Showing papers on "Atmospheric temperature range published in 2016"

A Novel Optical Thermometry Strategy Based on Diverse Thermal Response from Two Intervalence Charge Transfer States

Abstract: In this work, a novel thermometry strategy based on the diversity in thermal quenching behavior of two intervalence charge transfer (IVCT) states in oxide crystals is proposed, which provides a promising route to design self-referencing optical temperature sensing material with superior temperature sensitivity and signal discriminability. Following this strategy, uniform Tb3+/Pr3+:NaGd(MoO4)2 micro-octahedrons are directionally synthesized. Originated from the diverse thermal responses between Tb3+-Mo6+ and Pr3+-Mo6+ IVCT states, fluorescence intensity ratio of Pr3+ to Tb3+ in this material displays excellent temperature sensing property in a temperature range from 303 to 483 K. The maximum absolute and relative sensitivity reaches as high as 0.097 K−1 and 2.05% K−1, respectively, being much higher than those of the previously reported optical thermometric materials. Excellent temperature sensing features are also demonstrated in the other Tb3+/Pr3+ codoped oxide crystals having d0 electron configured transition metal ions (Ti4+, V5+, Mo6+, or W6+), such as scheelite NaLu(MoO4)2 and NaLu(WO4)2, and monazite LaVO4 and perovskite La2Ti3O9, evidencing the universal validity of the proposed strategy. This work exploits an effective pathway for developing new optical temperature sensing materials with high performance.

Structural and optical properties of methylammonium lead iodide across the tetragonal to cubic phase transition: implications for perovskite solar cells

Abstract: We report temperature resolved UV-vis absorption and spectral photocurrent response measurements of MAPbI3 thin films and solar cells, together with ab initio simulations, to investigate the changes in material properties occurring across the tetragonal to cubic phase transition. We find that the MAPbI3 band-gap does not abruptly change when exceeding the tetragonal to cubic transition temperature, but it rather monotonically blue-shifts following the same temperature evolution observed within the tetragonal phase. Car–Parrinello molecular dynamics simulations demonstrate that the high temperature phase corresponds on average to the expected symmetric cubic structure assigned from XRD measurements, but that the system strongly deviates from such a structure in the sub-picosecond time scale. Thus, on the time scale of electronic transitions, the material seldom experiences a cubic environment, rather an increasingly distorted tetragonal one. This result explains the absence of dramatic changes in the optical of MAPbI3 across the explored temperature range of 270–420 K, which could have important consequences for the practical uptake of perovskite solar cells.

Broad temperature plateau for high ZTs in heavily doped p-type SnSe single crystals

Abstract: Excellent thermoelectric performance is obtained over a broad temperature range from 300 K to 800 K by doping single crystals of SnSe. The average value of the figure of merit ZT, of more than 1.17, is measured from 300 K to 800 K along the crystallographic b-axis of 3 at% Na-doped SnSe, with the maximum ZT reaching a value of 2 at 800 K. The room temperature value of the power factor for the same sample and in the same direction is 2.8 mW mK−2, which is an order of magnitude higher than that of the undoped crystal. Calculations show that Na doping lowers the Fermi level and increases the number of carrier pockets in SnSe, leading to a collaborative optimization of the Seebeck coefficient and the electrical conductivity. The resultant optimized carrier concentration and the increased number of carrier pockets near the Fermi level in Na-doped samples are believed to be the key factors behind the spectacular enhancement of the average ZT.

Electromagnetic Property and Tunable Microwave Absorption of 3D Nets from Nickel Chains at Elevated Temperature

Abstract: We fabricated the nickel chains by a facile wet chemical method. The morphology of nickel chains were tailored by adjusting the amount of PVP during the synthesis process. Both the complex permittivity and permeability of the three-dimensional (3D) nets constructed by nickel chains present strong dependences on temperature in the frequency range of 8.2–12.4 GHz and temperature range of 323–573 K. The peaks in imaginary component of permittivity and permeability mainly derive from interfacial polarizations and resonances, devoting to dielectric and magnetic loss, respectively. The effect from both dielectric and magnetism contribute to enhancing the microwave absorption. The maximum absorption value of the 3D nickel chain nets is approximately −50 dB at 8.8 GHz and 373 K with a thickness of 1.8 mm, and the bandwidth less than −10 dB almost covers the whole investigated frequency band. These are encouraging findings, which provide the potential advantages of magnetic transition metal-based materials for mic...

