Remarkable Temperature Dependence Research Articles

Insights into the Thermal Expansion of Amorphous Polymers.

We investigated the thermal expansion of amorphous polystyrene (PS) and poly(methyl methacrylate) (PMMA) homopolymers using the temperature dependence of spatial electron-density correlations. The strong and broad X-ray interference maxima arising from inter- and intramolecular correlation distances were distinct, maintaining their shape during the heating of the samples to 250 °C. Three maxima characteristic of electron density correlations between the backbones, substituents along the chain, and repeat-units were observed. A remarkable temperature dependence was identified in the largest correlation distances arising from the intermolecular interactions. Based on the temperature dependence of the correlation distances, the coefficients of molecular expansion were very close to the coefficients of thermal expansion. This study provides a simple yet accurate way to correlate macroscopic volume expansions with the molecular expansion obtained from wide-angle X-ray scattering (WAXS) data.

Poisson's Ratio of Glasses, Ceramics, and Crystals.

Poisson's ratio is the fundamental metric used to discuss the performance of any material when strained elastically. However, the methods of the determination of Poisson's ratio are not yet discussed well. The first purpose of this paper is to introduce the five kinds of typical experimental methods to measure Poisson's ratio of glasses, ceramics, and crystals. The second purpose is to discuss the experimental results on the variation of Poisson's ratio by composition, temperature, and pressure reviewed for various glasses, ceramics, and crystals, which are not yet reviewed. For example, in oxide glasses, the number of bridging oxygen atoms per glass-forming cation provides a straightforward estimation of network crosslinking using Poisson's ratio. In the structural-phase transition of crystals, Poisson's ratio shows remarkable temperature-dependence in the vicinity of a phase-transition temperature. The mechanism of these variations is discussed from physical and chemical points of view. The first-principles calculation of Poisson's ratio in the newly hypothesized compounds is also described, and its pressure-induced ductile-brittle transition is discussed.

Thermally activated plastic deformation of Si single crystals at temperatures above 1173 K

The effect of high-temperature heat treatment during production on the mechanical property of Si wafer, namely yield stress, was studied through tensile tests of Si single crystals at 1123–1373 K, where stress–strain curves were obtained along the and directions. The critical resolved shear stress showed a remarkable temperature dependence, and it decreased with increasing test temperature. Below 1348 K, the activation enthalpy determined through strain rate jump tests showed no significant difference between crystals made by the Chokralski and the floating zone methods. This indicated that the solute oxygen does not influence the thermally activated dislocation glides. The activation enthalpy of 4.9 eV for a dislocation glide was much higher than that reported by previous studies (2.2 eV at temperatures below 1100 K), indicating that the thermal activation of dislocation glide is different from kink-pair nucleation. It was found that self-diffusion can assist the dislocation glide at temperatures above 1130 K.

Investigation of the phonon dispersion associated with superlattice reflections in the BiS2 -based superconductor LaBiS2O0.5F0.5

The phonon dispersion of a $\mathrm{Bi}{\mathrm{S}}_{2}$-based superconductor $\mathrm{La}\mathrm{Bi}{\mathrm{S}}_{2}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}$ is investigated by first-principles calculations and inelastic x-ray scattering experiments. The origin of superlattice (SL) reflections arising from transverse-type lattice modulation, which were recently reported in [J. Kajitani et al., J. Phys. Soc. Jpn. 90, 103601 (2021)], is discussed in terms of lattice dynamics. Our first-principles calculations of phonon dispersion and the Fermi surfaces (FSs) demonstrate that the phonon mode corresponding to the transverse-type lattice modulation is unstable, and the propagation vector corresponding to the SL reflections is close to the FS nesting vector, which suggests that the phonon softening originates from the FS nesting. Against these calculated expectations, measured phonon dispersion in $\mathrm{La}\mathrm{Bi}{\mathrm{S}}_{2}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}$ along the Z-A direction, where the SL point is located, shows no remarkable temperature dependence, and there are no steeply declining branches accompanied with a softening around the SL point. Based on these results, we discuss the two possibilities for the transverse lattice modulation in $\mathrm{La}\mathrm{Bi}{\mathrm{S}}_{2}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}$: the order-disorder-type structural transition and the displacive structural transition with an overdamped mode, for both of which the local structure distortion or the short-range correlation within the $\mathrm{Bi}{\mathrm{S}}_{2}$ plane would be essential.

