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Influence of Se on Properties of As-S-Se-I Glass for Immersion Mid-IR Leds Lenses
摘要： The study of glass components influence on the physical and chemical properties of As–S–Se–I glasses has the potential to help design glasses with the required properties. A change of certain glass properties upon the introduction of selenium into AsSI glass was demonstrated. Non-stoichiometric compounds along the As2S3-AsI3-Se diagram section were investigated by differential thermal analysis, ultrasonic measurements, dilatometric measurements. It has been shown that the introduction of selenium decreases the glass solubility in water. Change in the glass properties with the change in the short-range structure studied by Raman spectroscopy was shown. These glasses can be used for creation of immersion lenses and optical adhesives which change radiation characteristics of mid-IR LEDs.
关键词： coefficient of thermal expansion,mechanical characteristics,density,solubility,chalcogenide glass,Raman spectra
更新于2025-09-16 10:30:52
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Thermal expansion behavior of CNT reinforced AlSi10Mg composite fabricated via laser powder bed fusion
摘要： Carbon nanotube (CNT) reinforced Al matrix composite exhibit good dimensional stability and can be a promising material with low coef?cient of thermal expansion (CTE). The thermal expansion behavior of CNT/AlSi10Mg composite with the CNTs content from 0 wt% to 2 wt% fabricated via laser powder bed fusion (LPBF) was investigated in this research. The CTE of all samples increased generally as the temperature increasing. At the same temperature, the CTE of the samples was smaller when CNTs content is lower. The best dimensional stability was reached as CNTs content was 2 wt%. The CTE deceased to 29.08 × 10?6 °C?1, as much as 16% reduction compared with unreinforced AlSi10Mg at 300 °C. The solid solution and precipitation behavior of Si in matrix and the interruptions of Si network resulted in the ?uctuation during dimension increase. With the CNTs distributed along the cell boundary, the Si network was consolidated. Hence, the microstructure of the composite became more stable and the CTE got lower with the addition of CNTs increasing. Moreover, the experimental results were similar to the predicted value of the thermoelastic model.
关键词： laser powder bed fusion,CNTs,coef?cient of thermal expansion,network
更新于2025-09-16 10:30:52
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Stress-controlled decomposition routes in cubic AlCrN films assessed by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction
摘要： The dependence of decomposition routes on intrinsic microstructure and stress in nanocrystalline transition metal nitrides is not yet fully understood. In this contribution, three Al0.7Cr0.3N thin films with residual stress magnitudes of ?3510, ?4660 and ?5930 MPa in the as-deposited state were in-situ characterized in the range of 25–1100 °C using in-situ synchrotron high-temperature high-energy grazing-incidence-transmission X-ray diffraction and temperature evolutions of phases, coefficients of thermal expansion, structural defects, texture as well as residual, thermal and intrinsic stresses were evaluated. The multi-parameter experimental data indicate a complex intrinsic stress and phase changes governed by a microstructure recovery and phase transformations taking place above the deposition temperature. Though the decomposition temperatures of metastable cubic Al0.7Cr0.3N phase in the range of 698–914 °C are inversely proportional to the magnitudes of deposition temperatures, the decomposition process itself starts at the same stress level of ~?4300 MPa in all three films. This phenomenon indicates that the particular compressive stress level functions as an energy threshold at which the diffusion driven formation of hexagonal Al(Cr)N phase is initiated, provided sufficient temperature is applied. In summary, the unique synchrotron experimental setup indicated that residual stresses play a decisive role in the decomposition routes of nanocrystalline transition metal nitrides.
关键词： thin films,AlCrN,phase decomposition,thermal expansion,microstructure,in-situ XRD,residual stress
更新于2025-09-12 10:27:22
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Anharmonicity of Bi <sub/>2</sub> Se <sub/>3</sub> revealed by fs transient optical spectroscopy
摘要： We investigate the anharmonic effects in Bi2Se3 crystals using femtosecond transient optical spectroscopy at 5–280 K. The re?ectivity time series consist of exponential decay due to hot carriers and decaying oscillations due to the A1 1g phonon vibration. Vibration frequency and dephasing time of this optical phonon mode are obtained as a function of temperature, decreasing with increasing temperature; both the red shift in frequency and the increased dephasing rate induced by heating can be well described using the anharmonicity model including lattice thermal expansion and phonon-phonon coupling.
