Temperature Dependence Of Characteristics Research Articles

Record-High Thermoelectric Performance in Al-Doped ZnO via Anderson Localization of Band Edge States.

Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco-friendly constituting elements. Here, adopting a unique synthesis route via chemical co-precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics ( 21.5µW cm-1 K-2 and 0.5 at 1100K in ) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi-dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnOthermoelectrics.

Transient Heat Transfer Analysis in Metal Plates with Variable Thickness

Nonlinear transient heat transfer via conduction–radiation is a dynamic topic of long-standing interest with applications ranging from aeronautical and mechanical engineering to industrial and civil security. To gain a better understanding of the performances of materials having thermal proprieties that change during nonlinear heat transfer, several studies using the finite element method (FEM) have been conducted. Such studies apply nonlinear thermal material characteristics to describe the complete system under different loading conditions in each region by adjusting the temperature values for the other three edges and the thickness parameter with Dirichlet boundary conditions. As a result, while modeling and simulating temperature distributions for such situations, nonlinearities generated by temperature-dependent thermal conductivity must be considered. In this work, we focus on the analysis of coupled transient heat transfer through two metal plates with temperature-dependent thermal characteristics in which the temperature is fixed along the bottom edge and heat is transferred from both the top and bottom faces of the two plates. FEM is employed to solve the nonlinear heat equation and compute the temperature as a function of time for variable thickness. The study examines the effect of modifying the thickness parameter values on the temperature distribution over time for various edge values over 5,000 s.

Molecular dynamics exploration of the temperature-dependent elastic, mechanical, and anisotropic properties of hcp ruthenium

Molecular dynamics calculations were performed for the hitherto unclarified temperature-dependent elastic, mechanical, and anisotropic properties of the hexagonal closed pack (hcp) ruthenium (Ru) between 0 and 1200 K. All elastic stiffness constants were found to decrease with increasing temperature. Under the examined temperature range, hcp Ru obeys Born stability conditions. Further, both Pugh ratio analyses and calculated Poisson ratio values mutually suggest the brittle character of hcp Ru between 0 and 1200 K. The intricate hardness behavior of hcp Ru was also obtained and discussed throughout the work. For the considered temperature range, hcp Ru exhibits apparent elastic anisotropy that exponentially increases with increasing temperature. Moreover, presently obtained ground state (T = 0 K and P = 0 GPa) theoretical data for hcp Ru agree well with the former experimental and theoretical data. The present findings on the temperature-dependent characteristics of this metal may further inspire future applied works.Graphical abstract

DFT study of mechanical, optoelectronic, and thermoelectric characteristics of double perovskites Li2CuTiZ6 (Z = Cl, Br, I) for energy harvesting technology

Recent studies have produced stable inorganic perovskites that contain no lead, replacing lead-containing perovskites' risky and unstable properties. The present investigation thoroughly examined the electrical behavior, elastic characteristics, optical features, and transport properties of Li2CuTlZ6 (Z = Cl, Br, I) halides in order to discover potential applications. The Wien2k code was utilized to apply density functional theory (DFT) in order to clarify these physical properties. Using the generalized gradient approximation (PBEsol-GGA), we determined structural parameters through the energy optimization procedure that corresponded with the available data. Additionally, elastic parameters as well as formation energies ranging between -2.33 to -1.39 eV were used to validate cubic durability for the two halides. Moreover, the modified Becke-Johnson (mBJ) potential successfully provided precise direct bandgap values for all halides. According to this study, the shift in anions from Cl to Br is responsible for the reduction in band gap within the infrared spectrum. Our computed optical parameter findings show that Li2CuTlCl6 and Li2CuTlBr6 halides demonstrate excellent optoelectronic efficiency with low reflection, strong optical absorption, and conductivity. The investigation clarifies that the temperature-dependent character of the materials electrical transport properties is due to their very small bandgap. These materials may find use in thermoelectric applications, as evidenced by the almost unity of the obtained figure of merit, which points to their semiconducting behaviour.