Temperature-sensitive lanthanide-doped core-multishell nanocrystals with excitation-wavelength-dependent bimodal luminescence thermo-behaviors and their application in dynamic anticounterfeiting

Herein, we constructed a sort of particular lanthanide-doped core-multishell nanocrystals, NaErF4:0.5%Tm@NaYF4 @NaYF4:50%Yb,2%Ho@NaYF4:50%Yb (CSSS-UCNPs), which first integrated bimodal temperature-dependent UC emissions and orthogonal luminescence triggered by dual NIR lasers. Specifically, CSSS-UCNPs respectively presented strong yellowish green (Ho3++Er3+) and red luminescence (Er3+) under 980 nm and 1550 nm excitations via regulating constructional parameters. Moreover, the photoluminescence of CSSS-UCNPs showed remarkable temperature dependence, and luminescence thermo-behaviors changed with excitation wavelengths: thermo-enhanced Ho3+ green luminescence under 980 nm irradiation, and thermo-quenched Er3+ red luminescence under 1550 nm excitation. The unexpected thermal intensification of Ho3+ luminescence in CSSS-UCNPs of such large dimension (>>50 nm) violated the available literature involving size-dependent thermal enhancement. It’s discovered that the heat-induced vibration attenuation of oleate ligands mainly contributed to 980 nm-excited thermal intensification, which had never been reported before. Thanks to their unique excitation/temperature-responsive luminescence, the printed patterns by CSSS-UCNPs displayed noticeable changes in brightness and chromaticity under NIR excitations when raising the temperature. Briefly, this work affords a promising candidate for high-security-level anticounterfeiting, and, more importantly, supplies new perspectives on anomalous thermal enhancement in large-sized Yb3+-sensitized UCNPs.

The hydrogen bond continuum in solid isonicotinic acid

The understanding and correct description of intermolecular hydrogen bonds are crucial in the field of multicomponent pharmaceutical solids, such as salts and cocrystals. Solid isonicotinic acid can serve as a suitable model for the development of methods that can accurately characterize these hydrogen bonds. Experimental solid-state NMR has revealed a remarkable temperature dependence and deuterium-isotope-induced changes of the chemical shifts of the atoms involved in the intermolecular hydrogen bond; these NMR data are related to changes of the average position of the hydrogen atom. These changes of NMR parameters were interpreted using periodic DFT path-integral molecular dynamics (PIMD) simulations. The small size of the unit cell of isonicotinic acid allowed for PIMD simulations with the computationally demanding hybrid DFT functional. Calculations of NMR parameters based on the hybrid-functional PIMD simulations are in excellent agreement with experiment. It is thus demonstrated that an accurate characterization of intermolecular hydrogen bonds can be achieved by a combination of NMR experiments and advanced computations.

Tuning of circular photogalvanic effect of surface states in the topological insulator Sb2Te3 via structural deformation

