Strong Temperature Dependence Research Articles

Spectral engineering and thermometric performance of LiIn(Si2-xGex)O6: Cr3+ phosphor for multi-mode NIR thermometry

Exploring the phosphors with tunable NIR emission to realize versatile application is highly desired while remains a challenging. Herein, we show that the composition modification of Si/Ge ratio in LiIn(Si2-xGex)O6: Cr3+ could lead to a precise tuning of Cr3+ emission wavelength in 840–900 nm range with significant emission enhancement. The spectral engineering is quantitatively analyzed on the base of structural variation and crystal fielding parameters, revealing that the PL tuning is originated from reducing crystal field by Ge4+-induced lattice expansion. It is found that the strong temperature-dependence of Cr3+ emission enables it to read the temperature in three ways: variation of peak wavelength, fluorescence intensity and decay lifetime variation. All modes exhibit good linear response with R2 > 0.99 in range of 293–473 K. The ability to absorb and emit in NIR-I biological window allows it to be used as a thermometer in deep tissue temperature sensing and imaging. All results indicate that this phosphor is of great potential in NIR thermometry application.

Reduction of Temperature Sensitivity for Resonant Micro-Pressure Sensor Using Glass-Silicon Coupling Wafer Packaging

This article presents a resonant micro-pressure sensor consisted of the resonators positioned on device layer of SOI wafer, which was vacuum packaged by a glass-silicon coupling wafer. Ambient pressure under measurement deflected the pressure-sensitive diaphragm, inducing intrinsic frequency shift of resonators, while the glass-silicon coupling wafer packaging can alleviate the side effect of environmental temperature disturbance, reducing shifts of intrinsic frequency of resonators. Numerical simulations were employed to the design and optimization of sensor where technical issues correlated with strong temperature dependence and improper mechanical coupling were addressed. The developed sensor was fabricated based on conventional microfabrication processes, and characterized with comparison to the counterpart using glass wafer packaging. Characterization results revealed that the temperature sensitivities were quantified as 37.93 Hz/°C vs. 10.36 Hz/°C in the full temperature (−40 °C to 85 °C) range with corresponding eigenfrequency shifts measured as 13.18 Hz vs. 3.75 Hz after 20 temperature cycles, respectively, for the sensors using glass vs. glass-silicon coupling wafer packaging. Meanwhile, under the condition of room temperature with pressure of 10 kPa, 1kPa, and 0.05 kPa, the long-term measurement deviations of sensors over 90 days period were reduced from12.17±2 Pa to3.24±1 Pa with the help of glass-silicon coupling wafer packaging. These results validated that the developed sensor using glass-silicon coupling wafer packaging may be an effective tool in the field of micro-pressure measurements.

Effect of co substitution of (Y, Mn) on electrical properties of bismuth ferrite

Using the method of solid-state reaction technique, (Y, Mn) modified Bismuth ferrite ferroelectric ceramic Bi0.8Y0.2(Fe0.5Mn0.5)O3 is prepared. The room temperature XRD analysis confirms the formation of a new single-phase compound with an orthorhombic crystal structure. The electrical properties are analyzed by the impedance analyzer. Through analysis, the dielectric behavior of the compound is explored in broad temperature and frequency span, which shows the strong temperature & frequency dependence characteristics of the compound. The high transition temperature of the parent bismuth ferrite compound (∼830 °C) markedly reduces to 370 °C when Y is substituted at A site and Mn at B site. Temperature-dependent behavior of conductivity and activation energy values estimated in different regimes are calculated from the temperature-dependent ac conductivity graphs, which suggests that the conduction process is of mixed type (i.e. ionic-polaronic and space charge generated from the oxygen ion vacancies). The ac conductivity spectrum obeys Jonscher’s universal power law.