Exploring Shannon entropy and heat capacity of doped GaAs quantum dot under the influence of noise

Present enquiry explores the Shannon entropy and the corresponding heat capacity of GaAsquantum dot (QD) which is doped with Gaussian impurity and under the aegis of Gaussian white noise (GWHN). GWHN may take additive and multiplicative routes for its entrance to the doped QDs. The enquiry analyzes the features of temperature-dependence of above thermodynamic properties and also the effect of various physical parameters on them at a given temperature. The study reveals some kind of complex interplay involving the temperature zone, presence/absence of GWHN, mode of application of GWHN and the particular physical parameter concerned which ultimately shapes the profiles of entropy and heat capacity. Often, the study reveals competitive behavior between thermal disorder and spatial disorder which noticeably affects the said thermal properties. Moreover, the study also highlights some unusual behavior in the entropy profiles only under multiplicative noise of high noise strength.

Temperature Dependency of Photoelectronic Properties of Group III-V Arsenide Solar Cell

This study explores the effect of temperature on different characteristics of Solar Cells (SC) composed of a structured III-V arsenide group. The temperature dependence of the SC characteristics was investigated numerically and by simulation. In both approaches, each characteristic was compared with a conventional Si SC. InAs showed superior stability and lower temperature sensitivity, as it has a negligible decrease of 0.098 eV in the energy bandgap, while the energy bandgaps of Si, AlAs, and GaAs are 0.129, 0.186, and 0.200 eV, respectively. Moreover, with a decay rate of 81.911 mV/°K, InAs exhibited the lowest temperature sensitivity in open-circuit voltage. InAs additionally demonstrated the least increase in degradation rate, while the SC power output is still a cause of concern. AlAs, Si, and GaAs had a total accumulative gradient change of 0.162, 0.136, and 0.034% in the degradation rate, respectively, while InAs showcased the highest stability by displaying a change of only 0.008%. A comparative analysis illustrated that among these III-V arsenide compounds, InAs had a rock-bottom sensitivity to temperature changes and better temperature stability in both numerical and simulation approaches.

Influence of prior austenite grain size on martensite-austenite islands morphology and decomposition characteristics during two-step tempering in Mn-Ni-Mo steel

Martensite-austenite (M/A) islands are typical in the quenched microstructure of Mn-Ni-Mo steel, frequently utilized for fabricating reactor pressure vessels (RPV). These islands can decompose into harmful long rod-shaped Fe3C carbides during tempering above 600°C, quantifying the negative effect of M/A island decomposition on mechanical properties and indicating a potential issue in RPV fabrication. To address this issue, the present study investigates a two-step tempering process on three different prior austenite grain size (PAGS) specimens (5 µm, 47 µm, and 119 µm). The effect of PAGS on M/A island decomposition characteristics during sub-600°C tempering and their impact on precipitated carbide morphology is investigated. A preliminary pre-tempering treatment at 200°C, 350°C, and 500°C for 2 hours was followed by a 3-hour final tempering step at 650°C. The findings revealed unique temperature-dependent decomposition characteristics of M/A islands. For example, at 200°C, partial M/A island decomposition took place, resulting in long rod-shaped carbides during final tempering. Meanwhile, the 350°C pre-tempering specimen revealed aggregated carbide precipitates of varying sizes in former M/A island locations. In contrast, the 500°C pre-tempering specimen showed coarse globular carbides and the absence of carbide precipitate clustering. This result can be attributed to the decrease in surface energy associated with the carbide-matrix interface as size increases. After tempering, all specimens produced three types of precipitates: rod-shaped Fe3C carbides, rhombus-shaped Mn7C3, and globular-shaped Mn23C6 carbides. The formation of long rod-shaped carbides during M/A island decomposition reduces the critical cleavage stress for micro-crack initiation, jeopardizing steel mechanical properties. Aggregated carbides cause the simultaneous formation of numerous micro-voids in close proximity, which eventually merge to form a large crack, resulting in material failure. When compared to other pre-tempered and directly tempered specimens, pre-tempering at 500°C produced the most favorable microstructure in terms of impact properties.

