Temperature Dependence Of Density Research Articles

Synthesis and electrical transport properties of superconducting platinum silicide thin films and devices

We evaluate the material characteristics of superconducting platinum silicide (PtSi) thin films as candidate materials for superconducting quantum information devices compatible with silicon technology. These films were synthesized using magnetron sputtering under ultrahigh vacuum conditions, followed by rapid thermal annealing. Polycrystalline PtSi films synthesized by this method have the favorable properties of superconducting critical temperature of 0.95 K and relatively long zero-temperature Ginzburg-Landau coherence length of 76 nm. We further studied coplanar microbridge devices fabricated by electron beam lithography and chlorine-free reactive ion etching, finding that the temperature-dependent critical current density follows the Ginzburg Landau depairing mechanism.

Variable density and heat generation impact on chemically reactive carreau nanofluid heat-mass transfer over stretching sheet with convective heat condition

The present study focuses on the physical significance of heat generation and chemical reaction on Carreau nanofluid with convective heat conditions. Heat transfer is characterized using convective boundary conditions. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) by using well define stream functions and similarity transformations. Using a shooting methodology, the Keller-box method with Newton Raphson scheme is used to elaborate the numerical solutions of physical phenomena. Utilizing a similar technique to find the impact of physical parameter such as the production of heat δ, the rate of reaction Λ, Biot numbers γ, Brownian motion variable Nb, the thermophoresis parameters Nt, the Weissenberg quantity We, Prandtl number Pr, and Lewis number Le on velocity profile, temperature profile and mass transmission profile are determined graphically. The skin-friction coefficient −f″(0), local Nusselt −θ′(0), and Sherwood numbers −ϕ′(0) are analyzed numerically. Increment in fluid velocity and slip temperature are depicted with high Biot number. Maximum magnitude of fluid temperature and fluid concentration function are depicted at high value of temperature dependent density. The magnitude of heat and mass transportation enhanced with maximum choice of Brownian motion.

Analysis of pyroelectric properties in quenched NBT-BT composition

Quenching has recently demonstrated its efficacy in elevating the ferroelectric to relaxor phase transition temperature (TFR) in 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT). Consequently, the current investigation comprehensively examines the pyroelectric properties of quenched NBT-6BT. The pyroelectric coefficient is measured using the Byer-Roundy method, incorporating a strategic approach to mitigate the risk of overestimation by implementing cyclic heating and cooling. Quenching enhances the depolarization temperature (Td) by approximately 40 °C, quantified through the temperature-dependent pyroelectric current density (Ip). The maximum pyroelectric current (52nA) and voltage (200V) responses to thermal cycling (15s heating/cooling) were observed in quenched NBT-6BT. The voltage sensitivity figures of merit were equivalent for both furnace-cooled and quenched NBT-6BT. The assessment of pyroelectric energy storage involved charging a 48 nF capacitor in 180s, resulting in a maximum voltage of 38V. The outcomes strongly endorse the quenched NBT-6BT as an efficient pyroelectric material, showcasing promising attributes for applications in sensing and energy harvesting across a broad temperature range.

Analysis of activation energy, chemical reaction, and variable density on magnetically driven heat transportation: Applications in nanofluid lubrication and machining

The importance of this investigation is to examine the heat and mass transportation of magneto nanofluid movement along a heated sheet with exponential temperature-dependent density, entropy optimization, thermal buoyancy, activation energy, and chemical reaction aspects. The influence of these factors in cutting tools by means of machining and nanofluid lubrication is a significant process in cutting zone, chip cleaning, lubricating, and cooling productivity in milling. The corresponding energy activation and chemical process are essential to understand the thermal behavior of nanofluid. The appropriate transformations are used to solve nonlinear partial differential equations within the framework of ordinary differential equations using stream functions and similarity variables. The Keller box method is employed to efficiently solve these equations computationally under the Newton–Raphson approach. Through tables and figures, the fluid velocity, temperature distribution, and concentration consequences are sketched using various controlling parameters. It is seen that the fluid temperature function increases with noticeable amplitude as the Eckert factor, variable density, chemical-reaction, and activation energy increase. It is found that the noticeable enhancement in heat and mass transportation is deduced for maximum Brownian motion and thermophoresis. This work is important in various applications such as cutting fluids, drilling, brake oil, engine oil, minimum quantity lubrication, enhanced oil recovery, and controlled friction between the tool-chip and tool-work during machining operations.

