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Nd3+ doped new oxyfluoro tellurite glasses and glass ceramics containing NaYF4 nano crystals ??1.06?μm emission analysis
摘要： Oxyfluoro tellurite glasses with chemical composition TeO2-ZnO-YF3-NaF (TZYN), doped with Nd3+ in different concentrations were prepared by the melt-quenching technique. Judd–Ofelt analyses of Nd3+ ions in the precursor glasses were performed to evaluate the phenomenological intensity parameters Ω2,4,6. From the NIR emission spectra, characteristic parameters such as effective band with (?λeff) and stimulated emission cross section (σP) were calculated for the three observed transitions, 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 and compared to other reported glasses. Based on the luminescence decay times of 4F3/2 excited state, the quantum efficiency was evaluated and it is highest for a 0.2 mol% Nd3+ doped glass (G-Nd2). Glass ceramics were obtained by controlled heat treatment of the glasses at 390oC for 5h (as determined by DSC), which is greater than the glass transition temperature Tg. Moreover, DSC results revealed that precipitation of the NdYF4 nanocrystalline phase (TC1) decreased with increasing Nd3+ concentration. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) investigations reveal that spherical NaYF4 nano-crystals are distributed homogeneously across the glassy matrix. The emission intensity of the 4F3/2→4I11/2 transition at 1.60 μm was enhanced in glass ceramics as compared to glasses because of the occupancy of the Nd3+ in NaYF4 nanocrystlline phase. The experimental lifetime value of 4F3/2 also enhanced from 124 to 187 μs from G-Nd2 glass to GC-Nd2 glass ceramic and decreased with increasing Nd3+ concentration.
关键词： Nd3+ doped,glass ceramics,1.06 μm emission analysis,NaYF4 nano crystals,oxyfluoro tellurite glasses
更新于2025-09-10 09:29:36
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Niobium oxynitride prepared by thermal NH3 nitridation as a photoanode material for solar water splitting
摘要： Niobium oxynitride (NbON) is a promising photoanode material for photoelectrochemical water splitting using visible light up to ~600 nm in wavelength. However, the NH3 nitridation method widely used for oxynitride synthesis cannot convert Nb2O5 (Nb5+) to crystalline NbON (Nb5+), due to the generation of NbOxNy (Nb2+-3+). To prevent Nb reduction during nitridation, we added O2 as an oxidant to the NH3 nitridation reaction system. Investigation of the relationship between O2 concentration and the crystal phase of the resulting samples revealed that Nb2O5 nitridation produces crystalline NbON (Nb5+) within a specific O2 concentration range. The O2 concentration required to synthesize NbON increases from 0.05% to over 0.40% upon increasing the nitridation temperature from 600 °C to 750 °C. The photoelectrochemical properties of NbON films were also investigated. Under simulated sunlight illumination, a NbON photoanode produced a photocurrent of 0.6 mA cm-2 at 1.2 V vs. RHE in H2O2 aqueous solution.
关键词： B. Optical properties,C. X-ray diffraction,D. Electrochemical properties,A. Nitrides,A. Ceramics
更新于2025-09-10 09:29:36
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Effect of Co Doping on Microstructures and Dielectric Properties of ZnO
摘要： Pure and Co-doped ZnO nanoparticles ( 2.5, 5, 7.5 and 10 at% Co) are synthesized by sol-gel method. The as-synthesized nanoparticles are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FE-SEM) analysis. The nanoparticles of 0, 2.5, 5at% Co doped ZnO exhibited hexagonal wurtzite structure and have no other phases. Moreover, The (101) diffraction peaks position of Co-doped ZnO shift toward smaller value of diffraction angle compared with pure ZnO powders. The results confirm that Co ions were well incorporated into ZnO crystal lattice. Simultaneously, Co doping also inhibited the growth of particles and the crystallite size decreased from 43.11 nm to 36.63 nm with the increase in doping concentration from 0 to 10at%. The values of the optical band gap Eg of all Co-doped ZnO nanoparticles gradually decreased from 3.09eV to 2.66eV with Co content increasing. Particular, the dielectric constant of all Co-doped ZnO ceramics gradually increased from 1.62×103 to 20.52×103, and the dielectric loss decreased from 2.36 to 1.28 when Co content increased from 0 to 10at%.