Size and temperature-dependent stability of polarization vortex in PbTiO3 nanosheet under uniaxial tension or compression

ABSTRACT The stability of polarization vortex is absolutely crucial to the service performance of promising ferroelectric storage devices. Some phase field simulations were conducted on the PbTiO3 nanosheets with an initial polarization vortex under uniaxial tension or compression to investigate the conditions and types of vortex instability as well as the effects of the nanosheet size and temperature on them. The instability of polarization vortex has strong size and temperature dependence. The critical tensile stress decreases with increasing nanosheet size, and only the α-type vortex instability is observed in tensile nanosheets. However, the critical compressive stress first increases and then decreases with increasing nanosheet size, and there exists a peak size. The β-type (including β1 and β2-type) instability occurs when the nanosheet size is less than the peak size, but the α-type instability occurs when the nanosheet size is larger than the peak size. An elevated temperature reduces the critical tensile and compressive stresses, but increases the peak size. These are very important for design of promising nano-ferroelectric devices as high density memories.

First-principles calculations to investigate elastic and thermodynamic properties of FeAlNixCrMn quinternary alloys

In this study, the structural stability, elastic properties, and thermodynamic properties of FeAlNixCrMn high-entropy alloys (HEAs) (x = 0, 0.25, 0.5, and 0.75) were systematically studied. The analysis of the total density of states and Debye temperature of FeAlNixCrMn shows that the structural stability of the alloy first increased and then decreased with the increasing of Ni content. According to the elastic constant, the influence of Ni content on the elastic modulus, toughness, brittleness, and elastic anisotropy of FeAlNixCrMn was analyzed. Finally, it is found that the thermal expansion coefficient and heat capacity show shows a strong temperature dependence only at low temperature. Furthermore, the dependence of temperature on the Grüneisen parameter is just the opposite of that of the Debye temperature. This study provides a reference and theoretical guidance for the design and performance prediction of HEAs components.

Osmium(IV) pyrophosphate: Synthesis, Crystallization, and Ligand‐Field Analysis of the [OsIVO6] Chromophore

AbstractTwo polymorphs of burgundy‐red OsP2O7, with cubic (ZrP2O7 structure type, Z=4, a=7.8276(4) Å, 3×3×3 superstructure with a’=3a=23.484(2) Å) and triclinic symmetry (ruby‐red crystals, single‐crystal X‐ray structure determination, GeP2O7 structure type, (no. 2), Z=2, a=4.8072(7) Å, b=6.8993(13) Å, c=8.050(1) Å, α=91.82(2)°, β=92.92(1)°, γ=107.42(2)°, 98 parameters, R1=0.045, wR2=0.144, 3006 unique reflections with |Fo|>4σ(Fo)) have been obtained reducing OsO4 by phosphorus in sealed silica ampoules followed by subsequent chemical vapour transport. Reaction with the wall led to mixed SiIV/OsIV silicophosphates (Os1−xSix)3[Si2O(PO4)6] {x=0.84, pale orange, SiIV3[Si2O(PO4)6] structure type, , Z=3, a=7.893(1) Å, c=24.409(5) Å, 59 parameters, R1=0.058, wR2=0.160, 1311 unique reflections with 1033 |Fo|>4σ(Fo); x=0.47, orange, GeIV3[Si2O(PO4)6] structure type, , Z=2, a=7.9979(3) Å, c=16.4625(5) Å, 59 parameters, R1=0.040, wR2=0.094, 902 unique reflections with 749 |Fo|>4σ(Fo)}. Both structures were refined from single‐crystal data. Above 25 K triclinic OsP2O7 shows temperature independent paramagnetism with a strong temperature dependence of pointing to as electronic ground state for Os4+ (d4) with strong spin‐orbit coupling leading to =0 and the non‐magnetic ground state of the octahedral [OsIVO6] chromophore.. Optical spectra of both polymorphs of OsP2O7 show similar combinations of intense sharp and broad absorption bands typical for dn electronic systems systems with both, spin‐orbit coupling and ligand field splitting, being strong. The observations are consistent with the ligand‐field parameters Δo=20000 cm−1, B=704 cm−1, and ζ=3454 cm−1 for the octahedral [OsIVO6] chromophore.

