Temperature-dependent Behavior Research Articles

Prediction of temperature-dependent mechanical behavior of metals based on thermodynamic strength and deformation theory

Prediction of temperature-dependent mechanical behavior of metals based on thermodynamic strength and deformation theory

Cholesteric liquid crystal mixtures for the switchable smart windows and light shutters: Electro-optical and dielectric behaviour

Abstract Cholesteric liquid crystal (CLC) mixtures with variable pitch lengths were prepared for the electrical switchable smart window and light shutter applications by taking varied concentrations (2.6, 3.0, 4.0, and 5.0 wt%) of chiral dopant (R1011) having helical twisting power (HTP) 37.6 μm−1 and nematic E7 liquid crystal (LC). The morphological and electro-optical analysis of these CLC mixtures filled in 10µm thick cells were observed and reported herein, the switching of initial planar (P) and initial focal conic (FC) to homeotropic (H) states as well as vice-versa. The operating voltage of the 2.6 wt% of chiral doped CLC cell was relatively lower among all the sample cells compared with other concentrations. The maximum contrast ratio (CR) was observed for 5.0 wt% chiral doped CLC cell with initial planar state. However, the best CR was observed in 2.6wt% CLC cell with initial FC state. The comparative macroscopic views of the P, FC, and H states in the OFF and ON conditions of applied voltage for prepared CLC cells were observed for transparent and opaque states. Further, UV-visible spectroscopy was performed in the P, FC, and H states under the application of an externally applied field to observe the absorbance and band gap behavior of the fabricated CLC cells. Additionally, chiral concentration-dependent dielectric parameters with variable frequency in initial P and FC states of the fabricated cells were also reported. The temperature-dependent phase behavior of all the prepared cells exhibited a slight decrease in the isotropic phase of LC due to the doping of chiral dopants.

High-Temperature Optoelectronic Transport Behavior of n-TiO2 Nanoball-Stick/p-Lightly Boron-Doped Diamond Heterojunction.

The n-TiO2 nanoballs-sticks (TiO2 NBSs) were successfully deposited on p-lightly boron-doped diamond (LBDD) substrates by the hydrothermal method. The temperature-dependent optoelectronic properties and carrier transport behavior of the n-TiO2 NBS/p-LBDD heterojunction were investigated. The photoluminescence (PL) of the heterojunction detected four distinct emission peaks at 402 nm, 410 nm, 429 nm, and 456 nm that have the potential to be applied in white-green light-emitting devices. The results of the I-V characteristic of the heterojunction exhibited excellent rectification characteristics and good thermal stability at all temperatures (RT-200 °C). The forward bias current increases gradually with the increase in external temperature. The temperature of 150 °C is ideal for the heterojunction to exhibit the best electrical performance with minimum turn-on voltage (0.4 V), the highest forward bias current (0.295 A ± 0.103 mA), and the largest rectification ratio (16.39 ± 0.005). It is transformed into a backward diode at 200 °C, which is attributed to a large number of carriers tunneling from the valence band (VB) of TiO2 to the conduction band (CB) of LBDD, forming an obvious reverse rectification effect. The carrier tunneling mechanism at different temperatures and voltages is analyzed in detail based on the schematic energy band structure and semiconductor theoretical model.

Thermocontrolled Radical Nucleophilicity vs Radicophilicity in Regiodivergent C-H Functionalization.

The temperature-dependent switching behavior of the saccharin radical is demonstrated, enabling the regiodivergent C3-H and C7-H functionalization of quinoxalin-2(1H)-ones. The saccharin radical was generated through N-Br bond cleavage in N-bromosaccharin (NBSA) and was observed to transition between radical and radicophile roles. At -10 °C, it was utilized as a radicophile, resulting in 100% C3-amination, while at +35 °C, it acted as a radical, leading to exclusive C7-bromination. Radical nucleophilicity was controlled by temperature modulation.

Nonconventional Full-Color Luminescent Polyurethanes: Luminescence Mechanism at the Molecular Orbital Level.