Strain is a useful method to manipulate properties of three-dimensional (3D) topological insulators (TIs). In this study, we demonstrate the possibility to tune the circular photogalvanic effect (CPGE) of surface states of 3D TI Sb2Te3 films by applying external strain. The CPGE of 3D TI Sb2Te3 grown on SrTiO3 (STO) with different thicknesses has been systematically investigated. It is found that as the thickness of Sb2Te3 films increases from 7-quintuple layer (QL) to 27-QL, the CPGE current first increases and then decreases. Additionally, the CPGE currents demonstrate remarkable temperature dependence, which even reverse sign when the temperature is increased from 77 to 300 K. This phenomenon is due to the vertical thermoelectric effect and inverse spin Hall effect. Finally, the CPGE measurements of Sb2Te3 films under different mechanical strains are performed, and it is found that the CPGE current linearly decreases with the increase in the external strain. The variation in the CPGE current can be tuned up to 11% and 44% in the 18- and 12-QL Sb2Te3 grown on STO substrates under a tensile strain of 0.0225 and 0.0066, respectively. In particular, it can even reach 100% in the 30-QL Sb2Te3 film grown on an InP substrate under a tensile strain of 0.0033, which is due to the combined effect of mechanical deformation and spin injection from substrates. Our work provides a method to effectively manipulate the CPGE in 3D TIs by the combined effect of mechanical strain and spin injection from substrates, which paves the way for novel opto-spintronic devices.

Mode-specific quantum dynamics study of OH + H2S → H2O + SH reaction

The hydrogen abstraction reaction from H2S by OH is of key importance in understanding of the causes of acid rain, air pollution, and climate change. In this work, the reaction OH+H2S → H2O+SH is investigated on a recently developed ab initio-based globally accurate potential energy surface by the time-dependent wave packet approach under a reduced-dimensional model. This reaction behaves like a barrier-less reaction at low collision energies and like an activated reaction with a well-defined barrier at high collision energies. Exciting either the symmetric or antisymmetric stretching mode of the molecule H2S enhances the reactivity more than exciting the bending mode, which is rationalized by the coupling strength of each normal mode with the reaction coordinate. In addition, the modespecific rate constant shows a remarkable non-Arrhenius temperature dependence.

Analytical modelling of continuous fibre-reinforced thermoplastics’ thermomechanical properties and implementation into a failure model

Mechanical properties of fibre-reinforced thermoplastics show a remarkable temperature dependence within application temperatures of automotive and aerospace lightweight structures. To take this dependence into account when designing components, the strengths (, , , , ) and stiffnesses (, , , , ) of continuous carbon and glass fibre-reinforced polyamide 6 and glass fibre-reinforced polypropylene are modelled analytically based on experiments. Data from temperature-controlled tests on flat samples in the range from -20 °C to +80 °C are therefore approximated using an extended hyperbolic approach. The models obtained are then evaluated based on their deviation from the experimental values. The main criterion of this evaluation is the reliable prediction of the temperature-dependent material properties while minimising the effort for generating test data and determining model parameters. Furthermore, the failure behaviour of the investigated materials under multiaxial mechanical and thermal stress is examined by implementing the determined strength curves into Cuntze’s physically based failure criterion.

Nuclear spin relaxation rate near the disorder-driven quantum critical point in Weyl fermion systems

Disorder such as impurities and dislocations in Weyl semimetals (SMs) drives a quantum critical point (QCP) where the density of states at the Weyl point gains a non-zero value. Near the QCP, the asymptotic low energy singularities of physical quantities are controlled by the critical exponents $\nu$ and $z$. The nuclear spin-lattice relaxation rate, which originates from the hyperfine coupling between a nuclear spin and long-range orbital currents in Weyl fermion systems, shows intriguing critical behavior. Based on the self-consistent Born approximation for impurities, we study the nuclear spin-lattice relaxation rate $1/T_1$ due to the orbital currents in disordered Weyl SMs. We find that $(T_1T)^{-1}\sim E^{2/z}$ at the QCP where $E$ is the maximum of temperature $T$ and chemical potential $\mu(T)$ relative to the Weyl point. This scaling behavior of $(T_1T)^{-1}$ is also confirmed by the self-consistent $T$-matrix approximation, where a remarkable temperature dependence of $\mu(T)$ could play an important role. We hope these results of $(T_1T)^{-1}$ will serve as an impetus for exploration of the disorder-driven quantum criticality in Weyl materials.

