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Volumetric radiative properties of irregular open-cell foams made from semitransparent absorbing-scattering media
摘要： This study aims to fully investigate the volumetric radiative properties of irregular open-cell foams made from semitransparent absorbing-scattering media such as ceramics. A Monte Carlo ray-tracing model was established in the limit of geometric optics to extract volumetric radiative properties of foams generated by a Voronoi tessellation technique. Three shape parameters for struts were proposed to mimic real struts. It was found that for extinction coefficient, the most influent parameters are porosity, mean cell diameter, and cross-sectional shape. For scattering albedo, it no longer depends on the surface reflectivity of solid struts but on the component radiative properties and strut shape parameters. Similarly, the scattering phase function no longer depends on the local reflection type but on an integrated contribution of the surface reflection, interface refraction, and volumetric radiation propagation inside the struts. The asymmetry factor is found closely related to the transparency of struts. Using the component radiative properties and structural parameters as input parameters, three analytical relations were established to respectively predict the extinction coefficients, scattering albedos, and asymmetry factors, which can be useful for the design and application of open-cell foams made from semitransparent media.
关键词： Analytical relation,Radiative property,Open-cell foam,Modified strut,Semitransparent ceramics
更新于2025-09-10 09:29:36
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Low-frequency dielectric dispersion in polymer-derived amorphous silicon carbonitride ceramics
摘要： Dielectric response of polymer-derived amorphous silicon carbonitride (PDC-SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Apart from presenting a relaxation process over 105–0.03 Hz frequency range, the material showed a strong low-frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC-SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC-SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4-x matrix and free-carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material.
关键词： polaron,polymer-derived ceramics,low-frequency dielectric dispersion,interfacial polarization
更新于2025-09-10 09:29:36
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Design for Highly Piezoelectric and Visible/Near-Infrared Photoresponsive Perovskite Oxides
摘要： Defect-engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B-site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point-defect-mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect-induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni2+-mediated (1–x)Na0.5Bi0.5TiO3-xBa(Ti0.5Ni0.5)O3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near-infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d33 = 151 pC N–1, Pr = 31.2 μC cm–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O3. This research provides a new paradigm for designing highly piezoelectric and visible/near-infrared photoresponsive perovskite oxides for solar energy conversion, near-infrared detection, and other multifunctional applications.
关键词： photovoltaics,ceramics,ferroelectrics,perovskite oxides,semiconductors
更新于2025-09-10 09:29:36
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Crystallization kinetics and the dielectric properties of SrO-BaO-Nb2O5-B2O3 glass-ceramics
摘要： Glass-ceramics materials of SrO-BaO-Nb2O5-B2O3 system have been prepared by conventional melt-casting followed by controlled crystallization. The crystallization kinetics, phase evolution, microstructure, breakdown strength and dielectric properties have been explored by differential scanning calorimetry (DSC), X-ray diffractometer (XRD), scanning electron microscope (SEM), and multifunction LCR meter. The results reveal that crystallization mechanism of this glass is believed to be three-dimensional interfacial growth. It was observed that predominant crystalline phase is Ba0.39Sr0.61Nb2O6 in these glass-ceramics crystallized at 750 °C, and the grain size increases with increase in crystallization time. The uniform microstructure can be seen clearly in glass-ceramics crystallized at 750 °C for 3 h, and the obtained glass-ceramics was found to possess optimal properties. Moreover, glass-ceramic with a dielectric constant of 58, the dielectric loss of 0.007 and breakdown strength of 1010 kV/cm could be achieved. In addition, energy storage density of glass-ceramics reached a maximal value of 2.62 J/cm3. To our knowledge, studies on SrO-BaO-Nb2O5-B2O3 glass-ceramics without SiO2 as a glass network former are few, and the melting temperature of the B2O3-based glass is lower than that of SiO2-based glass, which is conducive to the purpose of energy saving. These findings indicate that this glass may be a candidate for high energy-storage capacitors.
关键词： Energy storage density,Glass-ceramics,Crystallization,Dielectric properties
更新于2025-09-10 09:29:36
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Effect of Doped Sb2O3 on the Electrical Properties of TiO2-Based Ceramics with the Dual Function of a Varistor–Capacitor
摘要： TiO2-based varistor–capacitor ceramics co-doped with fixed Nb2O5, MnO2, Sm2O3 and various content of Sb2O3 are prepared, and then the effect of Sb2O3 on electrical properties of TiO2 varistor–capacitor ceramics is investigated. The results indicate that addition of Sb2O3 effectively decreases breakdown voltage (E1mA), while having less impact on the nonlinear coefficient (a). E1mA initially increases and then decreases with Sb2O3 increasing; contrarily, relative dielectric constant (er) decreases first and then increases. It is found that composition of 98.3%TiO2-0.8%Nb2O5-0.3%MnO2-0.3%Sm2O3-0.3%Sb2O3 is obtained with a low breakdown voltage of 2.3 V/mm, nonlinear coefficient of 2.0, high relative dielectric constant of 7.6 9 104 and low dissipation factor of 0.25, which is consistent with the narrowest grain boundary barriers in the composition. The nonlinear coefficient initially increases and then decreases with increase of Sb2O3; it reaches a maximum value of 2.9 at 0.2 mol.% Sb2O3, which is consistent with the highest grain boundary barriers in the composition. In order to explain the nonlinear current–voltage characteristics, a grain boundary defect barrier model was introduced.