Probabilistic impacts of compound dry and hot events on global gross primary production

As the basis of food and fiber production, gross primary production (GPP) plays a critical role in the growth of vegetation. Understanding the response of GPP to climate extremes is important for ensuring food security under ongoing global warming. Plenty of evidence shows that the recent widespread dry or hot events across the globe have significant influences on GPP, yet little is known about their joint impacts. Here, we reveal a high risk of compound dry and hot events globally, in response to the strong negative dependence of precipitation and temperature, which leads to a substantial negative impact on GPP for both crop and pasture ecosystems. Using a meta-Gaussian model, we show that the probability of a reduction in global terrestrial GPP increases significantly under compound dry and hot conditions relative to their individual counterparts. Further, the risk of GPP reductions increases with the intensified severity of compound dry and hot events across the globe. These results unravel the sensitivity of GPP to compound dry and hot conditions and highlight the need to account for the influence of compound events when assessing the carbon budget.

Dysprosium Substituted Ce:YIG Thin Films for Temperature Insensitive Integrated Optical Isolator Applications.

Magneto-optical isolators are key components in photonic systems. Despite the progress of silicon-integrated optical isolators, the Faraday rotation of silicon-integrated magneto-optical materials, such as cerium-doped yttrium iron garnet (Ce:YIG), show a strong temperature dependence, limiting the temperature range for integrated nonreciprocal photonic device applications. In this work, we report dysprosium substituted Ce:YIG thin films (Dy2Ce1Fe5O12, Dy:CeIG) showing a low temperature coefficient of Faraday rotation. A temperature insensitive range of the Faraday rotation is observed in between 25 °C to 70 °C for this material, compared to 20% variation of the Faraday rotation in Ce:YIG thin films. A Dy:CeIG based temperature insensitive silicon-integrated optical isolator operating in the temperature range of 23 °C to 70 °C is experimentally demonstrated.

Separation of SO2 and NO2 with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO2 Dimerization Effect.

NO2 and SO2, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO2 and SO2 is a key process step to enable practical deployment. This work proposes SO2 separation from NO2 using chabazite zeolite (SSZ-13) membranes and provides insights into the feasibility and advantages of this process using molecular simulation. Grand canonical ensemble Monte Carlo and equilibrium molecular dynamics methods were respectively adopted to simulate the adsorption equilibria and diffusion of SO2, NO2, and N2O4 on SSZ-13 at varying Si/Al (1, 5, 11, 71, +∞), temperatures (248-348 K), and pressures (0-100 kPa). The adsorption capacity and affinity (SO2 > N2O4 > NO2) demonstrated strong competitive adsorption of SO2 based on dual-site interactions and significant reduction in NO2 adsorption due to dimerization in the ternary gas mixture. The simulated order of diffusivity (NO2 > SO2 > N2O4) on SSZ-13 demonstrated rapid transport of NO2, strong temperature dependence of SO2 diffusion, and the impermeability of SSZ-13 to N2O4. The membrane permeability of each component was simulated, rendering a SO2/NO2 membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO2-N2O4 dimerization in molecular sieving of SO2 from NO2 was addressed, providing a facile membrane separation strategy at room temperature.

Temperature dependence of the Gilbert damping of La0.7Sr0.3MnO3 thin films

Due to its half metallic nature, ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ is an attractive highly correlated electronic system to obtain ultralow magnetic damping. In this paper we analyze the temperature and thickness dependence of the damping of the magnetization dynamic of epitaxial thin ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ films. Our analysis reveals that the damping encompasses resistivelike and conductivelike contributions, as in transition metal ferromagnets. The data also show a large increase of the ferromagnetic resonance linewidth at low temperature, a feature that we ascribe to the presence of a dead layer, insulating and magnetically active, that behaves like a spin sink. The associated spin-pumping term shows a strong temperature dependence, linked to that of the spin mixing conductance. By clarifying some unexplored aspects of spin dynamics in half-metallic manganites, our results contribute to the progress in the burgeoning field of oxide spin orbitronics.