Thermometer of stable SrAl2Si2O8: Ce3+, Tb3+ based on synergistic luminescence

Non-contact optical thermometer appears to be excellent alternative for traditional contact thermometer. Fluorescence intensity ratio (FIR) via thermally-coupled energy levels (TCELs) of one certain lanthanide ion is most adopted method to measure temperature. However, there is an inevitable dilemma in this method that large energy gap (EG) of TCELs is required for gaining highly relative sensitivity (Sr) while small EG is needed for achieving highly absolute sensitivity (Sa). Meanwhile, the EG of TCELs cannot exceed a certain value for achieving thermal equilibrium. To solve this issue, in this work, a new strategy based on synergistic luminescence from Ce3+ and Tb3+ codoped in SrAl2Si2O8 (SASO) has proposed for obtaining highly sensitivity over a wide temperature range. FIR of Ce3+ to Tb3+ in this self-referencing and dual-emitting phosphor shows remarkable contrary temperature dependence and has well fitted linear relationship, owing to resonance energy transfer (ET) from Ce3+ to Tb3+. Meanwhile, the emitting color of the phosphor is gradually shifted from blue to green with temperature, which means it is also potential candidate as colorimetric luminescent thermometer. These results could provide useful inspiration for designing stable and highly sensitive optical thermometer based on ET induced by synergistic luminescence.

Achieving non-degenerate Zn3N2 thin films by near room temperature sputtering deposition

Zn3N2 thin films have been grown at different substrate temperatures by reactive magnetron sputtering in an ultrahigh vacuum chamber. It is demonstrated that low temperature deposition is beneficial for producing nondegenerate Zn3N2 thin films, in stark contrast to previously reported Zn3N2 with high electron concentrations. Elevating the growth temperature will increase the carrier concentration significantly. Analyses of defect concentrations based on the defect formation energies estimated from first-principles calculations indicate that all the native defects are not responsible for the high carrier concentration, whereas unintentional oxygen-on-nitrogen (ON+) and/or hydrogen interstitial (Hi+) defects act as dominant donors in Zn3N2 thin films. Moreover, the remarkable deposition temperature dependence of the carrier concentration in Zn3N2 thin films would be attributed to the Boltzmann distribution of oxygen and/or hydrogen impurities. These results could pave a general way for controlling the carrier concentration in nominally nondoped nitride semiconductors.

Significant Temperature Dependence of the Isosteric Heats of Adsorption of Gases in Zeolites Demonstrated by Experiments and Molecular Simulations

Heat of adsorption is an important factor in determining the utility of a porous material for gas separation and storage applications. Although theoretically the heat of adsorption can depend on temperature, it is common practice to assume that this dependence is so weak that it can be ignored. In this paper, we challenge this common wisdom. We simulated the adsorption isotherms and heats of adsorption of small molecules (CO2, CH4, and N2) in reference siliceous (LTA, CHA, MFI) and cation-exchanged (LTA-4A, Na-LTA Si/Al = 2,5) zeolites and found very significant temperature dependence of the isosteric heat of adsorption for CO2 at low loadings for some systems. In cation-exchanged LTA zeolites, we found more than a 15 kJ/mol decrease over a 300 K range (∼30% variation). We also found remarkable temperature dependence for CO2 in some siliceous zeolites with eight-membered-ring windows (e.g., ITQ-29). A weak temperature dependence was observed for CO2 on silica MFI and for CH4 and N2 adsorption in all mater...

Influence of reactive blending temperature on impact toughness and phase morphologies of PLA ternary blend system containing magnesium ionomer