The study of structure-activity relationships is a top priority in the development of nontraditional luminescent materials. In this work, nonconjugated polyurethanes (PUs) with full-color emission (red, green, and blue) are easily obtained by control of the diol monomer structure and the polymerization conditions. Selected diol monomers introduced single, double, or triple bond repeating units into the main chain of the PUs, in order to understand how unsaturated bonds and H-bonds affect their luminescence from a molecular orbital viewpoint. Detailed experimental and theoretical results show that the PUs have different temperature-dependent behaviors related to the interplay of H-bonding, through-space n-π interactions, and aggregation properties. The potential applications of PUs in colorful displays, covert information transmission, and multifunctional bioimaging have been verified. This work provides a new general protocol for the simple preparation of multifunctional nonconventional fluorescent polymers and deepens the understanding of their luminescence mechanisms.

Temperature-dependent deformation behavior of dual-phase medium-entropy alloy: In-situ neutron diffraction study

Temperature-dependent deformation behavior of dual-phase medium-entropy alloy: In-situ neutron diffraction study

Comprehensive Study on Thermal Variability of 50/70 Bitumen: An Examination of Fatigue Testing Outcomes

The primary methodology for this research involves conducting a series of fatigue tests on 50/70 bitumen to assess its behaviour under varying thermal conditions. The tests will be carried out using a Dynamic Shear Rheometer (DSR), a widely used apparatus in bitumen testing. The DSR allows for measuring bitumen's rheological properties, such as viscosity and elasticity, under controlled temperature and stress conditions. The 50/70 bitumen samples will be carefully prepared according to standard testing procedures to ensure uniformity. The bitumen will be heated to a specified temperature for testing, and samples will be taken at different thermal conditions to simulate varying environmental scenarios. The bitumen samples will be placed in the DSR and subjected to cyclic loading to simulate the stresses experienced in real-world road conditions. The tests will be conducted at a range of temperatures, typically from low temperatures (to simulate cold weather) to high temperatures (to simulate hot weather). This will allow for the study of the temperature-dependent behaviour of bitumen. The DSR will measure the *complex shear modulus (G)**, which provides information on the stiffness of the material, and the phase angle (δ), which reflects the material’s ability to recover after deformation. These parameters are crucial for assessing the fatigue resistance of bitumen. The fatigue behaviour of the bitumen will be evaluated under repeated loading conditions. The dynamic shear rheometer will apply cyclical stress to the bitumen samples and measure the resulting strain. The number of cycles to failure, defined by a significant decrease in stiffness or an increase in phase angle, will be recorded. The focus will be on understanding how the fatigue resistance of the bitumen is affected by temperature fluctuations. By subjecting the bitumen to these varying conditions, it will be possible to determine at which. Temperatures the material exhibits optimal durability or fails prematurely.

A high-dimensional neural network potential for Co3O4

The Co3O4spinel is an important material in oxidation catalysis. Its properties under catalytic conditions, i.e. at finite temperatures, can be studied by molecular dynamics simulations, which critically depend on an accurate description of the atomic interactions. Due to the high complexity of Co3O4, which is related to the presence of multiple oxidation states of the cobalt ions, to dateab initiomethods have been essentially the only way to reliably capture the underlying potential energy surface, while more efficient atomistic potentials are very challenging to construct. Consequently, the accessible length and time scales of computer simulations of systems containing Co3O4are still severely limited. Rapid advances in the development of modern machine learning potentials (MLPs) trained on electronic structure data now make it possible to bridge this gap. In this work, we employ a high-dimensional neural network potential (HDNNP) to construct a MLP for bulk Co3O4spinel based on density functional theory calculations. After a careful validation of the potential, we compute various structural, vibrational, and dynamical properties of the Co3O4spinel with a particular focus on its temperature-dependent behavior, including the thermal expansion coefficient.