关键词： ZnO,Ceramics,Nanoparticles,Dielectric properties,Co-doping
更新于2025-09-10 09:29:36
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Improvement of electromechanical coupling coefficient in shear-mode of piezoelectric ceramics
摘要： Shear vibration mode of piezoelectric ceramic has been widely used in energy harvesting for its high electromechanical coupling coefficient (k15) and high piezoelectric constant (d15). In this study, the effects of dimensions on the piezoelectric shear performance of PZT-5A type ceramic were initially studied with ATILA/GiD finite element simulation to improve k15, and verified by experiments. We found out k15 dominantly correlates with the ratio of width to thickness, and dimension optimization was conducted for the first and high order shear vibrations. As a result, a maximum electromechanical coupling coefficient for k15 shear-mode reaching 0.612 was obtained in the first order harmonics. It is worth to note that the dimension ratio for optimized electromechanical coupling factor were in a similar scale regardless of the order of harmonics. In addition to the dimension optimization, the effect of mode coupling between shear vibration mode and unwanted mode was also investigated. The coupling between two vibrations did not only affect electromechanical coupling coefficient but also distorted resonance peak spectrum. Thus, the dimension ratios to avoid mode coupling was provided as the length should far away from the thickness. Finally, the effects of dimensions on mechanical quality factor were examined and the results were discussed. The mechanical quality factor will decrease when the mode coupling happens.
关键词： Electromechanical coupling coefficient,k15 shear-mode,Finite element analysis,Piezoelectric ceramics
更新于2025-09-10 09:29:36
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Influence of the ceramic powder morphology and forming conditions on the optical transmittance of YAG:Yb ceramics
摘要： The influence of the dispersity and morphology of ceramic powders on the characteristics of green bodies and the optical transmittance of YAG:Yb (20 at.%) ceramics was considered. The effect of the specific surface area on the relative density of compacts was studied. An increase in the specific surface area from 1.45 to 12.38 m2/g led to a decrease in the relative density of green body compacts from 52 to 38% under the fixed uniaxial pressure of 50 MPa. An increase in the uniaxial pressing value up to 150 MPa provided a maximum increase of the optical transmission of ceramics. However, an increase in the specific surface area and uniaxial pressure led to the appearance of macrodefects in ceramic samples. Cold isostatic pressing at 200 MPa after uniaxial pressing at 50 MPa resulted in an increase of optical transparency and the elimination of the macrodefect formation in ceramics. Dispersity and morphology of ceramic powders have a significant effect on the optical transparency of ceramics. Forming conditions had insignificant influence on optical characteristics. Highly transparent YAG:Yb ceramics with 80% transmittance were developed.
关键词： specific surface area,highly transparent YAG:Yb ceramics,agglomeration coefficient,forming,cold isostatic pressing
更新于2025-09-10 09:29:36
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Eu:Lu2O3 transparent ceramics fabricated by vacuum sintering of co-precipitated nanopowders
摘要： Europium doped lutetium oxide (Eu:Lu2O3) nanopowders were synthesized by a co-precipitation method using hydrogen carbonate (AHC) as a precipitant. Influence of the terminal pH value on properties of the Eu:Lu2O3 precursors and calcined powders was investigated. It is found that the terminal pH value has little influence on compositions of the precursors, and all the powders calcined at 1100 °C show good crystallinity. However, the terminal pH value has significant influence on morphology and agglomeration degree of both the precursors and the calcined powders. The powders are found to have the optimal dispersity with the average particle size of 68 nm when the terminal pH is 6.57. Using the nanopowders as starting materials, Eu:Lu2O3 transparent ceramics were fabricated by vacuum sintering at 1700 °C for 30 h. The ceramics prepared from the powders whose terminal pH is 6.57 were found to have the best transparency and the in-line transmittance reaches 68% at 611 nm. The influence of vacuum sintering temperatures on the microstructure and transmittance of the Eu:Lu2O3 transparent ceramics was also investigated. The Eu:Lu2O3 ceramics sintered at 1825 °C for 30 h show the highest in-line transmittance of 72% at 611 nm. The average grain size of the prepared Eu:Lu2O3 ceramics is about 454 μm and the light output of the sample is about 10 times higher than that of commercial BGO single crystal.
关键词： Vacuum sintering,Eu:Lu2O3 transparent ceramics,Terminal pH value,Co-precipitation method,Light yield,Microstructure
更新于2025-09-10 09:29:36
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Fabrication and magneto-optical properties of TGG transparent ceramics
摘要： Terbium gallium garnet (Tb3Ga5O12, TGG) transparent ceramics were synthesized by the co-precipitated method and vacuum sintering with MgO as sintering aids. Samples sintered at 1500℃, 1550℃ and 1600℃ for 20h were utilized to examine the phase compositions, optical quality, microstructure and magneto-optical property. X-ray diffraction (XRD) results show that the three samples have pure garnet crystal structure. The sample sintered at 1550℃ shows high transparency and the optical transmittance is close to 80% in the region of 500-1500 nm. SEM micrographs demonstrate that the sample sintered at 1550℃ exhibit best microstructure and the average grain sizes were 5.32 μm. The Verdet constant of the samples were investigated in detail at different wavelength and temperature. The results indicated that TGG ceramics can meet the demand for magneto-optical devices in the visible-near infrared region.