ABSTRACTIn this study, effects of extrusion temperature on impact toughness and phase morphologies in the reactive poly(lactic acid) (PLA)/epoxy‐containing elastomer (ethylene/n‐butyl acrylate/glycidyl methacrylate [EBA‐GMA]) blend system with magnesium ionomer (magnesium ionomer of ethylene/methacrylic acid copolymer [EMAA‐Mg]), were investigated, and the underlying origin for the dependence of morphology development on reactive blending temperature was analyzed. The extent of reactive compatibilization between PLA/EBA‐GMA and crosslinking of EBA‐GMA initiated by EMAA‐Mg, were determined in terms of Fourier transform infrared spectra of dioxane‐extracted residues, torque rheometer, dynamic mechanical analysis, and gel contents after chloroform extraction. The phase morphologies were studied by electron microscopic observation and dynamic rheological tests. Compared to the ternary blend system containing zinc‐neutralized ionomer of EMAA copolymer (EMAA‐Zn), the ones containing EMAA‐Mg exhibited the less pronounced dependence of notched impact strength on extrusion temperature. With elevating extrusion temperature, the latter ternary blends exhibited different “salami‐like” dispersed phase structure. The morphology development with reactive blending temperature was attributed to the remarkable temperature dependence of crosslinking rate of EBA‐GMA phase initiated by the EMAA‐Mg rather than the difference in the extent of compatibilization. The morphology development mechanism with respect to reactive blending temperature was also discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47682.

Optical properties of Sm3+ and Tb3+ co-doped CaMoO4 phosphor for temperature sensing.

We prepared CaMoO4: x%Sm3+, 5%Tb3+ (x = 0.1, 0.5, 1, 2) phosphors by a precipitation method. Based on the diversity in thermal quenching behavior of different ions in molybdate, a novel thermometry strategy has been proposed. The fluorescence intensity ratio (FIR) of Sm3+ to Tb3+ in these composites exhibits remarkable temperature dependence due to the diverse thermal quenching behaviors of Sm3+ and Tb3+ ions. Excellent temperature sensitivity was achieved from 293 K to 593 K, suggesting that these can perform thermometry. The sensitivities increase with Sm3+ concentration. The maximum sensitivity is as high as 0.312 K-1 (at 593 K) when the Sm3+ concentration is 2%. However, the low Sm3+ concentration sample has a greater relative sensitivity; the maximum value is as high as 0.019 K-1 (at 460 K) when the Sm3+ concentration is 0.1%. Lower Sm3+ concentrations suggested a greater range of luminescent color changes with temperature. Thus, the sample with less Sm3+ can measure temperature via luminescent color.

Double-site emission of Eu2+ ions in Sr4Al14O25: Eu2+ phosphors for self-calibrated optical thermometry

Eu2+ activated aluminate Sr4Al14O25 with dual-emitting centers were prepared via a solid-state method in a reductive atmosphere. Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor along with the lifetimes were characterized, which confirm the 5d→4f energy transition behavior of Eu2+ between 400 nm and 490 nm emission. The fluorescence intensity ratio of I490 and I400 in the phosphors exhibits remarkable temperature dependence, owing to the diverse thermal quenching behaviors of Eu2+ emission centers. Using the phosphors to perform thermometry, excellent temperature sensitivity is achieved in the temperature range of 293–423 K. The maximum absolute and relative sensitivity are 0.004 K-1 and 0.624% at 373 K, respectively. In particular, the dual-site luminescence of Eu2+ ions can be used as the reference signal and the temperature signal of the fluorescence temperature sensor respectively. It will be helpful to develop a new self-reference optical temperature measurement technology with excellent performance.

Cross sections for inelastic 2-to-2 meson-meson scattering in hadronic matter * * National Natural Science Foundation of China (11175111)

With quark-antiquark annihilation and creation in the first Born approximation, we study the reactions: , , , , , , , , , , , and . Unpolarized cross sections for the reactions are obtained from transition amplitudes that are composed of mesonic quark-antiquark relative-motion wave functions and the transition potential for quark-antiquark annihilation and creation. Using a quark-antiquark potential that is equivalent to the transition potential, we prove that the total spin of the two final mesons may not be equal to the total spin of the two initial mesons. Based on flavor matrix elements, cross sections for some isospin channels of reactions can be obtained from other isospin channels of the reactions. Remarkable temperature dependence of the cross sections was observed.