关键词： grain boundary defect barrier model,Varistor ceramics,nonlinear properties,relative dielectric constant
更新于2025-09-10 09:29:36
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Yb3+/Tb3+/Ho3+: phosphate nanophase embedded glass ceramics: enhanced upconversion emission and temperature sensing behavior
摘要： Yb3+/Tb3+/Ho3+ tri-doped transparent phosphate glass–ceramics (GCs) were successfully synthetized by a conventional melt-quenching technique with subsequent glass crystallization. The formation of phosphate nanocrystals (NCs) with leucite structure was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected-area electron diffraction (SAED). The variation of the decay curves confirms the accumulation of active centers into the NCs lattice. Hence, the UC emission intensity of Yb3+/Tb3+/Ho3+ doped GC610 sample is greatly enhanced relative to that in precursor glass (PG). And the UC energy transfers processes were systematically analysis. The result shows that the energy transfer of Ho3+→Tb3+ exists while Yb3+ as a sensitizer ion. Furthermore, the temperature-dependent UC luminescence and temperature sensing behaviors of the prepared materials based on the thermally coupled levels of Tb3+: 5D4 and Ho3+: 5F5 in the temperature range of 298–648 K were systematically investigated, to explore its possible application as optical thermometric medium, by utilizing the fluorescence intensity ratio (FIR) technique. The relative sensitivity (Sr) of 7.5 × 10?3 K?1 and absolute sensitivity (Sa) of 22 × 10?3 K?1 are achieved in the Yb3+/Tb3+/Ho3+ tri-doped GC. This GC materials is a very promising candidate for optical temperature sensors.
关键词： Yb3+/Tb3+/Ho3+ tri-doped,phosphate glass–ceramics,upconversion emission,temperature sensing,optical thermometry
更新于2025-09-10 09:29:36
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Hydrothermal synthesis and characterization of In2O3-ZnGa2O4 nanocomposites and their application in IGZO ceramics
摘要： Poly-crystalline In2O3-ZnGa2O4 nanocomposites were successfully synthesized by hydrothermal method with a mixed solution of In, Ga and Zn nitrates with equal mole ratio (In: Ga: Zn=1: 1: 1) and the ammonia was used as the precipitant. The effects of hydrothermal temperature and pH value of the mixed solution on the properties of the nanocomposites were investigated. The microstructure of the prepared In2O3-ZnGa2O4 nanocomposites was characterized by SEM and TEM, respectively. The growth mechanisms of In2O3-ZnGa2O4 nanocomposites were also preliminarily discussed in this study. Results reveal that the IGZO ceramics prepared by In2O3-ZnGa2O4 nanocomposites own a high relative density of 99.5% and low resistivity of 1.2 mΩ·cm, which can be applied to the preparation of IGZO thin film with superior performance.
关键词： Nanocomposites,IGZO,Crystal structure,Ceramics
更新于2025-09-10 09:29:36
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Higher permittivity of Ni-doped Lead Zirconate Titanate, Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics
摘要： The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr0.52Ti0.48)O3] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0-20 at.%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597 cm-1, 608 cm-1, 611 cm-1, 605 and 613 cm-1 for Ni = 0, 5, 10, 15 and 20 at.%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε￠) & tand as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni = 5 at.%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (??max) decreased with an increase in doping concentration of Ni while the phase transition temperature increased with increase in doping concentration. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068 eV for x = 0.00 to x = 0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.
关键词： Piezoelectric ceramics,Dielectric,solid-state reaction,Ni-doping
更新于2025-09-10 09:29:36
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The effects of terbium oxide on phase transition and electronic properties of potassium-sodium niobate-based ceramics
摘要： Lead free piezoelectric ceramics 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3-xmol%Tb4O7 (KNNS- BNKZ-xTb4O7) are prepared by solid state reaction method. The effects of Tb4O7 on phase transition, grain growth and electronic properties of the ceramics are studied. Tb4O7 (x (cid:1) 0.2) induces a phase transition from tetragonal-orthorhombic coexistence phases to pseudo-cubic one. Meanwhile, Tb4O7 could reduce grain size and lead to step-like grain growth. In addition, Tb4O7 could enhance the temperature stability of KNNS-BNKZ ceramics. For pure KNNS-BNKZ ceramics, the d33* and kp are reduced by 68.0% and 24.3%, respectively, from 30 (cid:3)C to 150 (cid:3)C. For the component x ? 0.1, they are reduced by 6.1% and 1.6%, respectively, in the same temperature range. This paper may have positive signi?cance for searching lead free piezoelectric ceramics with excellent temperature stable properties.
关键词： Piezoelectric ceramics,Phase transition,Lead free,Temperature stability
更新于2025-09-10 09:29:36
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Enhanced energy storage properties of BaTiO3-Bi0.5Na0.5TiO3 lead-free ceramics modified by SrY0.5Nb0.5O3
摘要： In this work, a novel lead-free relaxor-ferroelectric ceramics of (1-x)(0.65BaTiO3-0.35Bi0.5Na0.5TiO3)-xSrY0.5Nb0.5O3 ((1-x)BTBNT-xSYN x ? 0.02e0.12), was designed and prepared by the conventional solid state reaction method. The results show that all of the sintered samples have a perovskite structure. The Curie Temperature (Tc) moves to the low temperature side which causes the high dielectric constant at room temperature, and the ferroelectric hysteresis loop becomes slimmer and slimmer with increasing the content of SYN. Meanwhile, the optimal energy storage properties can be obtained in 0.92BTBNT-0.08SYN ceramic with an impressive discharged energy density (Wrec) of 1.36 J/cm3 under 152 kV/cm, and the charge-discharge ef?ciency reaches 74.3%. Therefore, all these results indicate that (1-x)BTBNT-xSYN lead-free ceramics can be applied for pulsed power capacitors.
关键词： SrY0.5Nb0.5O3,Energy storage,Dielectric properties,Lead-free ceramics
更新于2025-09-10 09:29:36