Effect of Temperature on Electrochemical Behavior of Cobalt Diselenide Ternary Composite-based Supercapacitor

The electrochemical behavior of a cobalt diselenide (CoSe₂)-based ternary composite for hybrid supercapacitor applications across varying temperatures has been studied. To get advanced electrochemical results composite was synthesized by incorporating activated carbon and cellulose fibers with CoSe₂ (the optimization of the ternary composite is depicted in our other research paper). A series of electrochemical analyses was directed at different temperatures to assess the temperature-dependent behavior of the supercapacitor. The results demonstrate that the ternary composite exhibits enhanced electrochemical properties, with a high specific capacitance at 40˚C temperatures due to improved ion mobility and charge transfer kinetics. At 40°C, the composite-based cell revealed a specific capacitance of 248 F g⁻¹, which further decreased at higher temperatures, showcasing a negative correlation between temperature and electrochemical performance. The energy and power densities obtained for the same are 22 Wh kg-1 and 411 W kg-1. The findings suggest that such hybrid supercapacitors could play a dynamic part in energy storage technologies.

Numerical Simulation of the Frequency Dependence of Fatigue Failure for a Viscoelastic Medium Considering Internal Heat Generation.

Accurately predicting fatigue failure in CFRP laminates requires an understanding of the cyclic behavior of their resin matrix, which plays a crucial role in the materials' overall performance. This study focuses on the temperature elevation during the cyclic loadings of the resin, driven by inelastic deformations that increase the dissipated energy. At low loading frequencies, the dissipated energy is effectively released as heat, preventing significant temperature rise and maintaining a consistent, balanced thermal state. However, at higher frequencies, the rate of energy dissipation exceeds the system's ability to release heat, causing temperature accumulation and accelerating damage progression. To address this issue, the study incorporates non-recoverable strain into a fatigue simulation framework, enabling the accurate modeling of the temperature-dependent fatigue behavior. At 0.1 Hz, damage accumulates rapidly due to significant inelastic deformation per cycle. As the frequency increases to around 2 Hz, the number of cycles until failure rises, indicating reduced damage per cycle. Beyond 2 Hz, higher frequencies result in accelerated temperature rises and damage progression. These findings emphasize the strong link between the loading frequency, non-recoverable strain, and temperature elevation, providing a robust tool for analyzing resin behavior. This approach represents an advancement in simulating the fatigue behavior of resin across a range of frequencies, offering insights for more reliable fatigue life predictions.

Investigation of the temperature-dependent functioning of BiFeO3 as a ferroelectric material through X-ray diffraction analysis

In recent years, Bismuth Ferrite (BiFeO3, BFO) has emerged as a promising multiferroic material due to its high antiferromagnetic Néel temperature (TN ~ 623–643 K) and ferroelectric Curie temperature (TC ~ 1083–1103 K). These properties make BFO a strong candidate for exhibiting a magnetoelectric effect even at room temperature. Understanding the temperature-dependent ferroelectric behavior of BFO is crucial for optimizing its performance in applications where stable ferroelectric behavior at operational temperatures is essential for enhancing device efficiency, stability, and functionality. This study investigates the impact of temperature on the crystallographic characteristics (unit cell type, bond lengths, and dimensions) and ferroelectric performance of BFO. X-ray diffraction and electrical hysteresis measurements confirm the presence of a ferroelectric phase with a rhombohedral R3c structure, along with two phase transitions: the first around 600 K from ferroelectric to paraelectric, and the second near 1050 K from paraelectric back to ferroelectric.

Extremely Large Anisotropy of Effective Gilbert Damping in Half-Metallic CrO2.

Half-metals are a class of quantum materials with 100% spin polarization at the Fermi level and have attracted a lot of attention for future spintronic device applications. CrO2 is one of the most promising half-metal candidates for which the electrical and magnetic properties have been intensively studied in the last several decades. Here, we report the observation of a giant anisotropy (∼1600%) of effective Gilbert damping in the single-crystalline half-metallic (100)-CrO2 thin films, which is significantly larger than the values observed on conventional ferromagnetic Fe and CoFe thin films. Furthermore, the effective Gilbert damping exhibits opposite temperature-dependent behaviors below 50 K with magnetic field along the [010] direction and near the [001] direction. These experimental results suggest the strong spin-orbit coupling anisotropy of the half-metallic CrO2 and might pave the way for future magnonic computing applications.