Water Limitation in Forest Soils Regulates the Increase in Weathering Rates under Climate Change

Climate change is generally expected to have a positive effect on weathering rates, due to the strong temperature dependence of the weathering process. Important feedback mechanisms such as changes in soil moisture, tree growth and organic matter decomposition can affect the response of weathering rates to climate change. In this study, the dynamic forest ecosystem model ForSAFE, with mechanistic descriptions of tree growth, organic matter decomposition, weathering, hydrology and ion exchange processes, is used to investigate the effects of future climate scenarios on base cation weathering rates. In total, 544 productive coniferous forest sites from the Swedish National Forest Inventory are modelled, and differences in weathering responses to changes in climate from two Global Climate Models are investigated. The study shows that weathering rates at the simulated sites are likely to increase, but not to the extent predicted by a direct response to elevated air temperatures. Besides the result that increases in soil temperatures are less evident than those in air temperature, the study shows that soil moisture availability has a strong potential to limit the expected response to increased temperature. While changes in annual precipitation may not indicate further risk for more severe water deficits, seasonal differences show a clear difference between winters and summers. Taking into account the seasonal variation, the study shows that reduced soil water availability in the summer seasons will strongly limit the expected gain in weathering associated with higher temperatures.

High‐quality ternary relaxor ferroelectric thin films on Si substrates by pulsed laser deposition method

AbstractIn this work, ternary relaxor ferroelectric thin films 0.5mol% Mn‐doped 0.36Pb(In1/2Nb1/2)O3‐0.36Pb(Mg1/3Nb2/3)O3‐0.28PbTiO3 (Mn‐PIMNT) with high Curie point were grown on the Pt/Ti/SiO2/Si substrate with the addition of La0.6Sr0.4CoO3 (LSCO) as a buffer layer. The phase and domain structure, nanoscale piezoelectric response, and macroscopic ferroelectric, dielectric, pyroelectric properties of Mn‐PIMNT thin films were studied. Both the crystalline quality and the crystallographic orientation exhibited strong temperature dependence within the substrate temperature of 450–580°C. Under the optimized temperature of 530°C, the Mn‐PIMNT thin film exhibited excellent global electrical properties with remnant polarization Pr∼35.6 μC/cm2, coercive field Ec∼5.1 kV/mm, dielectric constant ∼3360, and relatively low dielectric loss tanδ∼0.03. It was further found that the pyroelectric coefficient of the Si‐substrated Mn‐PIMNT thin film reached 6.7 × 10−4 C/m2·K. The optimized ferroelectric thin films Mn‐PIMNT on Si substrate with excellent temperature stability show great potential in integrated microelectromechanical systems.

Complete deciphering of the dynamic stereostructures of a single aggregation-induced emission molecule

<h2>Summary</h2> The realization of functional molecular devices is inseparable from deep understanding of the intrinsic structure-property relationship of molecules. However, due to limited detection sensitivity and temporal resolution of current methods, there are rare reports on fully probing <i>in situ</i> dynamic changes of the molecular stereostructures at the single-molecule level in real time. Here, we present a complete deciphering of the dynamic stereostructures of a single aggregation-induced emission molecule using molecular junctions, which are capable of executing rapid real-time electrical measurements to achieve the unprecedented electrical mapping, thus feeding back the dynamic changes of the molecular stereostructures. Experimental and theoretical investigation consistently verify the intramolecular motions under electric field and the isomerization dynamics with strong temperature and electric field dependence, offering new insights into the development of ultra-sensitive devices. We anticipate that further integration of optical measurements with this approach will enable sophisticated synchronous monitoring of broad single-molecule photochemistry and photophysics.

Impedance spectroscopic study of charge transport and relaxation mechanism in the lead-free hybrid perovskite CH3NH3CuCl3