Logic-in-memory application of ferroelectric-based WS2-channel field-effect transistors for improved area and energy efficiency

In this study, we applied ferroelectrics to the gate stack of Field Effect Transistors (FETs) with a 2D transition-metal dichalcogenide (TMDC) channel, actively researching for sub-2nm technology node implementation. Subsequently, we analyzed the circuit characteristics of Logic-in-Memory (LiM) operation and utilized LiM features after applying ferroelectrics to achieve a single-device configuration. Based on well-calibrated simulations, we performed compact modeling in a circuit simulator to depict the temperature-dependent electrical characteristics of ferroelectric FETs with a double gate structure and 2D channel (DG 2D-FeFET) in sub-2nm dimensions. Through this, we have confirmed that the 2D FeFET-based LiM technology, designed for the 2 nm technology node, exhibits superior characteristics in terms of delay, power/energy consumption, and circuit area under all temperature conditions, compared to the conventional CMOS technology based on 2D FETs. This verification serves as proof of the future technological potential of 2D-FeFET in extremely scaled-down technology nodes.

Temperature-Dependent electrical and dielectric characteristics of lead germanate Pb5Ge1.5Sn1.5O11

A solid-state reaction was used to synthesize the tin modified lead germanate: Pb5Ge1.5Sn1.5O11 (PGSO). The composition was modified to enhance its dielectric and electrical properties. The PGSO sample was characterized by various analytical techniques, such as XRD for structural analysis and FTIR for additional structural information. The surface morphology and features of PGSO were examined by SEM, while its band gap was determined by UV–Visible-Diffuse Reflectance Spectroscopy absorbance spectra. The impedance, dielectric behaviour, AC conductivity, activation energy, and modulus of PGSO were also studied. The temperature dependence of the dielectric constant and AC conductivity showed an increase with increasing temperature. The electrical resistivity (R) decreased as the temperature increased from 100 °C to 300 °C, exhibiting a NTCR behaviour for PGSO sample, which could be applied as a high temperature thermistor and sensor, and could be used to fabricate a high sensitivity, low-cost thermistor. The circuit parameters such as bulk resistance (Rb), frequency factor (n), and bulk capacitance (Cb) were determined by fitting the Nyquist plot using an equivalent circuit (CQR)(CR).

Analyzing Various Structural and Temperature Characteristics of Floating Gate Field Effect Transistors Applicable to Fine-Grain Logic-in-Memory Devices.

Although the von Neumann architecture-based computing system has been used for a long time, its limitations in data processing, energy consumption, etc. have led to research on various devices and circuit systems suitable for logic-in-memory (LiM) computing applications. In this paper, we analyze the temperature-dependent device and circuit characteristics of the floating gate field effect transistor (FGFET) source drain barrier (SDB) and FGFET central shallow barrier (CSB) identified in previous papers, and their applicability to LiM applications is specifically confirmed. These FGFETs have the advantage of being much more compatible with existing silicon-based complementary metal oxide semiconductor (CMOS) processes compared to devices using new materials such as ferroelectrics for LiM computing. Utilizing the 32 nm technology node, the leading-edge node where the planar metal oxide semiconductor field effect transistor structure is applied, FGFET devices were analyzed in TCAD, and an environment for analyzing circuits in HSPICE was established. To seamlessly connect FGFET-based devices and circuit analyses, compact models of FGFET-SDB and -CSBs were developed and applied to the design of ternary content-addressable memory (TCAM) and full adder (FA) circuits for LiM. In addition, depression and potential for application of FGFET devices to neural networks were analyzed. The temperature-dependent characteristics of the TCAM and FA circuits with FGFETs were analyzed as an indicator of energy and delay time, and the appropriate number of CSBs should be applied.