Large electrocaloric response and high energy-storage properties over a broad temperature range in lead-free NBT-ST ceramics

Abstract: The improvement of the electrocaloric effect (ECE) in (1−x)(Na0.5Bi0.5)TiO3−xSrTiO3 (NBT-ST) lead-free relaxor ferroelectric ceramics was determined by indirect measurements method and is reported here. The phase transition temperature can be reduced to room temperature by tuning the compositions of the (1−x)NBT-xST material. A large ECE (ΔTmax = 1.64 K, ΔSmax = 2.52 K and ΔT/ΔE = 0.33 K mm kV−1 at 50 kV cm−1) was obtained at 60 °C when x = 0.25. A suitable response over a broad temperature range from 30 °C to 70 °C can be obtained with x = 0.26 with very high cooling values (ΔT > 1 K). In addition, the 0.7NBT-0.3ST AFE-like bulk ceramic exhibited excellent temperature stability in its energy-storage properties from room temperature to 120 °C. The maximum value of the recoverable energy density was 0.65 J/cm3 obtained at 65 kV/cm. Taken together, these properties signified that (1−x)NBT-xST is a promising material for applications in cooling systems and energy-storage in the room temperature range.

Temperature-dependent capacitance–voltage and current–voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n––Ga2O3 drift layers grown by halide vapor phase epitaxy

Abstract: We investigated the temperature-dependent electrical properties of Pt/Ga2O3 Schottky barrier diodes (SBDs) fabricated on n–-Ga2O3 drift layers grown on single-crystal n+-Ga2O3 (001) substrates by halide vapor phase epitaxy. In an operating temperature range from 21 °C to 200 °C, the Pt/Ga2O3 (001) Schottky contact exhibited a zero-bias barrier height of 1.09–1.15 eV with a constant near-unity ideality factor. The current–voltage characteristics of the SBDs were well-modeled by thermionic emission in the forward regime and thermionic field emission in the reverse regime over the entire temperature range.

Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr 3 quantum dots.

Abstract: Recently, lead halide perovskite quantum dots have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) has been studied at a broad temperature range, from 80 to 380 K. Two-photon absorption has been investigated and the absorption coefficient is up to 0.085 cm/GW at room temperature. Moreover, the PL spectrum excited by two-photon absorption shows a linear blue-shift (0.32 meV/K) below the temperature of 220 K. However, for higher temperatures, the PL peak approaches a roughly constant value and shows temperature-independent chromaticity up to 380 K. This behavior is distinct from the general red-shift for semiconductors and can be attributed to the result of thermal expansion, electron–phonon interaction and structural phase transition around 360 K. The strong nonlinear absorption and temperature-independent chromaticity of CsPbBr3 QDs observed in temperature range from 220 to 380 K will offer new opportunities in nonlinear photonics, light-harvesting, and light-emitting devices.

A Centrosymmetric Hexagonal Magnet with Superstable Biskyrmion Magnetic Nanodomains in a Wide Temperature Range of 100–340 K

Abstract: Superstable biskyrmion magnetic nanodomains are experimentally observed for the first time in a hexagonal MnNiGa, a common and easily produced centrosymmetric material. The biskyrmion states in MnNiGa thin plates, as determined by the combination of in situ Lorentz transmission electron microscopy images, magnetoresistivity, and topological Hall effect measurements, are surprisingly stable over a broad temperature range of 100-340 K.