Temperature-dependent optical and surface electrical properties of Pb(Zr0.3Ti0.7)O3 /p-GaN film

Understanding the temperature-dependent optical and electrical properties of PZT, a multifunctional ferroelectric thin film with temperature sensitivity, is crucial for its applications. This study systematically investigated the microstructure, optical, and surface electrical features of Pb(Zr0.3Ti0.7)O3 thin film deposited on p-GaN substrate (PZT/p-GaN), with an emphasis on their response to temperature variations. Band gap energy (3.643 eV) and the three interband electronic transitions (3.528 eV, 4.662 eV, 6.582 eV) were extracted from optical measurements, which govern the photoelectron transmission behavior of the PZT/p-GaN. Additionally, we identify three phase-transition temperatures (450 K, 550 K, and 620 K) through temperature-dependent optical behavior analysis. With increasing temperature, the electronic transitions and bandgap show a redshift trend, and the bandgap change follows the O'Donnell equation with a significant electron-phonon coupling coefficient (S = 10.284), revealing a strong electron-phonon coupling effect in PZT/p-GaN. The temperature-dependent kelvin piezoelectric force microscopy (KPFM) shows that the surface potential and work function of PZT/p-GaN exhibit different linear variations over three temperature ranges divided by the phase transition temperature point as a demarcation. Furthermore, we observed that the optical and surface electrical properties exhibit anomalous trends at the phase transition point. These findings offer a theoretical reference for the application of PZT thin films in optoelectronics and electronic devices.

Anomalous Relaxation Behaviour in La0.7Sr0.3MnO3 (LSMO)-ZnO Nanocomposite

Abstract The temperature-dependent relaxation behaviour and the conduction mechanism in LSMO-ZnO nanocomposite have been studied by employing complex impedance spectroscopic techniques. The imaginary part of impedance exhibits a relaxation phenomenon, with the relaxation frequency showing a Gaussian-like dependence on temperature. At temperatures below 340 K the relaxation frequency increases with increase in temperature due to the reduction in grain and grain boundary resistances. However, an unusual decreasing nature of relaxation frequency with increase in temperature, above 358 K, is observed. This feature is explained in terms of an increased value of the grain boundary capacitance owing to a transition from bipolaron hopping to single polaron hopping. Such anomalous relaxation behavior makes the nanocomposite a suitable candidate for applications in sensors, switches, actuators etc. The dispersion behavior of the AC conductivity is explained with Jonscher’s law involving small polarons. The study confirms that the correlated barrier hopping (CBH) is the dominant dynamic process involved in the AC conduction mechanism in LSMO-ZnO nanocomposite across the measured range of temperature.

Temperature-dependent electrical behaviour of pulsed laser deposited CH3NH3PbBr3 thin films for visible wavelength photodetection

Temperature-dependent electrical behaviour of pulsed laser deposited CH3NH3PbBr3 thin films for visible wavelength photodetection

Analytical model to characterize temperature-dependent anisotropic-asymmetric behavior of Mg-Gd-Y alloy

Analytical model to characterize temperature-dependent anisotropic-asymmetric behavior of Mg-Gd-Y alloy

Temperature-dependent mechanical behavior in a novel hierarchical B2-strengthened high entropy alloy: Microscopic deformation mechanism and yield strength prediction

Integration of twinning and hierarchical microstructure into a face-centered cubic (FCC) matrix is a novel research approach for advancing high-temperature alloys, enhancing strength without the need for costly heavy elements. Here, a three-level B2 phase was incorporated into a NiCoCrFe high-entropy alloy (HEA) matrix, offering a high strengthening effect at room temperature and a good resistance to moderate-temperature softening while preserving the low stacking fault energy of the FCC matrix. The resulting NiCoCrFeAl0.3Si0.3 HEA exhibited stable yield strength, strain hardening, and deformation twinning over a broad temperature ranging from 77 to 973 K. By establishing a yield strength model based on the various strengthening mechanisms, the study highlighted the important role of the three-level B2 phase in the exceptional mechanical properties of the alloy across a wide temperature range. These findings present a promising avenue for the advancement of high-temperature structural materials.