In the field of commercialization, organic–inorganic hybrid perovskite materials are becoming more popular these days in view of their prospective use in solar cells and also in other optoelectronic applications. In this paper, a non-toxic CH3NH3CuCl3 (MACuCl3) hybrid perovskite is successfully synthesized via the slow evaporation solution growth technique. The monoclinic phase of the material is checked using the X-ray diffraction measurement. The chemical composition of the prepared compound is discussed by a scanning transmission electron microscope coupled with the energy dispersive X-ray spectroscopy (STEM-EDS). Such systematic characterizations as differential scanning calorimetry (DSC) measurements and dielectric measurements indicate that MACuCl3 goes through a reversible phase transition at T1 ≈ 350/352 K MACuCl3 demonstrates a semiconducting property with a direct band gap value of approximately 2.54 eV. Over the 10−1-106 Hz frequency range, the dielectric constant, the loss factor, the electric modulus and also the electrical conductivity of MACuCl3 show strong temperature dependence. The Nyquist plot confirms the various contributions of grains and grain boundaries to the total impedance. In the high-frequency region, the dielectric constant tends to increase with temperature. The modified Cole–Cole plot asserts that while the relaxation time decreases with the rise in temperature, the space charge and free charge conductivity increase the moment the temperature climbs. In accordance with the modified Kohlrausch-Williams-Watts (KWW) equation, an asymmetrical nature corresponding to the non-Debye type of the perovskite is noticed in the electric modulus spectra at different temperatures. Moreover, the imaginary part of the electric modulus spectra is found to shift from the non-Debye toward the Debye type with the increase in temperature despite not getting the exact Debye response and emerging as a semi-conductor material. The study of the charge transfer mechanism of MACuCl3 is carried out based on Elliott's theory. The conduction mechanism in MACuCl3 is interpreted through the following two approaches: the overlapping large polaron tunneling (OLPT) model (phase 1) and the non-overlapping small polaron tunneling (NSPT) model (phase 2). Moreover, the high dielectric constant of MACuCl3 which is associated with a low dielectric loss makes it a possible candidate for energy harvesting devices.

The Impact of Long-Term Memory Effects on the Linearizability of GaN HEMT-Based Power Amplifiers

This article presents how the emission time constant of deep-level traps is responsible for the achievable linearity (linearizability) degradation of gallium nitride high electron mobility transistor (GaN HEMT)-based power amplifiers. It is shown that the worst case scenario happens when the emission rate is on the order of the signal bandwidth, with substantial improvement when they begin to differ. Moreover, because of the strong temperature dependence of the emission time constant, self-heating is shown to play a major role in that linearizability degradation. To demonstrate the importance of the coupling of these two effects (electrothermal and trapping), two GaN HEMT dies with the same structure but different trap activation energies (which dictate the impact of temperature on trapping) were used. Digital predistortion tests using long-term evolution-like signals showed that these devices present different adjacent channel power ratios and normalized mean squared errors, after linearization with the same procedure, which varied with the signal bandwidth as theoretically predicted.

Temperature dependence of inertial pumping in microchannels

Inertial pumping is a promising new method of moving fluids through microchannels but many of its properties remain unexplored. In this work, inertial flow rates are investigated for different channel lengths, operating temperatures, and resistor pulse energies. The flow in closed channels is visualized by adding fluorescent tracer beads to the test fluid (pure water). A robust methodology of extracting flow rates from high-resolution video recordings is developed. Flow rates are found to scale inversely with the channel length. The observed dependence is explained based on a simple phenomenological “kick” model of inertial pumping. Flow rates are also fitted to the more fundamental one-dimensional model of inertial pumping from which the intrinsic drive bubble strength is extracted. The measured flow rates vary strongly with temperature. For well-developed drive bubbles, flow rates at T=70 °C are about 12× higher than at T = 30 °C. Three separate effects contribute to increasing flow rates at high temperatures: (i) lower viscosity of the test fluid, (ii) a stronger drive bubble, and (iii) increasing mechanical efficiency of the pump, i.e., better conversion of the drive bubble strength to unidirectional post-collapse kick. Relative contributions of the three effects are quantified. The energy dependence of flow rates exhibits a clear saturation behavior. The bubble strength is fitted to a phenomenological saturation model. In the end, a complete predictive length-temperature-energy model of flow rates is constructed. The observed strong temperature dependence of inertial pumping should be considered when designing microfluidic workflows. It also highlights the need for integrated flowmeters that could stabilize complex flow patterns via sensory feedback.