High performance thermoelectric materials and devices based on GeTe

Abstract: Thermoelectric materials have received recent attention due to their ability to convert waste heat to electrical energy directly and reversibly. Inorganic materials, especially Bi2Te3, PbTe and Si–Ge based alloys, have been investigated in the temperature range of 300–1000 K, among which PbTe based materials have been extensively studied, and reported to be the leading thermoelectric materials for mid-temperature power generation. However, environmental concern limits their large scale production due to the toxic nature of Pb. As an alternative, GeTe-rich alloys such as TAGS (GeTe–AgSbTe2) have been largely investigated since the 1960s. Most recently, some of the new materials in the GeTe family have been introduced such as Ge0.87Pb0.13Te, the homologous series of Sb2Te3(GeTe)n and Ge0.9Sb0.1Te, and are reported to exhibit high thermoelectric performance, inherently formed nano and microstructure modulations, and high thermal and mechanical stability. These collective enhanced properties of GeTe-rich alloys have generated great interest in investigating further new GeTe based alloys for intermediate temperature thermoelectric applications. In order to provide the fundamental understanding, technological insights, and to further promote the GeTe based alloys, we hereby present a review on (i) the crystal structure, nano/microstructure, phase transition, electronic structure, and thermoelectric properties of GeTe, (ii) correlation of compositional and microstructure modulations and thermoelectric properties of doped GeTe, TAGS based alloys, Ge–Pb–Te materials, and Ge–Sb–Te materials, (iii) mechanical properties, (iv) past and present devices based on GeTe materials and (v) future directions.

Temperature-dependent photoluminescence of inorganic perovskite nanocrystal films

Abstract: Temperature-dependent photoluminescence (PL) properties of inorganic perovskite CsPbBr3 nanocrystal (NC) films were studied by using steady-state and time-resolved PL spectroscopy. The closely packed solid films were obtained by dropping NC solution on silicon substrates. It was found that the PL intensities of the NC films, which are dependent on the size of NCs, slightly decreased with increasing temperature to 300 K, while the PL intensities dropped rapidly with increasing temperature above 300 K and were nearly quenched at 360 K. Further the corresponding average PL lifetimes increased significantly with increasing temperature below about 320 K and then significantly became shorter. The PL quenching mechanisms were demonstrated through heating and cooling experiments. The experimental results indicated inorganic perovskite NCs exhibited a thermal PL quenching in the temperature range of 80–300 K and a thermal degradation at temperatures above 300 K. The linewidths, peak energies, and lifetimes of PL emissions for the NC films as a function of temperature were discussed in detail.

Tellurium-Assisted Epitaxial Growth of Large-Area, Highly Crystalline ReS2 Atomic Layers on Mica Substrate.

Abstract: Anisotropic 2D layered material rhenium disulfide (ReS2 ) with high crystal quality and uniform monolayer thickness is synthesized by using tellurium-assisted epitaxial growth on mica substrate. Benefit from the lower eutectic temperature of rhenium-tellurium binary eutectic, ReS2 can grow from rhenium (melting point at 3180 °C) and sulfur precursors in the temperature range of 460-900 °C with high efficiency.

Temperature sensor realized by inkjet printing process on flexible substrate

Abstract: The objective of this study is to realize a printed and flexible temperature sensor to achieve surface temperature measurement of the human body. The sensor is a thermistor composed silver (Ag) deposited on a Polyimide substrate (Kapton HN). The meander was patterned by inkjet printing with a drop-on-demand Jetlab4 (Microfab Technologies Inc.). The resistance temperature coefficients have been studied in the temperature range of 20–60 °C with a range of voltage between 0 and 1 V. The stability versus time has also been measured without a sensor layer protection. The sensitive area of the sensor, silver lines width and the gap between the electrical conductors were, respectively 6.2 cm 2 , 300 μm, 60 μm. The mean temperature sensor sensitivity found was 2.23 × 10 −3 °C −1 . The results show a good linearity and less than 5% hysteresis in the extended measurement.

Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB.