关键词： Faraday effect,Magneto-optical properties,TGG ceramics,Optical materials
更新于2025-09-10 09:29:36
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Site occupancy and electric-field induced strain response of Er-doped (Bi0.4Na0.4Sr0.2)TiO3 ceramics
摘要： Er-doped (Bi0.4Na0.4Sr0.2)TiO3 powders were prepared by solid state reactions according to A-site donor (Bi0.4-x/3Na0.4-x/3Sr0.2-x/3Erx)TiO3 (x ? 0.0.015 and 0.02) and B-site acceptor (Bi0.4Na0.4Sr0.2)Ti1-yEryO3 (y ? 0, 0.015 and 0.02) substitutional doping mechanisms. In both cases, room-temperature X-ray diffraction analyses revealed a decrease of the unit cell volume with increasing Er contents, suggesting A-site occupancy to be thermodynamically more favourable. Over the 25e175 (cid:2)C temperature range, A-site doped ceramics, in particular x ? 0.015, showed enhanced thermal stability of the maximum achievable electric-?eld induced strain. Importantly, this minor doping level also reduced dielectric loss at high temperature and led to a transition from non-ergodic to ergodic relaxor behaviour. These results may further motivate the study of the impact of other minor dopants in this family of Pb-free piezoceramics.
关键词： Erbium,Strain,Ceramics,Ferroelectric
更新于2025-09-10 09:29:36
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Computable translucency as a function of thickness in a multi-layered zirconia
摘要： Statement of problem. Determining the relationship between variable thicknesses and the translucency of dental ceramics is essential for optimizing esthetics in different clinical situations. Purpose. The purpose of this in vitro study was to analyze the relationship between layer thickness and translucency of 2 multi-layered monolithic zirconia materials and to develop an equation by which the grade of translucency can be calculated dependent on the materials’ layer thicknesses in advance. Material and methods. Two semisintered multi-layered zirconia blanks, namely KATANA Zirconia Super Translucent Multi-Layered Disk (Noritake Dental Supply Co, Ltd) and Zirconia Ultra Translucent Multi-Layered Disk (UTML) (Noritake Dental Supply Co, Ltd), were sectioned (N=96) to separate the 4 layers (n=12 per layer): enamel layer, transition layer 1, transition layer 2, body layer. All specimens were sintered in a furnace (M2 Plus; Thermo-Star) at 1500°C for 2 hours and automatically polished under water cooling up to P2400 for the thicknesses of 1.6, 1.3, 1.0, 0.7, and 0.4 mm. Transmittance of visible light was measured using a spectrophotometer (Lambda 35; Perkin Elmer). Data were analyzed using the Kolmogorov-Smirnov, 2-way ANOVA, and Scheffé post hoc tests (a=.01) and curve fitting. Results. Analyzing the fitting of the values of the 8 material groups to the linear, exponential, and logarithmic curves, 7 of the 8 groups (not UTML body layer) fitted the most (R-square value closer to 1.0) to the logarithmic curve. Constants were obtained from the distance to the x-axis and the curvature. Conclusions. The methodology of this study provided the materials’ specific constants a and b by analyzing the translucency behavior of KATANA Super Translucent Multi-Layered Disk and Ultra Translucent Multi-Layered Disk in different thicknesses, allowing further translucency calculation by applying the developed formula and the constants.
关键词： zirconia,translucency,thickness,esthetics,dental ceramics
更新于2025-09-10 09:29:36
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Determination of polaronic conductivity in disordered double perovskite La2CrMnO6
摘要： Double perovskite La2CrMnO6 ceramics was sintered using standard high temperature route in ambient air. The orthorhombic Pbnm cell characterized by a total disorder between Cr and Mn ions was determined using an XRD powder test. The grain morphology, porosity and chemical composition were determined using scanning electron microscopy. The X-ray photoemission spectroscopy showed several contributions to O 1 s, La 3d, Mn 2p, and Cr 2p core lines related to the occurrence of multiple ionic states. The electrical permittivity, modulus, AC and DC conductivity were measured in ranges of f = 20 Hz – 1 MHz and 76–440 K. The electrical transport mechanism was attributed to the small polarons. The nearest neighbor hopping occurred in the range 170 to 440 K. The variable range hoping, attributed to the Fermi glass features and disorder, was detected in the range 100 to 160 K. The relaxation process related to the temperature-independent activation energy was deduced from the electric modulus scaling.
关键词： La2CrMnO6 ceramics,Sintering,Electrical properties,Solid state synthesis
更新于2025-09-10 09:29:36