Robustly Boosting Thermoelectric Performance of N-Type PbSe via Lattice Plainification and Dynamic Doping.

Ideal thermoelectrics shall possess a high average ZT, which relies on high carrier mobility and appropriate carrier density at operating temperature. However, conventional doping usually results in a temperature-independent carrier concentration, making performance optimization over a wide temperature range be challenging. This work demonstrates the combination of lattice plainification and dynamic doping strategies is an effective route to boost the average ZT of N-type PbSe. Because Sn and Pb have similar ionic radii and electronegativity, this allows Sn to fill the intrinsic Pb vacancies and effectively improves the carrier mobility of PbSe to 1300 cm2 V-1 s-1. Furthermore, a trace amount of Cu is introduced into the Sn-filled PbSe to optimize the carrier concentration. The extra Cu is situated in the interstitial sides of the lattice, which undergoes a dissolution-precipitation process with temperature, leading to a strongly temperature-dependent carrier density in the material. This dynamic doping effectively improves the electrical transport properties and is also valid to suppress the lattice thermal conductivity. Ultimately, the resulting PbSn0.004Se+3‰Cu obtains a maximum ZT of ≈1.7 at 800 K and an average ZT of ≈1.0, with a 7.7% power generation efficiency in a single-arm device, showing significant potential for commercial application.

In Situ Fabrication of Highly Efficient and Stable Cs2NaInCl6: Sb3+@PVDF Composite Films for Optoelectronic Devices.

Lead-free double perovskites (DPs) have superior phase stability and optical properties, which make them competitive for future applications in illumination and displays. However, the preparation of DPs was mainly based on high-temperature heating and hydrochloric acid as a solvent to form powders, which increased the risk and cost of the preparation process and limited its further application. In this study, the growth of Cs2NaInCl6: Sb3+ DPs in polyvinylidene difluoride (PVDF) films was achieved using an in situ fabrication strategy with DMSO as the solvent. The prepared Cs2NaInCl6: Sb3+@PVDF composite films (CFs) can achieve a bright blue emission under 302 nm irradiation. To achieve the optimal luminescent performance of CFs, the photoluminescence (PL) intensity of Cs2NaInCl6: Sb3+@PVDF CFs under various in situ preparation conditions was compared. In addition, the photoluminescence quantum yield (PLQY) of CFs was increased from 0.72% to 83.77% by adjusting the doping amount of Sb3+, and the fluorescence lifetimes t1 and t2 were 131.08 and 1048.52 ns, respectively. Temperature-dependent PL spectroscopy and density functional theory (DFT) calculations indicate that these excellent optical properties are derived from the self-trapped excitons (STEs) at the [SbCl6]3- octahedron and [InCl6]3- octahedron connected via Cl-Na-Cl. The CFs also demonstrated excellent environmental stability, maintaining a relatively stable PL intensity even under conditions of water immersion, high temperatures, and ultraviolet (UV) radiation. Finally, we used the CFs to assemble a blue light-emitting device (LED), which showed good and stable blue emission performance at different currents. This work can provide a new idea for preparing DPs, which is conducive to promoting their commercial application in high-performance optoelectronic devices.

Quantum migration and its local heat impact: Understanding local heat capacity of confined systems.