Abstract: The ‘MAlB’ phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36–0.49 μΩm) and – like a metal – drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm−1K−1 at 26 °C). In the 25–1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10−6K−1. Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.

Temperature-dependent excitonic photoluminescence Excited by Two-Photon Absorption in Perovskite CsPbBr3 Quantum Dots

Abstract: Recently lead halide nanocrystals (quantum dots) have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) have been studied across a broad temperature range from 80K to 380K. Two-photon absorption has been investigated with absorption coefficient up to 0.085 cm/GW at room temperature. Moreover, the photoluminescence excited by two-photon absorption shows a linear blue-shift (0.25meV/K) below temperature of ~220K and turned steady with fluctuation below 1nm (4.4meV) for higher temperature up to 380K. These phenomena are distinctly different from general red-shift of semiconductor and can be explained by the competition between lattice expansion and electron-phonon couplling.Our results reveal the strong nonlinear absorption and temperature-independent chromaticity in a large temperature range from 220K to 380K in the CsPbX3 QDs, which will offer new opportunities in nonlinear photonics, light-harvesting and light-emitting devices.

Promotional effects of zirconium doped CeVO4 for the low-temperature selective catalytic reduction of NOx with NH3

Abstract: In this work, we developed a novel zirconium doped CeVO 4 to form Ce 1− x Zr x VO 4 ( x = 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 0.70, 0.80) solid solution as a low-temperature catalyst for the selective catalytic reduction (SCR) of NO x with NH 3 . The optimized catalysts showed excellent performance at low temperature. The light-off temperature (the temperature at which the conversion of NO reaches 50%) was down to about 125 °C, while the temperature window (the NO conversion is above 80%) ranged from 150 to 375 °C. The selectivity was kept close to 100% during the whole temperature range. Furthermore, the catalysts also exhibited good H 2 O/SO 2 durability and fascinating performance at high gas hourly space velocity of 400,000 h −1 . Hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, ammonia and nitrogen oxides temperature-programmed desorption and in-situ diffuse reflectance infrared Fourier transform experiments were performed to study the influence of Zr doping on the SCR performance. It was found that the introduction of Zr in CeVO 4 with a proper amount could significantly increase the surface area, oxidative ability, active oxygen species and especially surface acid sites of the catalysts, which were beneficial to the promotion of SCR performance.

Impedance and Modulus Spectroscopy Characterization of Tb modified Bi0.8A0.1Pb0.1Fe0.9Ti0.1O3 Ceramics

Abstract: In this paper we present the impedance spectroscopy of ternary solid solutions of BiFeO3, TbFeO3 and PbTiO3, prepared by solid-state reaction method. The preliminary structural studies were carried out by x-ray diffraction technique, showing the formation of polycrystalline sample with ABO3 type of perovskite structure with hexagonal symmetry for Bi0.8Tb0.1Pb0.1Fe0.9Ti0.1O3system at room temperature. Dielectric and impedance study of this ceramic has been characterized in the temperature range 175 - 325 0C and frequency range 100 Hz - 1 MHz. The maximum ferroelectric transition temperature (Tc) of this system was in the range 210 - 225 0C with the dielectric constant having maximum value ~2480 at 1 kHz. The complex impedance graph exhibited one impedance semicircle arc at all reported temperatures, which indicates that the impedance response is a Cole-Cole type relaxation. Single semicircle indicate that the grain effect of the bulk in ceramic. The bulk resistance of the material decreases with increasing temperature showing negative temperature showing a typical semiconducting property, i.e. negative temperature coefficient of resistance (NTCR) behavior.

