibration. The experimental results show that the ARROW mechanism-based temperature sensitivity can reach 26.03 pm/°C, and the intrinsic temperature sensitivity of BHCF is 1.02 pm/°C. Here, the relatively lower magnitude of the temperature sensitivity is considered as the standard value since it merely relies on the material properties of silicon. Additionally, a large dynamic temperature range from 100 °C to 800 °C presents linear response of the proposed sensing structure, which may shine the light on the sensing applications in the harsh environment.