For noninteracting particles confined in a constant volume, the temperature derivative of the local energy assumes negative values in thermodynamic equilibrium at low temperatures. This peculiar behavior may entail the misleading unphysical conclusion that the local heat capacity is negative. However, we show that temperature-dependent density variations of confined particles induce an energy selective particle transport within the domain, here called temperature-induced quantum migration. This macroscopic quantum phenomenon causes a redistribution of local heat and ensures a non-negative local heat capacity. Moreover, it induces local heating and cooling effects and a massive overshoot in local heat capacity. The quantum migration also builds up the thermal part of confinement energy, manifesting in an excess global heat capacity. Analyzing the local energy fluctuations shows that the linear relationship between heat capacity and fluctuations is broken at the local scale.

Subdiffusive and superdiffusive phonon transport induced significant thermal rectification across a one-dimensional Kapitza interface

Anomalous heat conduction in low dimensional materials shows divergent thermal conductivity with increasing characteristic length, which brings many opportunities in thermal management applications and unexplored phonon transport mechanisms. The molecular heterojunctions, consisting of an interface that is formed by different lattices, exhibit unique physical properties especially thermal rectification phenomenon. In this work, we investigate the heat conduction across a one-dimensional heterojunction bridging a carbon nanotube (CNT) and a boron nitride nanotube (BNNT). The molecular dynamic (MD) simulation shows that the rectification ratio is as high as 8.9 in a 300-nm system at/above the room temperature, which is due to the asymmetric interfacial thermal conductance in the opposite directions of heat flow. The interfacial thermal conductance (G) obeys the length dependence of G ∝ Lβ, presenting a divergent and convergent behaviors of anomalous heat conduction that was only reported for homogeneous materials. By analyzing the length-dependent and temperature-dependent phonon density of state, this anomalous interfacial heat conduction can be explained by the Kapitza resistance model and the population of frequency-dependent phonons. Further calculation of mean square displacement of atoms validates the superdiffusion and subdiffusion behavior of the interfacial conductance. This result demonstrates the superb capability of the one-dimensional heterojunction to control phonon transport, which could be used as the basic element of high-efficient and intelligent thermal management devices.

Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 : a theoretical and experimental study

Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni3In2Se2kagome topological semimetal. First-principles calculations of the band structure without the inclusion of spin-orbit coupling (SOC) shows that three bands are crossing the Fermi level (EF), indicating the semi-metallic nature. With SOC, the band structure reveals a gap opening of the order of 10 meV.Z2index calculations suggest the topologically nontrivial natures (ν0;ν1ν2ν3) = (1;111) both without and with SOC. Our detailed calculations also indicate six endless Dirac nodal lines and two nodal rings with aπ-Berry phase in the absence of SOC. The temperature-dependent resistivity is dominated by two scattering mechanisms:s-dinterband scattering occurs below 50 K, while electron-phonon (e-p) scattering is observed above 50 K. The magnetoresistance (MR) curve aligns with the theory of extended Kohler's rule, suggesting multiple scattering origins and temperature-dependent carrier densities. A maximum MR of 120% at 2 K and 9 T, with a maximum estimated mobility of approximately 3000 cm2V-1s-1are observed. Ni3In2Se2is an electron-hole compensated topological semimetal, as we have carrier density of electron (ne) and hole (nh) arene≈nh, estimated from Hall effect data fitted to a two-band model. Consequently, there is an increase in the mobility of electrons and holes, leading to a higher carrier mobility and a comparatively higher MR. The quantum interference effect leading to the two dimensional (2D) weak antilocalization effect (-σxx∝ln(B)) manifests as the diffusion of nodal line fermions in the 2D poloidal plane and the associated encircling Berry flux of nodal-line fermions.