Improvement of dielectric and energy storage properties in Bi(Mg1/2Ti1/2)O3-modified (Na1/2Bi1/2)0.92Ba0.08TiO3 ceramics

Abstract: Dielectric materials with stable dielectric and energy storage properties at a high operating temperature are needed in many important applications, such as the capacitors used in the automotive and aerospace industries. Between Td, the phase transition temperature from a ferroelectric phase to a high-temperature non-polar or weakly polar phase, and Tm, the maximum temperature of the dielectric constant, Na1/2Bi1/2TiO3-based ferroelectric materials exhibit a relatively small variation in their dielectric properties, a feature of this type of material. Here we will demonstrate that by incorporating Bi(Mg1/2Ti1/2)O3 into Na1/2Bi1/2TiO3-based ceramics, the temperature range between Td and Tm can be expanded, leading to a smaller variation of the dielectric and energy storage properties over a wider temperature range compared with the materials without modification. Bi(Mg1/2Ti1/2)O3 modification can also greatly increase the discharge energy density and charge-discharge efficiency of the materials. The 10 mol% Bi(Mg1/2Ti1/2)O3 modified (Na1/2Bi1/2)0.92Ba0.08TiO3 ceramics exhibit a small variation of dielectric constant and low loss from 100 °C to 400 °C. The materials also exhibit a high energy density (>2 J/cm3) and a high charge-discharge efficiency (>88%) at 120 °C. The energy density of the materials is almost independent of temperature from room temperature to 180 °C, which is attractive for high-temperature dielectric and energy storage applications.

Carbon nanotube-CdS core-shell nanowires with tunable and high-efficiency microwave absorption at elevated temperature.

Abstract: Tuning microwave absorption to meet the harsh requirement of thermal environments is a great challenge. Three kinds of nanowires, including multi-walled carbon nanotubes (MWCNTs) coated with CdS nanocrystals (CdS-MWCNTs), and MWCNTs coated with different-thickness CdS sheaths, have been synthesized through mild solution-process synthesis. The influence of CdS amount, external temperature, loading concentration and sample thickness on the absorption performance were studied. The composite loading with 6 vol.% CdS-MWCNTs shows the best absorption of −47 dB at 473 K with a thickness of 2.6 mm in the temperature range of 323–573 K and X band. The effective bandwidth covers the full X band in 323–473 K for RL ≤ −20 dB and reaches 2.0 GHz at 473 K for RL ≤ −20 dB. The enhanced absorption ability of CdS-MWCNTs arises from the effective impedance matching, benefiting from abundant interfacial polarization from the added CdS nanocrystals and the changeable dielectric property at elevated temperature. The results indicate that the CdS-MWCNT is a promising functional material for high temperature microwave absorption.

Enhanced mid-temperature thermoelectric performance of textured SnSe polycrystals made of solvothermally synthesized powders

Abstract: This work revealed that the thermoelectric properties of textured SnSe polycrystals, which are made of solvothermally synthesized powders with a preferred orientation grown along the (400) plane, can be enhanced, especially in the range of mid-temperatures. The electrical conductivity for the sintered sample is greatly improved in the whole measured temperature range, attributed to the high carrier concentration and unique mobility change. This results in a large power factor combined with the moderate Seebeck coefficient, especially in the range of 300–650 K, which exceeds 5 μW cm−1 K−2 at 423 K and even larger than 6 μW cm−1 K−2 at 521 K. Benefiting from the enhanced electrical conductivity and the low total thermal conductivity (<1 W m−1 K−1 in the range of 300 to 773 K), a higher ZT value than that reported for undoped single crystals was achieved in a relatively wide mid-temperature range, which reached 0.44 at 522 K and 0.5 at 573 K, and then showed weak temperature dependence in the range from 573 to 700 K. Above 700 K, the ZT value increased with temperature and a maximum value of nearly 0.6 was obtained at the maximum measured temperature of 773 K for the SnSe sample without any deliberate doping.