Anisotropic thermal expansion tensor of β -Ga2O3 and its critical role in casting-grown crystal cracking

Thermal expansion tensor represents a key parameter for the numerical modeling of the crystal growth process. However, the modeling of β-Ga2O3 commonly utilizes one single thermal expansion constant that misses its anisotropic nature and temperature-dependent characteristics. Herein, we addressed this limitation by calibrating an anisotropic, temperature-dependent thermal expansion tensor using the experimental lattice parameters of β-Ga2O3 up to 1200 K. We found that COMSOL Multiphysics simulations employing the calibrated tensor yield stress distribution remarkably distinct from those relying on the commonly assumed constants. Specifically, our simulations predict a von Mises stress concentration near the crystal bottom, which explains the experimentally observed crack formation at corresponding locations. This contrasts with the simulations using the single-value thermal expansion constant, which fails to predict such stress concentration. The physical origin of crystal cracking is found to be rooted in the compressive force exerted by the iridium crucible during the cooling process. Our findings suggest that the physical anisotropy of β-Ga2O3 should be carefully considered in modeling and simulation. With the calibrated thermal expansion tensor, we provide a validated set of thermomechanical parameters for reliable β-Ga2O3 crystal growth simulations.

Thermonanomechanics of graphene oxide-M13 bacteriophage nanocomposites -towards graphene-based nanodevices

The self-assembly of graphene oxide (GO) and M13 bacteriophage results in the formation of micro-porous structures, known as GraPhage13 aerogels (GPA). Given the limited applications of aerogels in industry due to their nanomechanical properties, along with the previously observed temperature-dependent characteristics in graphene-based nanocomposites, a thorough exploration of the thermosensitive nanomechanical properties of GPA is essential. Herein, a comprehensive characterisation of the morphology, composition, and spectroscopic analysis of the GPA for a range of temperatures has been conducted and correlated with its nanomechanical properties. Elevated temperatures have been found to lead to gradual removal of oxygen-containing functional groups (OCFGs) from GPA, resulting in increased structural defects and reduced stiffness. Notably, unique nanomechanical behaviours of GPA have been further identified, where the thermal expansion of sp3 bonds exceeds that of a crystalline sp3 structure, while the thermal contraction of sp2 bonds in GPA is found to be between graphite and GO. This underscores the impact of GO functionalisation on the thermal expansion behaviour of GPA. The obtained insights enhance the overall comprehension of the temperature annealing impact on GPA and highlight the tunability of its nanomechanical properties, showcasing a broad potential of this novel nanocomposite across a diverse range of applications.

Temperature dependence of electrochemical characteristics on the growth surface and isomorphous perpendicular surface of DD6

Electrochemical machining (ECM) is a highly effective method for processing nickel-based single crystal (NBSC) superalloys. However, the influence of temperature on the electrochemical corrosion of NBSC remains underexplored. This study investigates the temperature dependence of the corrosion characteristics on the growth surface and its isomorphous perpendicular surface of NBSC DD6 were investigated. Results indicate that temperature significantly impacts the passivation and dissolution processes of the material: at low temperatures, the passivation effect weakens, and the differences in self-corrosion potential between phases decrease, leading to smaller variations in corrosion. Additionally, a mechanism is proposed to elucidate the temperature-dependent corrosion behaviors on different surfaces.

Modeling of the influence of field electron emission from a cathode with a thin insulating film on its sputtering in a gas discharge in a mixture of argon and mercury vapor

A model of the low-current gas discharge in a mixture of argon and mercury vapor in the presence of a thin insulating film on the cathode surface is proposed. The model takes into account that in such a mixture a substantial contribution to the ionization of the working gas can come from the ionization of mercury atoms during their collisions with metastable excited argon atoms. In the discharge, positive charges accumulate on the film surface, creating an electric field in the film sufficient to cause field emission of electrons from the cathode metal substrate into the insulator. Such electrons are accelerated in the film by the field and can escape from it into the discharge volume. As a result, the effective yield of ion-electron emission from the cathode increases. The temperature dependences of discharge characteristics are calculated and it is shown that, due to a rapid decrease in the concentration of mercury vapor in the mixture with decreasing temperature, the electric field strength in the discharge gap and the discharge voltage increase. The presence of a thin insulating film on the cathode can result in an improvement in its emission characteristics and a significant reduction in the discharge voltage. This causes a decrease in the energies of the ions and atoms bombarding the cathode surface, and, consequently, in the intensity of cathode sputtering in the discharge.