Improvement of optical properties of lead-free double perovskite Cs2AgInCl6 nanocrystals through Bi ion alloying

Lead-free double perovskite nanocrystals (NCs) have garnered significant attention due to their non-toxicity and excellent stability, offering vast potential applications in the field of optoelectronics. They are considered promising substitutes for lead-based perovskite NCs. Herein, we successfully synthesized monodisperse, uniformly sized, cubic-shaped Cs2AgIn1-xBixCl6 (0 ≤ x ≤ 1) NCs via a simple hot injection approach. The Cs2AgInCl6 NCs exhibit a lower photoluminescence quantum yield (PLQY) of 3.9 % due to the presence of parity-forbidden transitions. However, with the introduction of Bi3+ alloying, the parity-forbidden transitions are broken, transforming into direct transitions allowed by parity. This transformation leads to efficient bright yellow emission, with the highest PLQY reaching up to 31.6 % (Cs2AgIn0.90Bi0.10Cl6 NCs). Adjusting the Bi3+ alloying concentration allows tuning the NCs band gap from 3.62 eV to 2.88 eV, and the exciton lifetime can be extended from 5.99 ns to 24.88 ns. Temperature-dependent photoluminescence spectra and density functional theory calculations indicate that Bi3+ alloying increases the exciton binding energy, weakens the electron-phonon coupling, and breaks parity-forbidden transitions. Moreover, Cs2AgIn0.90Bi0.10Cl6 NCs display outstanding stability under ambient conditions, laying a solid foundation for their applications in optoelectronics. The results of this study open a new pathway to enhance the optical performance of lead-free double perovskite nanomaterials.

Interstitials in Thermoelectrics.

Defect structure is pivotal in advancing thermoelectric performance with interstitials being widely recognized for their remarkable roles in optimizing both phonon and electron transport properties. Diverse interstitial atoms are identified in previous works according to their distinct roles and can be classified into rattling interstitial, decoupling interstitial, interlayer interstitial, dynamic interstitial, and liquid interstitial. Specifically, rattling interstitial can cause phonon resonance in cage compound to scatter phonon transport; decoupling interstitial can contribute to phonon blocking and electron transport due to their significantly different mean free paths; interlayer interstitial can facilitate out-of-layer electron transport in layered compounds; dynamic interstitial can tune temperature-dependent carrier density and optimize electrical transport properties at wide temperatures; liquid interstitial could improve the carrier mobility at homogeneous dispersion state. All of these interstitials have positive impact on thermoelectric performance by adjusting transport parameters. This perspective therefore intends to provide a thorough overview of advances in interstitial strategy and highlight their significance for optimizing thermoelectric parameters. Finally, the profound potential for extending interstitial strategy to various other thermoelectric systems is discussed and some future directions in thermoelectric material are also outlined.

Characterization and Application of Cyrene as a Biomass-Based Solvent for Homogeneous Heck-Coupling Reaction.

Cyrene, a renewable, non-toxic substance having negligible vapor pressure, even at high temperatures, was proposed as a reaction medium for homogeneous Pd-catalyzed Heck-coupling reactions. It was first characterized by its temperature-dependent physicochemical properties, i.e., vapor pressure, density, surface tension, heat capacity, and viscosity, the key parameters of its reaction and process chemistry. Its refractive indices in the function of temperature were also determined. Hereafter, the effect of reaction parameters (Pd source, nature of the base, the water content of the reaction mixture, leaving group (-I, -Br, -Cl, and -OTf of aromatic substrates) on Pd-catalyzed Heck-coupling reaction was investigated using iodobenzene and styrene as model substrates. Subsequently, 4-substituted iodobenzene and styrene derivatives were applied to investigate the effect of electronic parameters on the reaction efficiency and functional group tolerance. To demonstrate the applicability of the system, thirteen stilbene derivatives were isolated with good to high yields and purity (> 95%) using 0.2 mol% of Pd, 1.5 eq. of Et3N as a base, in 1 mL of Cyrene for 2 h at 100 °C.