关键词： Bi2Se3,femtosecond transient optical spectroscopy,phonon dynamics,anharmonicity,thermal expansion,phonon-phonon coupling
更新于2025-09-11 14:15:04
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Investigation of Temperature Sensitivity of a Polymer-Overlaid Microfiber Mach-Zehnder Interferometer
摘要： The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical microfiber with a strong evanescent field into the MZI, a low index polymer with high thermal characteristics is deposited on the surface of the microfibers to realize a polymer-overlaid microfiber MZI. It was found that the thermal expansion factor in the proposed MZI plays an important role in the temperature sensitivity of the FSR. The temperature sensitivity of the polymer-overlaid microfiber MZI is improved, which is measured to be ?8.29 nm/?C at 25 ?C. The optical transmission spectrum of the polymer-overlaid microfiber MZI is converted to the spatial frequency spectrum via fast Fourier transform. The temperature sensitivity of the spatial frequency in the proposed polymer-overlaid MZI is estimated to be 18.31 pm?1 ?C?1, which is 17 times higher than that of the microfiber MZI without polymer coating (1.04 pm?1 ?C?1).
关键词： temperature sensors,thermo-optic effect,thermal expansion effect,microfibers,microfiber Mach-Zehnder interferometers
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Helium-Based Refractometry for Pressure Measurements in the Range 1–100 kPa
摘要： This paper describes an alternative of pressure measurements based on a helium absolute refractometer at 532 nm. The Fabry-Perot cavity has been characterized from relevant parameters and the resolution in pressure of this new optical pressure sensor is lower than 0.2 Pa.
关键词： Pressure-induced distortion coefficient,Coefficient of thermal expansion,Refractometry,Fabry-Perot cavity,Pressure sensor
更新于2025-09-10 09:29:36
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Real-time observation of the temperature-induced phase transformation in GeTe and its thermal expansion properties
摘要： The GeTe-based system has long been considered as a promising candidate system for various functional applications; many of which are directly related to the polymorphic phase transformation in their crystalline forms. Consequently, the microstructure underlying their intriguing phase transition has been the subject of numerous studies. Here we provide real-time observation of the microstructural changes associated with the reversible pseudo-cubic (or rhombohedral) to cubic GeTe phase transition using high-voltage transmission electron microscopy (HV-TEM) operating at 1,250kV and complementary high-temperature X-ray diffraction (XRD). As a result of the phase transition, the pseudo-cubic GeTe domain’s configuration significantly changes from its original band-like to a spike-like morphology with a different orientation after a heating/cooling cycle. The coefficients of thermal expansion (CTE) properties as a function of temperature are also explored in relation to the GeTe phase transition.
关键词： CTE ellipsoids,in-situ high voltage transmission electron microscopy,GeTe,thermal expansion tensor,ferroelectric domains
更新于2025-09-10 09:29:36
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - A multiphysics approach to an automotive headlamp low beam cut-off line
摘要： In this study, cumulative effect of warpage due to injection molding process and thermal expansion of plastic parts because of heat generated by the light functions on headlamp low beam cut-off line has been inspected by virtual methods. Firstly, deformed mesh generated by mold flow analysis for light module bracket and headlamp housing have been converted to solid computer aided design (CAD) models by the help of commercially available CAD software. Thermal finite element analysis (FEA) has been performed at ambient temperature of 22°C with the light functions all on and stabilized temperature map has been exported for use as load input for structural FEA. After structural FEA, directional displacements and angular rotations of focal point of the light module have been extracted as inputs for optical analysis. Optical analysis results have been inspected to understand the effects on low beam cut-off line of the Headlamp.
关键词： automotive headlamp,low beam cut-off line,multiphysics,thermal expansion,FEA,warpage,optical analysis
更新于2025-09-09 09:28:46
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Difference analysis model for the mismatch effect and substrate-induced lattice deformation in atomically thin materials
摘要： Atomically thin materials hold mutative electronic transition properties by virtue of the inevitable strains adding to the lattice distribution. A quantitative approach and clear systematical verification have seldom been presented to effectively illustrate the substrate-induced strain along the lattice distribution, although the substrate perturbations for monolayers have been repeatedly mentioned. Here, a model of difference analysis is introduced to reveal the structural strain of monolayers from the substrate, which is derived from the mismatch effect based on the variation of the thermal expansion coefficient between the substrate and monolayers. A coupling coefficient is proposed to quantitatively manifest the substrate-induced strain and mismatch effect. Furthermore, combined with the coupling coefficient, the lattice disorder from the mismatch effect is demonstrated, experimentally using the WS2 monolayer as reference. This study could promote broad investigations of some fundamental issues from preparation to electrical structural performances in atomically thin materials and further practical applications.
关键词： atomically thin materials,substrate-induced strain,mismatch effect,WS2 monolayer,thermal expansion coefficient
更新于2025-09-09 09:28:46
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Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites
摘要： Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed.
关键词： structural phase transition,negative thermal expansion,perovskite,scandium trifluoride,antiferrodistortive phase transition,quantum phase transition,structural negative thermal expansion
更新于2025-09-04 15:30:14