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Dielectric and photoluminescence properties of fine-grained BaTiO <sub/>3</sub> ceramics co-doped with amphoteric Sm and valence-variable Cr
摘要： Dielectric and photoluminescence properties of fine-grained BaTiO3 ceramics co-doped with amphoteric Sm and valence-variable Cr (Ba1-xSmx)(Ti1-xCrx)O3 (BSTC) and (Ba1-xSmx)(Ti1-(x-0.01)Crx-0.01)O3 (BSTC1) ceramics with a single-phase perovskite structure were prepared using a traditional solid state based method. The structure, microstructure, site occupations, valence states of Cr, photoluminescence, and dielectric properties of these ceramics were investigated using XRD, SEM, EDXS, RS, EPR, XPS, and dielectric measurements. All ceramics exhibit a fine-grained microstructure (0.7 mm). Three valence states of Cr ions were confirmed and Cr predominates as Cr3+ enter the Ti4+ sites with a stronger EPR signal (1.974). The RS bands of high-wavenumber were attributed to photoluminescence from Sm3+ ions. The formation of SmBa?-CrTi' defect complexes play leading roles in the removal of VO??, prevent the grain growth, and photoluminescence quenching. (Ba1-xSmx)(Ti1-(x-0.01)Crx-0.01)O3 (BSTC1) ceramics with amphoteric Sm3+ ions exhibit a regular diffuse phase transition behavior, rapid Tm-shifting rate of -24.3 °C/at% (Sm/Cr), higher εRT; lower tan δ and x = 0.04 and 0.05 met the EIA Y5V specification.
关键词： Sm and Cr doping,BaTiO3 ceramics,photoluminescence,dielectric properties,co-doping
更新于2025-09-19 17:15:36
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Linear-like lead-free relaxor antiferroelectric (Bi0.5Na0.5)TiO3-NaNbO3 with giant energy-storage density/efficiency and super stability against temperature and frequency
摘要： A novel lead-free polar dielectric ceramic with linear-like polarization responses was found out in (1-x)(Bi0.5Na0.5)TiO3-xNaNbO3 ((1-x)BNT-xNN) solid solutions, exhibiting giant energy storage density/efficiency and super stability against temperature and frequency. High-resolution transmission electron microscopy, Raman scattering and Rietveld refinements of x-ray diffraction data suggest that these property characteristics be derived from temperature and electric field insensitive large permittivity as a result of relaxor antiferroelectricity (AFE) with polar nanoregions. Additionally, this feature intrinsically requires high driving field for AFE to ferroelectric (FE) phase transitions due to large random fields. Measurements of temperature-dependent permittivity and polarization versus electric field hysteresis loops indicate that high-temperature AFE P4bm phase in BNT was gradually stabilized close to room temperature, accompanying a phase transition from relaxor rhombohedral FEs to relaxor tetragonal AFEs approximately at x=0.15-0.2. A record high for recoverable energy-storage density W~7.02 J/cm3 as well as a high efficiency η~85% was simultaneously achieved in the x=0.22 bulk ceramic, which challenges the existing fact that W and η must be seriously compromised. Furthermore, desirable W (?3.5 J/cm3) and η (?88%) with a variation of less than 10% can be accordingly obtained in the temperature range of 25-250 oC and frequency range of 0.1-100 Hz. These excellent energy-storage properties would make BNT-based lead-free AFE ceramic systems be a potential candidate applied for pulsed power systems.
关键词： Relaxor antiferroelectric,Dielectric,Energy storage,Polar nanoregions,Lead-free ceramics
更新于2025-09-19 17:15:36
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MgF2-Based Luminescing Ceramics
摘要： Results of investigation at 300 K of photo- and cathodoluminescence of the high-temperature optical ceramics synthesized for the first time based on MgF2 activated tungsten oxide are presented.