Influence of temperature-dependent density inhomogeneity on the stability of atmospheric stratified fluids

The stability of atmospheric stratified fluids is revisited to study the influence of the temperature-dependent density inhomogeneity due to thermal expansion in the Earth’s lower atmosphere (with heights 0 to 50 km) under the action of gravity. Previous theory in the literature [Phys. Lett. A 480 (2023) 128 990] is modified and advanced. It is found that the Brunt-Väisälä frequency associated with internal gravity waves is modified, leading to new instability conditions of vertically stratified fluids. The possibility of the onset of Rayleigh-Bénard convective instability is also discussed, and the influences of the modified Brunt-Väisälä frequency and the density and temperature gradients on the instability growth rates are studied.

Estimation of the Hazardous Chemical Leakage Scale Inside Buildings Using CFD

Increased industrialization and aging infrastructure have resulted in leaks of hazardous chemicals, such as CO. Leak modeling is crucial to developing emergency response strategies. Therefore, we simulated the time to criticality (TTC), which is the time to reach the threshold limit for occupational exposure, of a CO leak. The basis of the study is a fire dynamics simulator, a computational fluid dynamics model that was used to investigate the movement of CO in various scenarios, including using different building layouts and areas, temperatures, and leak diameters. Multiple regression analysis was performed to obtain regression equations for the TTC as a function of the independent variables. Ultimately, we found that the type of dispersion varies with respect to the temperature-dependent density of CO, and, among the independent variables, the leak diameter had the strongest effect on the TTC. The regression equations with logarithmic conversion were validated and found to have higher accuracy than those without logarithmic conversion. The findings provide useful information for developing emergency response plans regarding leak size in the case of hazardous chemical leakage. However, empirical studies of different gas types and leakage scenarios are required.

Managing temperature in open quantum systems strongly coupled with structured environments.

In non-perturbative non-Markovian open quantum systems, reaching either low temperatures with the hierarchical equations of motion (HEOM) or high temperatures with the Thermalized Time Evolving Density Operator with Orthogonal Polynomials Algorithm (T-TEDOPA) formalism in Hilbert space remains challenging. We compare different ways of modeling the environment. Sampling the Fourier transform of the bath correlation function, also called temperature dependent spectral density, proves to be very effective. T-TEDOPA [Tamascelli et al., Phys. Rev. Lett. 123, 090402 (2019)] uses a linear chain of oscillators with positive and negative frequencies, while HEOM is based on the complex poles of an optimized rational decomposition of the temperature dependent spectral density [Xu et al., Phys. Rev. Lett. 129, 230601 (2022)]. Resorting to the poles of the temperature independent spectral density and of the Bose function separately is an alternative when the problem due to the huge number of Bose poles at low temperatures is circumvented. Two examples illustrate the effectiveness of the HEOM and T-TEDOPA approaches: a benchmark pure dephasing case and a two-bath model simulating the dynamics of excited electronic states coupled through a conical intersection. We show the efficiency of T-TEDOPA to simulate dynamics at a finite temperature by using either continuous spectral densities or only all the intramolecular oscillators of a linear vibronic model calibrated from abinitio data of a phenylene ethynylene dimer.

New analysis of the temperature-dependent threshold density for electron self-trapping in gaseous helium.

We present the results of a new analysis of the literature data on electron mobility μ in dense helium gas aimed at determining the existence of a threshold density for electron self-trapping in gaseous helium as a function of temperature. We have investigated the density dependence of μ and, when available, its dependence on the electric field. The experimental data are favorably rationalized by minimizing the excess free energy of the self-localized states within the optimum fluctuation model. It is shown that the formation of electron bubbles via the self-trapping phenomenon is determined by the delicate balance between the electron thermal energy, the density dependence of the electron energy at the bottom of the conduction band in the gas, and the work necessary to expand the bubble. We show that the self-trapping phenomenon is not limited to low temperatures but occurs at any temperatures for large enough densities.