Comparative Plasma Nitrocarburizing of AISI 316L and AISI 304 Steels Using a Solid Carbon Active Screen: Differences in the Developing Microstructures

This paper features a direct comparison of the response of AISI 316L and AISI 304 austenitic stainless steels to active screen plasma nitrocarburizing applied for a wide range of treatment temperatures from 380 °C to 480 °C (653 K to 753 K). Thereby, an active screen made of solid carbon was used without applying bias plasma to the treated steel samples. Since it is believed that the result of treatment strongly depends on the concentration of in-situ generated hydrogen cyanide, the conditions of the treatments were adapted to keep this concentration constant. Under such treatment conditions, it was shown that AISI 316L has a lower tendency to form CrN than AISI 304 at comparable treatment temperatures, where the threshold temperature was found below 480 °C (753 K) for the former and below 440 °C (713 K) for the latter. In addition, the decomposition of expanded austenite generated on the treated AISI 316L at high temperatures leads to CrN and (mainly) Cr-depleted austenite phase, which is possibly accompanied by minor amounts of α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}-ferrite. Instead, for the treated AISI 304, decomposition leads to CrN and transformed α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}-ferrite phase. The modified layer thicknesses achieved after a given treatment duration and the kinetics of the layer growth showed a characteristic temperature dependence for each steel, which is discussed in accordance with the results of microstructure analysis.

Composite embedded track structure considering temperature dependent characteristics for rolling noise reduction of inter-city railway system

Intercity railway will generate strong noise when passing through the surrounding residents, among which rolling noise is the main noise source and is difficult to control. A composite embedded track structure containing polymer material was fabricated to analyze its damping and rolling noise reduction characteristics. The damping characteristics of polymer materials of embedded track were tested by dynamic thermo-mechanical analyzer (DMA Q800). The frequency response function (FRF) of the embedded track system is tested by force hammer percussion method. The vibration of the embedded track is simulated by the the 2.5-dimensional finite element method (2.5D FEM) considering damping characteristics obtained by material test of DMA Q800. The sound radiation model of embedded track is developed by using 2.5-dimensional sound boundary element method (2.5D BEM). The model is verified by the test. The FRF, track decay rate, and wheel-rail force at different temperatures are analyzed. With the decrease of temperature, the elastic modulus and loss factor of polymer material of embedded track increase, which will affect the above results. Sound directivity and effect on wheel-rail noise reduction of embedded track have been studied. The results show that the composite embedded track has good damping characteristics and noise reduction performance. Sound sensitivity analysis of loss factors of the three polymer materials of embedded track is carried out to improve embedded track noise reduction capability.

Impact of dopant concentration on the structural, morphological, and spectroscopic characteristics of Eu3+-doped Sr10(PO4)6F2 nanomaterials, including temperature-dependent emission

