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Nonvacuum Surfacing of Protective Coatings Using a Low-Energy Electron Beam
摘要： The results of electron-beam surfacing in air of protective coatings by a low-energy (120 keV) electron beam produced by an electron gun with a plasma emitter are presented. The gun is mounted on an industrial robotic manipulator KUKA, which allows the electron beam to be moved to the atmosphere along a given path without electromagnetic sweep. The combined (self-propagating high-temperature synthesis and electron-beam surfacing) method for obtaining coatings from reaction mixtures of TiO2 : 2.1C and TiO2 : 0.3Cr2O3 : 3.3С is implemented using this setup. The optimum composition of the reaction mixtures and the deposition regimes are determined by thermodynamic modeling using the TERRA program. The obtained coatings with a thickness of 120–200 μ m have a microhardness of 12 GPa. The coatings and the transition layer are established to have good heat resistance up to 900°C. Noticeable changes in the weight characteristics of coatings occur at above 1000°C.
关键词： electron beam surfacing at atmospheric pressure,microhardness,plasma emitter,electron beam,differential pumping system,carbide coatings,self-propagating high-temperature synthesis (SHS),electron gun,gas discharge
更新于2025-09-10 09:29:36
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High temperature dielectrics based on Bi1/2Na1/2TiO3-BaTiO3-Sr0.53Ba0.47Nb2O6 ceramics with high dielectric permittivity and wide operational temperature range
摘要： Lead-free (1-x) (0.94Bi1/2Na1/2TiO3 ?0.06BaTiO3)-xSr0.53Ba0.47Nb2O6 (BNBT-xSBN, x = 0–0.04) ceramics are fabricated through a conventional solid-state reaction method. The structure and dielectric properties are systematically investigated. The dielectric permittivity of BNBT-xSBN is suppressed by the doping of SBN. The temperature of the dielectric peak in the lower temperature range decreases with increasing SBN content. As the SBN doping content increases from 0.01 to 0.04, the temperature range with the stable dielectric permittivity (ε ± 15%, 1 kHz), taking the ε value at 150 °C as the base point, expands from 319 °C to 383 °C. In addition, at a composition of x = 0.01, the sample shows higher dielectric permittivity (3964 ± 15%, 1 kHz) in a wide temperature range (89–408 °C). These results indicate that the Bi1/2Na1/2TiO3-BaTiO3-xSr0.53Ba0.47Nb2O6 ceramic is a promising candidate for thermally stable electronic capacitors in high temperature environments.
关键词： High temperature capacitor,Lead-free,Dielectric stable
更新于2025-09-10 09:29:36
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Systematic Investigation of Spontaneous Emission Quantum Efficiency Drop up to 800K for Future Power Electronics Applications
摘要： Future high-density power electronics applications may require optoelectronic devices for gate drive. Thus, a systematic study of optoelectronic material from 10 K to 800 K has been performed to understand the potential of the high-temperature operation of optoelectronic devices. The temperature dependence of the photoluminescence (PL) of InGaN/GaN multiple quantum wells (MWQs) was studied. The integrated PL intensity dropped by an order of magnitude at 800 K as compared to 10 K. The spontaneous emission quantum efficiency was calculated from the power-law relation linking the integrated PL signal and the excitation pump power. The validation of the traditional ABC model for solid-state lighting is extended to 800 K. This work demonstrates the feasibility of developing high-temperature optoelectronic devices, which have operating temperatures over 500 K.
关键词： high temperature photoluminescence,high temperature efficiency,power dependent photoluminescence,InGaN/GaN MWQs,power module,quantum temperature optoelectronics
更新于2025-09-09 09:28:46
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High Temperature Operation Limit Assessment for 4H-SiC Schottky Diode-based Extreme Temperature Sensors
摘要： We developed a simplified theoretical model for parameters calculation of diode temperature sensors (DTS) based on Schottky diodes (SD). The current flow mechanism of the diodes considered was dominated by over-barrier thermionic emission. Qualitative correlations between basic fundamental and electrophysical parameters of such DTS were established. The expressions for ultimate high-temperature parameters of the DTS were obtained. Theoretical results obtained were approved using test samples of DTS with Schottky contact Ni/n-SiC (4H). It was shown that physical high-temperature limit of operation of such a DTS (>1250 K) exceeded the values of commercial DTS based on Si, GaAs, AlGaAs p-n junctions. And the SD-based DTS itself demonstrated significantly lower energy consumption.