A neural-network potential for aluminum

Aluminum and its alloys are most often used as structural materials due to their specific properties, such as low weight, low energy consumption for remelting and the possibility of almost complete processing. This paper utilizes machine learning, specifically the Behler-Parrinello neural network scheme, to develop a powerful potential for studying the underlying mechanisms of deformation, fracture, and defect formation. By surpassing the limitations of first principles calculations, the application of machine-learned potentials (MLP) becomes highly advantageous for describing pure aluminum (Al) in its solid and liquid phases. Specifically, from the generated potential equilibrium, thermodynamic, elastic, and vibrational properties of face-centered cubic (fcc) Al are obtained in very good agreement especially with density functional theory (DFT) results as well as with previous calculations using existing semi-empirical potentials, such as EAM and MEAM, recent machine-learned potentials, and experimental data. Furthermore, our potential proves to accurately reproduce defect formation energies such as previously computed and measured stacking-fault energy curves. Finally, stacking fault profiles as well as key quantities of the liquid phase such as the melting point at ambient pressure, temperature-dependent densities, and radial distribution functions are also calculated in very good agreement with the results from previous theoretical and experimental investigations. Nevertheless, our investigation goes beyond previous studies in proving excellent agreement with experimental data especially of the specific heat and the melting point at very high pressures. The competitive analysis performed in this work thus clearly demonstrates the validity and accuracy of the generated machine-learned potential to describe a wide range of properties of Al at various temperatures and pressures and thereby lays ground for future applications.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

Computational analysis of thermal performance of temperature dependent density and Arrhenius-activation energy of chemically reacting nanofluid along polymer porous sheet in high temperature differences

An innovative technique to improve heat transmission is the use of nanofluids. Nanofluids have a significant thermal conductivity for better heat transport. For the thermal behavior of a porous polymer sheet, activation energy assessment is a useful technique for the advancement of the thermal properties of polymers. The governing model is developed for the numerical and physical analysis of heat transfer of porous polymer sheets. The present model is converted into a smooth format for the accuracy of results. The Keller box and Newton–Raphson approaches are used to calculate the thermal properties numerically. The novelty of this research is the depiction of the temperature distributions and heat transfer of chemically reacting thermophoretic nanomaterials along porous polymer stretching sheets. It is noted that the velocity and temperature of thermophoretic nanoparticles decreases and nanoparticle concentration increases as activation energy increases. It is noted that the velocity of nanoparticles increases and concentration decreases as the temperature difference increases. The enhanced heating transfer with maximum thermophoretic transportation was depicted under maximum reaction and activation energy. It is observed that the mass transfer of nanomaterials increases as the Brownian motion of thermophoretic nanomaterials enhances.

A unified theory of the self-similar supersonic Marshak wave problem

We present a systematic study of the similarity solutions for the Marshak wave problem in the local thermodynamic equilibrium (LTE) diffusion approximation and in the supersonic regime. Self-similar solutions exist for a temporal power law surface temperature drive and a material model with power law temperature dependent opacity and energy density. The properties of the solutions in both linear and nonlinear conduction regimes are studied as a function of the temporal drive, opacity, and energy density exponents. We show that there exists a range of the temporal exponent for which the total energy in the system decreases, and the solution has a local maxima. For nonlinear conduction, we specify the conditions on the opacity and energy density exponents under which the heat front is linear or even flat and does possess its common sharp characteristic; this characteristic is independent of the drive exponent. We specify the values of the temporal exponents for which analytical solutions exist and employ the Hammer–Rosen perturbation theory to obtain highly accurate approximate solutions, which are parameterized using only two numerically fitted quantities. The solutions are used to construct a set of benchmarks for supersonic LTE radiative heat transfer, including some with unusual and interesting properties such as local maxima and non-sharp fronts. The solutions are compared in detail to implicit Monte Carlo and discrete-ordinate transport simulations as well gray diffusion simulations, showing a good agreement, which highlights their usefulness as a verification test problem for radiative transfer simulations.