Attaining high mid-temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization

Abstract: For decades, zone-melted Bi2Te3-based alloys have been the most widely used thermoelectric materials with an optimal operation regime near room temperature. However, the abundant waste heat in the mid-temperature range poses a challenge; namely, how and to what extent the service temperature of Bi2Te3-based alloys can be upshifted to the mid-temperature regime. We report herein a synergistic optimization procedure for Indium doping and hot deformation that combines intrinsic point defect engineering, band structure engineering and multiscale microstructuring. Indium doping modulated the intrinsic point defects, broadened the band gap and thus suppressed the detrimental bipolar effect in the mid-temperature regime; in addition, hot deformation treatment rendered a multiscale microstructure favorable for phonon scattering and the donor-like effect helped optimize the carrier concentration. As a result, a peak value of zT of ~1.4 was attained at 500 K, with a state-of-the-art average zTav of ~1.3 between 400 and 600 K in Bi0.3Sb1.625In0.075Te3. These results demonstrate the efficacy of the multiple synergies that can also be applied to optimize other thermoelectric materials. A popular material for converting heat into electricity can now operate at elevated temperatures associated with industrial machinery. Bismuth tellurium is a thermoelectric alloy that works at room temperature and finds use in refrigeration and powergeneration, but much waste heat is created in the so-called middle temperature range of 100–300 degrees Celsius. Tiejun Zhu from Zhejiang University and colleagues doped indium atoms into bismuth tellurium to provide a balance to the excess, thermally activated charge carriers that normally materialize when this alloy is heated to middle temperatures. Hot deformations of the alloy during fabrication introduced missing-atom defects and micrograins that worked together with dopants to scatter heat-transporting phonon waves and optimize carrier concentrations. Thermoelectric and X-ray testing revealed that the doped alloyhad a higher working temperature and better mechanical properties. We herein report a synergistic optimization procedure that combines point defect engineering, band structure engineering and multiscale microstructuring in p-type (Bi,Sb)2Te3 thermoelectric materials by Indium doping and hot deformation. As a result, a peak value of zT ~1.4 was attained in Bi0.3Sb1.625In0.075Te3 at 500 K, along with a state-of-the-art average zTav of ~1.3 between 400 and 600 K. These results demonstrate the efficacy of the multi-synergies that can also be applied to optimize other thermoelectric materials.

Temperature dependent behaviour of lead sulfide quantum dot solar cells and films

Abstract: Despite increasing greatly in power conversion efficiency in recent times, lead sulfide quantum dot (PbS QD) solar cells still suffer from a low open circuit voltage (VOC) and fill factor (FF). In this work, we explore the temperature dependent behavior of ∼9% efficient solar cells. In the temperature range of 290 to 230 K, we find increased VOC and FF values without significant degradation of the short circuit current, leading to up to 10.3% efficiency at 230 K. The change in VOC is driven by the decrease of the reverse saturation current which fits the PN-junction model. Using Schottky and single carrier devices, we measure the carrier mobility, diffusion lengths, and doping concentrations of PbS QD films with tetrabutylammonium iodide and ethane dithiol ligands as a function of temperature. Both mobility and diffusion length are found to decrease with decreasing temperature while device performance increases, indicating that the 260 nm thick active layer is fully depleted. Finally, we propose that further optimization of the doping concentrations could help achieve increased device performance at room temperature.

Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts.

Abstract: The replacement of precious metals in catalysis by earth-abundant metals is currently one of the urgent challenges for chemists. Whereas palladium-catalyzed copolymerization of ethylene and polar monomers is a valuable method for the straightforward synthesis of functionalized polyolefins, the corresponding nickel-based catalysts have suffered from poor thermal tolerance and low molecular weight of the polymers formed. Herein, we report a series of neutral nickel complexes bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands. The Ni/IzQO system can catalyze ethylene polymerization at 50-100 °C with reasonable activity in the absence of any cocatalyst, whereas most known nickel-based catalysts are deactivated at this temperature range. The Ni/IzQO catalyst was successfully applied to the copolymerization of ethylene with allyl monomers to obtain the corresponding copolymers with the highest molecular weight reported for a Ni-catalyzed system.