Evolution of mechanical performance with temperature of W/Cu and W/CuCrZr composites for fusion heat sink applications

Power exhaust and materials lifetime have been identified as key challenges for next-generation fusion devices. A water-cooled monoblock divertor, consisting of tungsten as the plasma facing material and copper-based composites as the heat sink, has been proposed as the baseline material. However, there is a large mismatch in the coefficient of thermal expansion and the elastic modulus between these metals, which requires the development of new materials.The goal of this study is the mechanical and microstructural characterization of two composites materials, W-30wt%Cu and W-30wt%CuCrZr, produced using liquid infiltration in an open porous tungsten preform. To reproduce the most adverse in-service conditions, materials were characterized under high vacuum atmosphere up to 800°C. From the measured mechanical properties, a remarkable temperature dependence can be assessed, since it is noticeable that for both materials, tensile and flexural strength equally decrease as the measurement temperature increases. However, the fracture behavior of W-30CuCrZr is on average 25% higher than that of W-30Cu (21MPam1/2 versus 17MPam1/2 at RT) although this gap is narrower at higher temperatures; at 800°C, the contribution of the Cu-based phase is quite low, thus fracture is primary controlled by the W initial skeleton. From these values, it can be inferred that the yield strength and fracture toughness of W-30CuCrZr composite are superior, whilst it presented lower elastic modulus and rupture strain values than the W-30Cu composite.As a result, the metal matrix composites presented in this article could effectively dissipate heat while overcoming the thermal stresses produced during operation, since a decent thermomechanical performance was observed at relevant reactor temperatures. This is of vital importance to enhance the performance, life cycle, and reliability of the component.

Charmonium dissociation in collisions with ϕ mesons in hadronic matter**Supported by National Natural Science Foundation of China (11175111)

The ϕ-charmonium dissociation reactions in hadronic matter are studied. Unpolarised cross sections for , or , , , or , , or and are calculated in the Born approximation, in the quark-interchange mechanism and with a temperature-dependent quark potential. The potential leads to remarkable temperature dependence of the cross sections. With the cross sections and the ϕ distribution function we calculate the dissociation rates of the charmonia in interactions with the ϕ meson in hadronic matter. The dependence of the rates on temperature and charmonium momentum is relevant to the influence of ϕ mesons on charmonium suppression.

Effect of Water Coordination on Luminescent Properties of Pyrazine-Bridged Dinuclear Cu(I) Complexes.

Two luminescent pyrazine-bridged dinuclear Cu(I) complexes, namely, [{Cu(PPh3)2(H2O)}(μ-MeOpyz){Cu(PPh3)2(CH3CN)}](BF4)2 and [{Cu(PPh3)2(H2O)}(μ-MeOpyz){Cu(PPh3)2(H2O)}](BF4)2 (H2O-Cu2-AN and H2O-Cu2-H2O; PPh3 = triphenylphosphine, MeOpyz = 2-methoxypyrazine), were successfully synthesized and characterized by single-crystal X-ray diffraction and luminescence measurements. X-ray analysis revealed that the water molecules are coordinated to both Cu(I) ions to form almost the same P2N1O1 coordination structure in H2O-Cu2-H2O, whereas one of the two Cu ions in H2O-Cu2-AN was coordinated by acetonitrile instead of water to form a different P2N2 coordination environment. The asymmetric H2O-Cu2-AN exhibits very bright yellow-green emission with a high emission quantum yield (λem = 550 nm, Φ = 0.70) at room temperature in the solid state in spite of the coordination of water molecule, which usually tends to deactivate the emissive state through O-H vibration. The intense emission at room temperature is a result of thermally activated delayed fluorescence, and the remarkable temperature dependence of emission lifetimes indicates the existence of unique multiple emission states for the asymmetric dinuclear complex. In contrast, the emission of H2O-Cu2-H2O was observed at longer wavelengths with remarkably a lower quantum yield (λem = 580 nm, Φ = 0.05). Time-dependent density functional theory calculations suggested that the emission could result from the metal-to-ligand charge-transfer transition state. However, it could be rapidly deactivated by the structural distortion around the Cu ion with a less-bulky coordination environment in H2O-Cu2-H2O.