A temperature dependent extreme value analysis of UK surface ozone, 1980–2019

Elevated surface ozone during heatwaves and recent hot summers raises concerns over the potential for climate change to exacerbate ozone air pollution in the UK. In this paper, we perform a robust statistical analysis of four decades worth of daily maximum 8-h (MDA8) ozone measurements from the UK's Automated Urban and Rural Network. A temperature dependent extreme value model is developed to characterise the magnitude and frequency of extreme ozone events and to determine probabilities for ozone exceeding health thresholds, as defined in the UK's air quality index. Our model is found to describe the tails of the MDA8 ozone distributions well at all 119 monitoring sites considered. For the decade 2010–2019, we estimate that >90% of sites have a 1-year MDA8 ozone return level greater than the ‘moderate’ ozone threshold of 100 μg/m3. We also find that 33% of sites are currently expected to breach the UK government's national air quality objective that MDA8 ozone should not exceed 100 μg/m3 more than ten times per year. We estimate the present overall probability of MDA8 ozone exceeding 100 μg/m3 on a given day to be between <0.1% and 5.4%, depending on site, with averages of 2.7% (rural) and 1.6% (urban background locations). Our analysis reveals a significant decline over time in the likelihood of the UK experiencing extreme ozone episodes, with 1-year return levels in the 1980s now roughly comparable to 10-year return levels in the present. Similarly, probabilities of MDA8 ozone exceeding 100 μg/m3 have decreased by a factor of ∼2–6 since the 1980s in some locations. However, our results also highlight a strong positive temperature dependence to the risk of ozone exceedances. In consequence, increasingly hot summers due to climate change may offset some of these gains.

Estimation of Staphylococcus aureus growth rates from CO2 with absorption spectroscopy

AbstractIt is very important to monitor and evaluate the growth of Staphylococcus aureus (S. aureus) under various conditions. However, so far there is no technology that can monitor S. aureus in real time. This work proves that the wavelength modulated absorption spectroscopy (WMAS) based on tunable diode lasers can quickly measure the concentration of carbon dioxide produced by microorganisms. We use a variety of fitting models to get the growth curves of S. aureus and calculated the relationship between the growth rate and time through the obtained growth curve. Using the proposed technology, we have studied the growth status of S. aureus at different temperatures (five points in the range of 26–43°C), and the results show that the maximum growth rate have a strong temperature dependence. Therefore, it is proved that WMAS monitoring S. aureus is a user‐friendly, non‐invasive, fast, and high signal‐to‐noise ratio technology, which can be used for rapid and accurate bacterial growth assessment in the industry.

Scratch-Healing Behavior of Ice by Local Sublimation and Condensation.

We show that the surface of ice is scratch healing: micrometer-deep scratches in the ice surface spontaneously disappear by thermal relaxation on the time scale of roughly an hour. Following the dynamics and comparing it to different mass transfer mechanisms, we find that sublimation from and condensation onto the ice surface is the dominant scratch-healing mechanism. The scratch-healing kinetics shows a strong temperature dependence, following an Arrhenius behavior with an activation energy of ΔE = 58.6 ± 4.6 kJ/mol, agreeing with the proposed sublimation mechanism and at odds with surface diffusion or fluid flow or evaporation–condensation from a quasi-liquid layer.

On the conformational equilibria between isobutyl halide (CH3)2CH–CH2X (X=Cl, Br and I) rotational isomers: A combined ultrasonic relaxation spectroscopic and computational study

In this study, ultrasonic relaxation spectroscopy and molecular orbital calculations have been used to investigate the rotational-isomeric equilibria in isobutyl halide (CH3)2CH–CH2X (X = Cl, Br and I) liquids as a function of frequency and temperature under isobaric conditions. The sound absorption in the a/f2 representation appeared to deviate from straight line with frequency in the MHz region revealing a single Debye-type relaxation process, which is attributed to thermal relaxation of a rotational isomeric equilibrium for all isobutyl halide systems. From the temperature dependence of the relaxation parameters, the associated thermodynamic parameters and the respective volume changes were estimated for each liquid and discussed in view of the outcome of density functional theory electronic structure calculations. The activation enthalpy was found to be strongly dependent on the ionic radius of the halide. Furthermore, the lower energy state of all isobutyl halide systems is two-fold degenerate. The experimental results indicate that a shear viscosity relaxation is questionable in the frequency region covered in this work. The observed-to-classical absorption ratio α/αcl and the volume-to-shear viscosity ratio nV/ns have been evaluated and used as a measure to monitor the strength of the intermolecular bonding. The values and the strong temperature dependence of these ratios are typical of a relaxation process associated to rotational isomers equilibrium. The results have been discussed in the context of inter- and intra-molecular interactions.