关键词： luminescence,tungsten,ceramics,magnesium fluoride,excitation spectra,annealing
更新于2025-09-19 17:15:36
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Influences of the Sc3+ content on the microstructure and optical properties of 10?at.% Yb:Y3ScxAl5-xO12 laser ceramics
摘要： 10 at.% Yb:Y3ScxAl5-xO12 (x=0.25, 0.5, 1.0 and 1.5) transparent ceramics have been successfully fabricated by the solid state reaction method combined with vacuum sintering, whose transmittances reach 80% at 1100 nm with thickness of 3.0 mm. The full width at half maximum (FWHM) of the emission peaks located at about 1030 nm increases for increasing the Sc3+ content, and a maximum FWHM of 14.53 nm is obtained for 10 at.% Yb:Y3Sc1.5Al3.5O12 ceramics, which is 1.4 times larger than that of the 10 at.% Yb:Y3Al5O12 (Yb:YAG) ceramics. Finally, the laser performance of the 10 at.% Yb:Y3Sc1.5Al3.5O12 ceramics was tested and compared with that of a standard 10 at.% Yb:YAG sample. In quasi continuous wave (QCW) regime, a maximum laser output power of 10.8 W was obtained with the slope efficiency of 66.4%. The tuning range significantly broadens in the case of the Yb:YSAG sample, reaching a width of 86.2 nm.
关键词： Laser ceramics,Microstructure,Yb:Y3ScxAl5-xO12,Optical properties
更新于2025-09-19 17:13:59
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Fabrication of Er:Y2O3 transparent ceramics for 2.7?μm mid-infrared solid-state lasers
摘要： Laser grade 7 at.% Er:Y2O3 transparent ceramics with submicron grain size were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. Through studying the sintering trajectory of Er:Y2O3 ceramics, the sintering temperature zone where sufficient relative density (> 96%), no pore-boundary separation, and sub-micron grain size (< 1 μm) ceramic samples could be identified. The samples pre-sintered in this zone were readily densified by HIPing. To maximum the densification and achieve high transparency, it is critical to suppress the final-stage grain growth. After HIPing at 1520 °C, the Er:Y2O3 ceramics were fully densified without further grain growth, and exhibited in-line transmission of about 81.6% at 2000 nm. Continuous wave (CW) room temperature laser operation of the Er:Y2O3 transparent ceramic at 2.7 μm was demonstrated.
关键词： Transparent ceramics,Microstructure,Mid-infrared,Solid-state lasers
更新于2025-09-19 17:13:59
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Laser Micro-Texturing of Sintered Tool Materials Surface
摘要： The purpose of this paper is to show the effect of tool materials surface treatment while using laser texturing on the structure and properties of cemented carbides and sialon ceramics. The tests were made on multi-point inserts subjected laser texturization and honeycomb-like texture was obtained. Comprehensive investigations in the scanning electron microscope (SEM) were made. Morphology was examined by the use of atomic forces microscope (AFM) and confocal microscope. The chemical composition of the tested materials using energy-dispersive X-ray spectrometer (EDS) was investigated. Moreover, exploitative properties, including wear resistance using the "pin on disc" method and roughness, were also tested. It was found that the laser texturing provides a suitable modification of the structure improving tribological properties. Tests suggest that laser texturing can contribute to the durability of cutting tool’s edge, which qualifies this type of surface treatment for wide industrial applications.
关键词： Laser Induced Periodic Surface Structures (LIPSS),cemented carbides,laser texturing,sialon tool ceramics
更新于2025-09-19 17:13:59
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Fabrication of grooves on polymer-derived SiAlCN ceramics using femtosecond laser pulses
摘要： In this study, grooves were fabricated on the surface of fully dense polymer-derived SiAlCN ceramics. Industrial femtosecond laser source was used at wavelength of 1030 nm with pulse duration of 290 fs and repetition rate of 100 kHz. Moreover, comprehensive study was carried out to evaluate the influence of scan speed and energy fluence on grooves quality, including the heat-affected zone around the laser-machined grooves, microstructures of laser-irradiated surface, and cross-section morphology of grooves. A series of grooves with width in the range of 30–80 μm and depth below 280 μm was successfully fabricated using femtosecond laser pulse. Laser parameters were optimized to obtain grooves with satisfying surface quality. Furthermore, formation and disappearance of laser-induced periodic surface structures were systematically investigated. This study proposes fabrication of grooves on SiAlCN ceramics via laser processing, which provides precise method for fabrication of microstructure with fascinating properties.