关键词： wide bandgap,thermal sensitivity,high temperature,Schottky diode,temperature sensor,semiconductor,thermal limit
更新于2025-09-09 09:28:46
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Elastic and thermophysical properties of BAs under high pressure and temperature
摘要： The pseudopotential plane-wave approach in the framework of the density functional theory, and the density functional perturbation theory with the generalized gradient approach for the exchange-correlation functional has been used to calculate the structural phase stability, elastic constants and thermodynamic properties of boron-arsenide (BAs) compound. The BAs compound transforms from the zincblende phase to rock-salt structure; the phase transition pressure was found to be 141.2 GPa with a volume contraction of around 8.2 %. The thermodynamic properties under high pressure and temperature up to 125 GPa and 1200 K respectively were also determined, analyzed and discussed in comparison with other data of the literature. The systematic errors in the static energy were corrected using the bpscal EEC method. Our results agree well with those reported in the literature, where for example, our calculated melting temperature (2116 K) deviates from the theoretical one (2132.83 K) with only 0.8 %, and the deviation between our result (1.86) of the Grüneisen parameter and the theoretical one (1.921) is only around 3.2 %.
关键词： Phase transition,Thermodynamic properties,High-pressure,High-temperature,Boron arsenide
更新于2025-09-09 09:28:46
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by means of high-pressure–high-temperature Raman experiments
摘要： We report here high-pressure–high-temperature Raman experiments performed on BiVO4. We characterized the fergusonite and scheelite phases (powder and single crystal samples) and the zircon polymorph (nanopowder). The experimental results are supported by ab initio calculations, which, in addition, provide the vibrational patterns. The temperature and pressure behavior of the fergusonite lattice modes reflects the distortions associated with the ferroelastic instability. The linear coefficients of the zircon phase are in sharp contrast to the behavior observed in the fergusonite phase. The boundary of the fergusonite-to-scheelite second-order phase transition is given by TF ?Sch(K) = ?166(8)P (GPa) + 528(5). The zircon-to-scheelite, irreversible, first-order phase transition takes place at TZ?Sch(K) = ?107(8)P (GPa) + 690(10). We found evidence of additional structural changes around 15.7 GPa, which in the downstroke were found to be not reversible. We analyzed the anharmonic contribution to the wave-number shift in fergusonite using an order parameter. The introduction of a critical temperature depending both on temperature and pressure allows for a description of the results of all the experiments in a unified way.
关键词： zircon,scheelite,BiVO4,fergusonite,high-temperature,phase transition,high-pressure,ab initio calculations,Raman experiments,vibrational patterns
更新于2025-09-09 09:28:46
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High temperature impedance properties and conduction mechanism of W <sup>6+</sup> -doped CaBi <sub/>4</sub> Ti <sub/>4</sub> O <sub/>15</sub> Aurivillius piezoceramics
摘要： Effects of W6+ doping on the phase structural and electrical properties, especially the conduction mechanism at a higher temperature of CaBi4Ti4O15 Aurivillius piezoceramics, have been investigated systematically. The conductivity properties at a temperature range from 500 °C to 650 °C have been characterized by complex impedance spectroscopy. The conductivity shows a nature of ionic conduction mechanism and non-Debye relaxation process at a higher temperature. The non-Debye relaxation behavior and conduction process are dominated by the jump of charge carriers, which can be demonstrated by the similar values of the relaxation activation energy (1.45 eV), hopping conduction energy (1.50 eV), and dc conduction energy (1.39 eV). Meanwhile, the piezoelectric coef?cient d33 of CaBi4Ti4O15 has been improved from 7.5 pC/N to 17.8 pC/N and keeps good temperature stability up to 650 °C with appropriate W6+ doping. These results provide a profound insight into the conduction process and mechanism from the viewpoint of microstructure, which is greatly bene?cial for the high-temperature application of Aurivillius piezoceramics.