Polycrystal anelasticity at near-solidus temperatures

Abstract: Elasticity, anelasticity, and viscosity of polycrystalline aggregates were measured at the near-solidus temperatures ranging from below to above the solidus temperature (Tm). The result shows that the mechanical effects of the partial melting are twofold; changes just below the solidus temperature in the absence of melt and changes at the solidus temperature due to the onset of partial melting. As homologous temperature (T/Tm) increases from about 0.92 to 1, high-frequency part of the attenuation spectrum significantly grows. Viscosity of the grain boundary diffusion creep is also reduced in this temperature range. These changes are caused by a solid-state mechanism and have a large amplitude even for the samples which can generate very small amounts of melt at the solidus temperature. At the onset of melting, further increases in the elastic, anelastic, and viscous compliances occur. These changes are caused by the direct effects of the melt phase and are very small for the samples with very small melt fractions. Mechanical properties of a partially molten aggregate are determined by these twofold changes, and when melt fraction is small, the former changes are dominant. We performed a parameterization of the present experimental results and applied the obtained empirical formula to the seismic tomographic data in the upper mantle. The present model explains well the steep reduction of the seismic shear wave velocity in the oceanic lithosphere just below the solidus temperature.

Temperature-dependent optical properties of gold thin films

Abstract: Understanding the temperature dependence of the optical properties of thin metal films is critical for designing practical devices for high temperature applications in a variety of research areas, including plasmonics and near-field radiative heat transfer. Even though the optical properties of bulk metals at elevated temperatures have been studied, the temperature-dependent data for thin metal films, with thicknesses ranging from few tens to few hundreds of nanometers, is largely missing. In this work we report on the optical constants of single- and polycrystalline gold thin films at elevated temperatures in the wavelength range from 370 to 2000 nm. Our results show that while the real part of the dielectric function changes marginally with increasing temperature, the imaginary part changes drastically. For 200-nm-thick single- and polycrystalline gold films the imaginary part of the dielectric function at 500 °C becomes nearly twice larger than that at room temperature. In contrast, in thinner films (50-nm and 30-nm) the imaginary part can show either increasing or decreasing behavior within the same temperature range and eventually at 500 °C it becomes nearly 3-4 times larger than that at room temperature. The increase in the imaginary part at elevated temperatures significantly reduces the surface plasmon polariton propagation length and the quality factor of the localized surface plasmon resonance for a spherical particle. We provide experiment-fitted models to describe the temperature-dependent gold dielectric function as a sum of one Drude and two critical point oscillators. These causal analytical models could enable accurate multiphysics modelling of gold-based nanophotonic and plasmonic elements in both frequency and time domains.

Metal–organic frameworks with a large breathing effect to host hydroxyl compounds for high anhydrous proton conductivity over a wide temperature range from subzero to 125 °C

Abstract: It is important but still challenging to develop high-performance proton conducting materials for proton exchange membrane fuel cells (PEMFCs), as such materials should meet the following requirements: stable proton-transport pathway over a wide temperature range, high conductivity at work temperature, and small activation energy Ea to maintain high conductivity at start temperature. Here, we firstly demonstrated that flexible metal–organic frameworks (FMOFs) are good hosts to seek out better proton carriers for such high-performance proton conducting materials. A FMOF [Zn3(tz)2(bdc)2]n (FJU-31, Htz = 1H-1,2,3-triazole, H2bdc = terephthalic acid) with high thermal stability up to 400 °C, which can be readily synthesized from the Zn5(tz)6(NO3)4 precursor and H2bdc, has been employed to host various organic hydroxyls as new proton carriers. Three resulting FMOFs Zn3(tz)2(bdc)2@G (FJU-31@G, G = hydroquinone (Hq), cyclohexanol (Ch) or butanol (Bu)) show large breathing effect amplitudes up to 65% and guest-related single-crystal to single-crystal structural transformations by temperature stimulus. Most importantly, FJU-31@Hq hosting hydroquinone with a high melting point and small pKa exhibits a high anhydrous proton conductivity of 2.65 × 10−4 S cm−1, low activation energy Ea of 0.18 eV, and the widest temperature range from −40 to 125 °C for stable proton conduction among the crystalline porous materials.