关键词： Laser-induced periodic surface structures,Polymer-derived ceramics,Femtosecond laser pulse,Groove
更新于2025-09-19 17:13:59
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Dynamics of Yb2+ to Yb3+ ion valence transformations in Yb:YAG ceramics used for high-power lasers
摘要： Due to the good thermal-mechanical and luminescence properties, Yb:YAG ceramics are suitable as thin-disk lasers; however, their efficiency is limited by the presence of Yb2t ions, which entail parasitic energy transfer from Yb3t formation in Yb:YAG ceramics prepared by solid-state reaction sintering. The samples were prepared by air annealing, the oxidation of the material leads to recharging Yb2t ion to its trivalent state. The activation energy was determined by Jander to be Ea(D) ? 2.7 ? 0.2 eV, which is in good agreement with the activation energy for oxygen diffusion in the YAG lattice. It was concluded that the recharging of Yb2t ion to its trivalent state in YAG ceramics is limited by the oxygen self-diffusion through the grain volume, and the oxygen vacancy alone and/or together with the presence of antisites can be proposed as Yb2t charge compensation mechanism in the YAG ceramics, unlike the YbAG single crystals, where tetravalent impurities are responsible for charge compensation.
关键词： Yb:YAG,Optical ceramics,Oxidation kinetics
更新于2025-09-19 17:13:59
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Strain Improving the Performance of a Flexible Monolayer MoS <sub/>2</sub> Photodetector
摘要： Electromagnetic wave absorbing foamed ceramics (FCs) with high closed porosity and gradient SiC distribution were prepared from the powder blend containing quartz, talc, CaCO3, Si3N4 and SiC by sintering at 1200 °C for 1 h in air. The retention in the temperature holding process of the continuous and gradual SiC distribution arising from the inward oxidation of SiC in the temperature rising process is the formation mechanism of the gradient SiC distribution in FCs. As to the FC prepared from the powder blend with 3 wt% of SiC, it shows the best comprehensive performance with low bulk density of 0.48 g/cm3 and relatively high compressive strength of 9.6 MPa, good thermal insulation performance for its high total porosity of 82%, good water resistance performance for its high closed porosity of 80%, and excellent electromagnetic wave absorption performance for its low mean re?ectivity of ?11.9 dB in the frequency range of 8.0–18.0 GHz and especially low minimum re?ectivity of ?14.2 dB at 12.7 GHz. More importantly, it is also an excellent high temperature electromagnetic wave absorbing material for its little increased mean re?ectivity of ?11.3 dB after heat treating at 1000 °C for 20 h in air.
关键词： Electromagnetic wave re?ectivity,High closed porosity,Electromagnetic wave absorption performance,Foamed ceramics,Gradient distribution
更新于2025-09-19 17:13:59
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Unique Design Strategy for Laser‐Driven Color Converters Enabling Superhigh‐Luminance and High‐Directionality White Light
摘要： Robust ceramic color converters withstanding strong laser irradiations have recently drawn great attention for laser-driven white lighting. However, the local emission within the incident laser spot usually expands to the whole surface area of the ceramics, which definitely makes it hard to achieve white light with high luminance and high directionality. Herein, a new strategy is proposed to solve the problem by elaborately introducing uniform spherical pores (diameter of ≈2 μm) into the phosphor ceramics with controlled contents from 8 to 24.6 vol%. The well-distributed pores, acting as light scattering centers, enable reduction of the luminescent spot size greatly but without any losses in conversion efficiency. By using the high-scattering ceramic color converters with 15% porosity, the light spot diameter is decreased by 46% and the central illuminance is increased by 156%. Moreover, laser-driven white light with an enhanced beam directionality and uniformity is also achieved. A superhigh luminous flux of 7199 lm is realized by using this promising color converter in a rotary mode. The designed high-scattering ceramics with controllable microstructures show great potential for use in extra-high luminance laser-driven lighting and projection.
关键词： light confinement,phosphor ceramics,phosphor wheel,laser-driven lighting,color converters,scattering
更新于2025-09-19 17:13:59