A slope-based J-integral approach and advanced image processing for assessment of the cyclic fatigue delamination behavior of adhesive joints

A fatigue fracture mechanics methodology was developed and established, employing a slope-based J-integral approach combined with advanced image processing techniques. Adhesively bonded double cantilever beam (DCB) specimens were tested under constant displacement amplitude loading. The beam rotation was tracked by affixing a repetitive pattern on the DCB specimens and capturing images at the maximum displacement amplitude. Using a custom-developed image processing procedure, the beam rotation was deduced. To validate the methodology, DCB fatigue experiments were conducted at 23, 60 and 75 °C on aluminum adherends bonded with a structural 2-K epoxy adhesive. The J-based approach was compared with a conventional, compliance-based linear elastic fracture mechanics (LEFM) method. The epoxy was a rather brittle, high-modulus adhesive with a bond line thickness of 0.25 mm, resulting in predominantly linear elastic material behavior. By analyzing the images taken during fatigue testing, a stiffening effect of the steel load blocks was observed. Excluding pattern elements directly below the load block yielded the best agreement between J-integral and LEFM data. Both approaches were in excellent agreement within the investigated temperature range. The investigated adhesive exhibited a highly temperature-dependent behavior, which was associated with higher crack propagation rates and a lower fatigue threshold at 60 and 75 °C.

Simultaneous Entropic Coefficient Measurement and Multi-Species, Multi-Reaction Modelling

The multi-species, multi-reaction (MSMR) model is developed through the fitting of pseudo-open circuit voltage (POCV) data acquired by cycling a cell at a sufficiently low rate (C/50).1 By comparing MSMR fitted data taken at various temperatures, both temperature dependence of fitting parameters and thermodynamic data including the state-of-charge (SOC) dependent entropic coefficient (dU/dT), entropy (ΔS), and enthalpy (ΔH) can be gleaned.2 In this presentation, POCV behavior of coal-derived graphite will be discussed and compared to thermodynamic measurements of lithium-intercalation under potentiostatic testing conditions.3 Simultaneously measuring POCV data and determining thermodynamic parameters has the advantages of minimizing testing time and complexity. The MSMR model’s ability to distinguish minute changes in temperature dependent active material behavior will be highlighted through a comparison of coal-derived graphite and commercially available synthetic graphite.4 Implications of thermodynamic parameters and temperature dependent behavior on cell and pack level engineering will also be presented.

Thickness-dependent structural and growth evolution in relation to dielectric relaxation behavior and correlated barrier hopping conduction mechanism in Ni0.5Co0.5Fe2O4 ferrite thin films

Ferrite thin films are explored due to their promising properties, which are essential in various advanced electronic devices. However, depositing a film with pure phase and uniform microstructure is challenging. The Ni0.5Co0.5Fe2O4ferrite thin films are deposited using pulsed laser deposition technique to explore the effect of thickness on structural properties, growth evolution, temperature-dependent dielectric behavior, and conduction mechanisms. Microstructural analysis revealed that the films are uniformly grown, exhibiting surface roughness ranging from ∼2 to 4 nm. The dielectric response, adhering to a modified Debye model, exhibited multiple relaxation processes, with notable changes in the dielectric constant and loss as film thickness increased. Impedance spectra exhibited both space charge and dipolar relaxation phenomena, corroborated by Cole-Cole and electrical modulus plots. The analysis of the imaginary electric modulus using the Kohlrausch-Williams-Watts function revealed non-Debye-type relaxation in all deposited films, characterized by thermally activated broad peaks. Conductivity decreased up to a certain film thickness, and the frequency exponent derived from Jonscher's power law suggested a correlated barrier hopping model for AC conduction. Activation energies improved with film thickness up to 125 nm, consistent with a constant energy barrier for polarons during relaxation and conduction phases. The film with 125 nm thickness exhibited the optimal dielectric properties, with the maximum dielectric constant, minimum dielectric loss, and highest activation energy. These findings highlight the potential of dense, uniformly grown films with high dielectric constants and low dielectric losses for advanced electronic device applications.