关键词： Aurivillius piezoceramics,impedance properties,conduction mechanism,CaBi4Ti4O15,high temperature,W6+-doped
更新于2025-09-09 09:28:46
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High-Temperature Large-Scale Self-Assembly of Highly Faceted Monocrystalline Au Metasurfaces
摘要： Localized surface plasmon resonance (LSPR) devices based on resonant metallic metasurfaces have shown disruptive potential for many applications including biosensing and photocatalysis. Despite significant progress, highly performing Au plasmonic nanotextures often suffer of suboptimal electric field enhancement, due to damping effects in multicrystalline domains. Fabricating well-defined Au nanocrystals over large surfaces is very challenging, and usually requires time-intensive multi-step processes. Here, presented are first insights on the large-scale self-assembly of monocrystalline Au nano-islands with tunable size and separation, and their application as efficient LSPR surfaces. Highly homogeneous centimeter-sized Au metasurfaces are fabricated by one-step deposition and in situ coalescence of hot nanoparticle aerosols into a discontinuous monolayer of highly faceted monocrystals. First insights on the mechanisms driving the high-temperature synthesis of these highly faceted Au nanotextures are obtained by molecular dynamic and detailed experimental investigation of their growth kinetics. Notably, these metasurfaces demonstrate high-quality and tunable LSPR, enabling the fabrication of highly performing optical gas molecule sensors detecting down to 3 × 10?6 variations in refractive index at room temperature. It is believed that these findings provide a rapid, low-cost nanofabrication tool for the engineering of highly homogenous Au metasurfaces for large-scale LSPR devices with application ranging from ultrasensitive optical gas sensors to photocatalytic macroreactors.
关键词： scalable,gold,grain boundaries,crystals,high temperature,sensing,plasmonics
更新于2025-09-09 09:28:46
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Properties of percolation channels in planar memristive structures based on epitaxial films of a YBa <sub/>2</sub> Cu <sub/>3</sub> O <sub/> 7? <i>δ</i> </sub> high temperature superconductor
摘要： The transport properties of the percolation channels of memristive structures based on YBa2Cu3O7?δ epitaxial ?lms were studied. Molecular electronics and Andreev re?ection spectroscopy were utilised, and the in?uence of the superconductive transition of electrodes on resistive switching effects in these structures was examined. Based on the analysis of the conductivity mechanisms in the obtained heterostructures, it is assumed that percolation channels form through a chain of domains disordered by oxygen about 10 nm in diameter, with a maximum Tc of 60 K. Zero-bias anomalies of the dynamic resistance of the studied structures display temperature dependence of the critical current of typical superconductor—normal—superconductor weak links within the framework of Kulik–Omel’yanchuk theory in the dirty limit. A simulation was used to determine the physical parameters of the studied heterostructures.
关键词： resistive switching memory,heterostructures,?lms,critical current,high temperature superconductors,oxygen vacancies
更新于2025-09-09 09:28:46
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A Wideband HTS Filter Using Strong Coupling Coplanar Spiral Resonator Structure
摘要： A novel coplanar spiral resonator structure (CSRS), which has a stronger coupling strength than normal CPW structure, is introduced. This structure helps to realize the remarkable strong coupling required for low-frequency wideband ?lters. Although no grounded stubs are deployed to balance the ground plane, the slot-line mode of the ?lter is not excited. An eight-pole wideband high-temperature superconducting (HTS) ?lter, with a fractional bandwidth (FBW) of 50% and a center frequency of 322MHz, is developed. The ?lter is designed and fabricated on a 0.5-mm-thick LaAlO3 substrate with a core size of 41mm × 22mm. The measured minimum insertion loss is 0.05dB and the ?rst spurious peak appears at 842 MHz, which is about 2.6 times the center frequency. The measured results agree well with the simulated results.
关键词： high-temperature superconducting (HTS),Wideband bandpass ?lter,coplanar waveguide (CPW)
更新于2025-09-09 09:28:46