Luminescent materials with desirable properties are in constant demand for lighting applications and as probes in bioimaging. In this study, we successfully synthesized nanosized strontium fluorapatite (SrFAp) powders doped with varying concentrations of Eu3+ ions via the hydrothermal method, targeting applications in lighting and bioimaging probes. Our focus was on understanding the impact of annealing temperature and dopant concentration on structural purity, particle morphology, photoluminescence, dopant ion occupancy, and temperature-dependent emission characteristics. The materials emit red light, with the most intense transition being 5D0→7F2. The asymmetry parameter (R) determination and CIE color coordinates provided insights into the spectroscopic attributes. Emission spectra were measured and discussed at four distinct excitation lines. Lower-energy excitation wavelengths, deemed favorable for organisms, make these materials particularly suitable for bioimaging applications. While the most intense emission occurred under 393 nm excitation, emissions were also detected at 464.5 nm and 525 nm, suggesting alternative excitation wavelengths better suited for bioimaging. Additionally, we conducted extensive studies to assess the effect of ambient temperature on the emission intensity of SrFAp materials doped with 1 mol% Eu3+ ions. Thermal quenching of luminescence was observed in both as prepared and annealed materials, providing insights into the temperature-dependent behaviour of the emission properties.

Temperature-dependent tuning of band gap of Fe3O4 nanoparticles for optoelectronic applications

We have investigated structural, morphological and temperature dependent absorption characteristics of Fe3O4 nanoparticles. X-ray diffraction pattern exhibited six diffraction peaks belonging to the cubic phase structure with lattice parameter of a = 8.1602 Å. Spectral variation of absorption coefficient were utilized to achieve Tauc and spectral derivative analyses providing the band gap of the Fe3O4 at varying temperature. The band gap of Fe3O4 nanoparticles was found around 2.08 eV at 300 K and around 2.14 eV at 10 K. The band gap variation with applied temperatures between 10 and 300 K were also investigated using Varshni relation.

Control-gate-free reconfigurable transistor based on 2D MoTe2 with asymmetric gating

As transistor footprint scales down to the sub-10 nm regime, the process development for advancing to further technology nodes has encountered slowdowns. Achieving greater functionality within a single chip requires concurrent development at the device, circuit, and system levels. Reconfigurable transistors possess the capability to transform into both n-type and p-type transistors dynamically during operation. This transistor-level reconfigurability enables field-programmable logic circuits with fewer components compared to conventional circuits. However, the reconfigurability requires additional polarity control gates in the transistor and potentially impairs the gain from a smaller footprint. In this paper, we demonstrate a 2D control-gate-free reconfigurable transistor based on direct modulation of out-of-plane conduction in an ambipolar MoTe2 channel. Asymmetric electrostatic gating at the source and drain contacts is employed in the MoTe2 transistor resulting in different Schottky barrier widths at the two contacts. Consequently, the ambipolar conduction is reduced to unipolar conduction, where the current flow direction determines the preferred carrier type and the transistor polarity. Temperature dependence of the transfer characteristics reveals the Schottky barrier-controlled conduction and confirms that the Schottky barrier widths at the top contact are effectively tuned by electrostatic gating. Without the complexity overhead from polarity control gates, control-gate-free reconfigurable transistors promise higher logic density and lower cost in future integrated circuits.

Li4 Zn(PO4 )2 :Mn2+ thermosensitive phosphor with dual luminescent centres for optical thermometry.

An optical thermometry strategy based on Mn2+ -doped dual-wavelength emission phosphor has been reported. Samples with different doping content were synthesized through a high-temperature solid-phase method under an air atmosphere. The electronic structure of Li4 Zn(PO4 )2 was calculated using density functional theory, revealing it to be a direct band gap material with an energy gap of 4.708 eV. Moreover, the emitting bands of Mn2+ at 530 and 640 nm can be simultaneously observed when using 417 nm as the exciting wavelength. This is due to the occupation of Mn2+ at the Zn2+ site and the interstitial site. Further analysis was conducted on the temperature-dependent emission characteristics of the sample in the range 293-483 K. Mn2+ has different responses to temperature at different doping sites in Li4 Zn(PO4 )2 . Based on the calculations using the fluorescence intensity ratio technique, the maximum relative sensitivity at a temperature of 483 K was determined to be 1.69% K-1 , while the absolute sensitivity was found to be 0.12% K-1 . The results showed that the Li4 Zn(PO4 )2 :Mn2+ phosphor has potential application in optical thermometry.