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Ultralow loss and temperature stability of Li3Mg2NbO6-xLiF ceramics with low sintering temperature
摘要： Novel temperature stable Li3Mg2NbO6-xLiF (x=0.5-8 wt. %) ceramics with ultralow loss were fabricated by the solid-state reaction process. The influence of LiF addition on the sintering, grain growth and morphology, and improved microwave dielectric characteristics was investigated. A single orthorhombic Li3Mg2NbO6 structure could be confirmed by Raman spectra and XRD patterns. Dense and homogeneous microstructure could be obtained with ~10 μm average grain size. Results demonstrated that the εr values were relevant to bulk density and the high Q×f values were influenced by the large grain sizes. The τf values depend on porosity corrected dielectric constant. Notably, the remarkably desirable microwave dielectric characteristics: εr=15.4, Q×f=100,000 GHz, τf=?3.1 ppm/°C were achieved for the Li3Mg2NbO6 ceramics with x=6 wt% sintered at 925 °C, which could be applied for ultra-low loss LTCC applications.
关键词： ultra-low loss,temperature stability,single orthorhombic structure
更新于2025-09-04 15:30:14
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Raman thermometry in water, ethanol and ethanol/nitrogen-mixtures from ambient to critical conditions
摘要： We present investigations into remote liquid temperature sensing with Raman spectroscopy using different evaluation methods for the OH stretching vibration band. Water, ethanol and ethanol saturated with nitrogen, all as liquids or liquid-like supercritical fluids, are pumped through a heated microcapillary system at elevated pressures. Raman spectra are recorded from the liquid inside the microcapillary and are evaluated with respect to the temperature sensitivity of the OH stretching vibration. The four approaches applied are (i) to evaluate the center position of the Raman OH-band, (ii) the integrated absolute difference spectrum, (iii) the intensity ratio of two regions of the OH-band, and (iv) the intensity ratio of two fitted Gaussian peaks. The temperature range investigated covers from ambient temperature to the component’s respective boiling temperature or critical temperature at sub- and supercritical pressures. Precision and robustness of the employed methods are characterized. It is shown that two out of the four methods feature temperature deviations smaller than 5 K at all pressures, and that one method can also be applied to liquid mixtures of ethanol and nitrogen. Applicability to other liquids and mixtures is discussed.
关键词： temperature sensing,supercritical fluids,OH stretching vibration,water,Raman spectroscopy,nitrogen,microcapillary,ethanol
更新于2025-09-04 15:30:14
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Abnormal Curie-temperature shift in Ho-doped BaTiO3 ceramics with the self-compensation mode
摘要： Nominal (Ba1?xHox)(Ti1?xHox)O3 ceramics (BHTH) were prepared at 1400 °C using a mixed-oxides method. The structure, microstructure, dielectric properties, and point defects of BHTH were investigated using X-ray di?raction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, electron paramagnetic resonance (EPR), and dielectric measurements. Ho3+ in BaTiO3 prefers a self-compensation mode with a slight Ba-site preference, and the solubility limit of Ho3+ in the ?ne-grained BHTH (0.5 μm) was determined by XRD to be x = 0.03. An abnormal phenomenon was observed: the Curie temperature of BHTH shifted towards high temperatures from 128 °C at x = 0.01 to 131 °C at x = 0.03. Ho3+ is inferred to be a potential codopant to achieve X8R speci?cation when BaTiO3 is doped with Ho3+ and other types of ions.
关键词： Self-compensation mode,Point defects,Ho-doped BaTiO3,The Curie temperature,Dielectrics
更新于2025-09-04 15:30:14
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Er3+-to-Yb3+ and Pr3+-to-Yb3+ energy transfer for highly efficient near-infrared cryogenic optical temperature sensing
摘要： Here, the very high thermal sensing capability of Er3+,Yb3+ doped LaF3 nanoparticles, where Er3+-to-Yb3+ energy transfer is used, are reported. Also Pr3+,Yb3+ doped LaF3 nanoparticles, with Pr3+-to-Yb3+ energy transfer, showed temperature sensing in the same temperature regime, but with lower performance. The investigated Er3+,Yb3+ doped LaF3 nanoparticles show a remarkably high relative sensitivity Sr up to 6.6092 %K-1 (at 15K) in the near-infrared (NIR), in the cryogenic (15 – 105K) temperature region opening a whole new thermometric system suitable for advanced applications in the very low temperature ranges. Up to date reports on NIR cryogenic sensors are very scarce.
关键词： near-infrared,Pr3+-to-Yb3+ energy transfer,Er3+-to-Yb3+ energy transfer,LaF3 nanoparticles,cryogenic temperature sensing
更新于2025-09-04 15:30:14
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Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy
摘要： A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+d and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions.
关键词： electron-phonon interaction,high-temperature superconductors,cuprate,time-resolved ARPES,nodal-antinodal dichotomy,angle-resolved photoemission spectroscopy,quasiparticles
更新于2025-09-04 15:30:14
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Quartz-enhanced conductance spectroscopy for nanomechanical analysis of polymer wire
摘要： Quartz-enhanced conductance spectroscopy is developed as an analytical tool to investigate dynamic nanomechanical behaviors of polymer wires, in order to determine the glass transition temperature (Tg). A polymethyl methacrylate (PMMA) microwire with a diameter of 10 lm was bridged across the prongs of a quartz tuning fork (QTF). With the advantage of QTF self-sensing as compared with micro-cantilevers or other resonators, the resonance frequency and Q factor can be directly determined by means of its electrical conductance spectra with respect to the frequency of the external excitation source (dI/dV vs f), and therefore, no optical beam is required. The Tg of the PMMA microwire was determined by the maximum loss modulus of the QTF, calculated from the resonance frequency and the Q factor as a function of temperature. The measured Tg of the PMMA is 103 (cid:2)C with an error of 62 (cid:2)C. Both heating/cooling and physical aging experiments were carried out, demonstrating that the technique is both reversible and reproducible.
关键词： PMMA,polymer wire,quartz tuning fork,nanomechanical analysis,glass transition temperature,Quartz-enhanced conductance spectroscopy
更新于2025-09-04 15:30:14
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Glass transition temperature of PMMA/modified alumina nanocomposite: molecular dynamic study
摘要： In this study, the effect of alumina and modi?ed alumina nanoparticles in a PMMA/alumina nanocomposite was investigated. To attain this goal, the glass transition behavior of poly methyl methacrylate (PMMA), PMMA/alumina and PMMA/functionalized alumina nanocomposites were investigated by molecular dynamic simulations (MD). All the MD simulations were performed using the Materials Studio 6.0 software package of Accelrys. To obtain the glass transition temperature, the variation of density versus temperature was obtained. The temperature at which the slope of the density-temperature curve observably changes is de?ned as the glass transition temperature (Tg). The effect of alumina nanoparticles on the Tg was related to the free volume and the mobility of chain segments and the interaction between the alumina nanoparticles and the polymer. The mobility of the chain segments was investigated based on the mean square displacement and radius gyration. The results show that the incensement the Tg of the PMMA/functionalized alumina nanocomposite is more than that of the PMMA/alumina nanocomposite due to the modi?cation of the alumina nanoparticles.
关键词： molecular dynamic,nanocomposite,glass transition temperature,gyration radius
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Thermal Characterization and Design for a High Density GaN-Based Power Stage
摘要： This paper proposes a methodology for extracting the thermal equivalent circuit of a high density GaN-based power stage, using a 48 V to 12 V GaN-based synchronous buck converter as the test platform. The test setup calculates the junction temperatures by measuring Rds,on for both FETs in the half bridge, while current sources produce power losses in each device and the output filter inductor. Independent control of the two gate voltages allows for either symmetric or asymmetric distribution of power loss between the two FETs, and comparison of these results are used to calculate the coupled and uncoupled thermal resistances between them. The thermal interaction with the filter inductor is similarly modeled. The baseline thermal design with a bare PCB and no heatsink was characterized, as well as a proposed thermal solution consisting of a heatsink, gap pad, gap filler, and a plastic shim. Each configuration was tested with three air flow conditions, and the resulting thermal model was used to estimate the maximum current capability without exceeding 100 °C on either FET. The proposed thermal solution improves the maximum current-handling capability by over 60% compared with the baseline design.
关键词： thermal characterization,eGaN FET,thermal design,HEMT,HFET,heatsink,junction temperature,GaN
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Surge current capability of SiC MOSFETs in AC distribution systems
摘要： Whereas short circuit current and time ratings for power converter applications are often stated by SiC device manufacturers, surge current capability for AC electrical apparatus applications are rarely available. This paper present the experimental validation of surge current capability of selected SiC devices for low voltage AC distribution system applications. Because AC electrical apparatus, such as relays, contactors, and circuit breakers, have a different set of system parameters and requirements compared to traditional power converter applications, power semiconductor devices need to be validated from a different point of view. In fact, robustness to inductive short circuit currents, inrush currents, short and long time overload are some of the basic requirements for the utilization of WBG devices for these applications. In this paper, we compare the performance of different SiC MOSFETs under different types of AC waveform conditions.
关键词： semiconductor device characterization,temperature measurement,solid state circuit breaker,WBG semiconductor devices,overload capability,surge current,SiC MOSFET,electrical apparatus
更新于2025-09-04 15:30:14
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A low temperature approach for photo/cathodoluminescent Gd <sub/>2</sub> O <sub/>2</sub> S:Tb (GOS:Tb) nanophosphors
摘要： Titrating the aqueous solution of equimolar RE(NO3)3 and (NH4)2SO4 with NH4OH to pH~9 at ~4 °C produced an amorphous precursor that yielded phase-pure and well dispersed RE2O2S nanopowder (RE=Gd0.99Tb0.01; GOS:Tb) via a RE2O2SO4 intermediate upon annealing in H2. The powders calcined at the typical temperatures of 700/1200 °C exhibited unimodal size distributions and have the average crystallize sizes of ~17/55 nm, average particle sizes of ~284/420 nm, and specific surface areas of ~14.62/4.53 m2/g (equivalent particle sizes: ~56/180 nm). The 1200 °C product exhibited sharp green luminescence at ~544 nm (FWHM = 2.3 nm; λex = 275 nm), with an absolute quantum yield of ~24.8% and a fluorescence lifetime of ~1.34 ms at room temperature. It was also shown that the powder possesses favorable thermal stability (the activation energy for thermal quenching of luminescence ~0.305 eV) and is stable under electron beam irradiation up to 7 kV and 50 μA. The synthetic technique has the advantages of scalability and favorable dispersion and high chemical/phase purity for GOS powder, which may allow the sintering of scintillation ceramics at lower temperatures.
关键词： low-temperature processing,oxysulfide,GOS,luminescence,nanopowder
更新于2025-09-04 15:30:14