Ceramics International最新文献

By adopting the solid-state reaction method, rare-earth-based NaSrRE (WO₄)₃ (RE = Ce, Nd, Sm) ceramics were successfully synthesized. The investigation also focused on the relationship between the microstructure and microwave dielectric properties. X-ray diffraction (XRD) results indicated that NaSrRE (WO₄)₃ ceramics exhibit a tetragonal scheelite structure with a space group of I4₁/a. It was found that the incorporation of smaller rare earth ions leads to a reduction in cell volume. The NaSrCe(WO₄)₃ ceramics sintered at 1250 °C exhibited excellent dielectric properties with ε_r = 8.84, Q×f = 73128 GHz, τ_f = -47.17 ppm/°C, the NaSrNd(WO₄)₃ ceramics sintered at 1225 °C showed dielectric properties of ε_r = 9.14, Q×f = 47824 GHz, τ_f = -55.56 ppm/°C, and the NaSrSm(WO₄)₃ ceramics sintered at 1225 °C demonstrated excellent dielectric properties with ε_r = 9.31, Q×f = 69141 GHz, τ_f = -46.99 ppm/°C. In general, the incorporation of rare earth ions of varying sizes at the A site of the scheelite structure can enhance the dielectric properties of the ceramics to some extent.

The FeTiO3 nanopowder is a vital engineering material known for its exceptional performance in energy generation, storage, electrochemical sensors, and catalysis. However, synthesizing FeTiO3 nanopowder with high crystallinity and phase purity typically requires specialized equipment and controlled heat treatment due to the instability of Fe2+ ions. Using the one-step solution combustion synthesis (SCS) method, FeTiO3 nanopowder withe high crystallinity were successfully produced utilizing basic equipment. Additionally, the influence of carbon additives on phase transitions, as well as the physical and physicochemical properties of the synthesized powder, was examined. XRD results indicate that increasing the amount of fuel, particularly glycine, creates a stable environment for the crystallization of FeTiO3 nanoparticles. Moreover, enhancing the carbon content in precursor solutions with urea enhances reduction conditions and boosts the stability of FeTiO3 in the final product. The presence of carbon additives in glycine-fuel samples leads to unfavorable outcomes by increasing the levels of TiO2 and Fe3O4 undesirable phases. Incorporating additive carbon into the urea-synthesized precursor solution resulted in a particle size increase exceeding 50 nm and raised the combustion temperature by a minimum of 230 °C. Furthermore, the presence of 15 wt.% additive carbon in the sample synthesized with glycine improved the specific surface area of particles from 2.44 m2/g to 18.41 m2/g. Obtained results have shown that achieving high crystallinity of FeTiO3 nanopowder is feasible through a one-step solution combustion synthesis process. This can be accomplished by carefully choosing the synthesis conditions, such as the type and quantity of fuel, along with the carbon additive.

The holmium (Ho³⁺) ions-based fluoro borosilicate (SBNCHo) glasses have been prepared using the traditional melt quenching technique with varying concentrations of Ho³⁺ ions. Physical parameters were analyzed using x-ray diffraction, energy dispersive analysis of x-rays, fourier transform infrared spectroscopy, optical, luminescence, and Commission International de I’Eclairage (CIE) studies. Judd-Ofelt spectral intensity parameters were evaluated for SBNCHo_10 (Ω₂ = 5.292 x 10^-20 cm², Ω₄ = 3.062 x 10^-20 cm² and Ω₆ = 3.376 x 10^-20 cm²) glass, optical bandgaps were estimated using optical absorption studies. The Photoluminescence emission spectra were recorded for synthesized glasses with 452 nm excitation. The stimulated emission (σ_e = 1.40 x 10^-20 cm²) for the intense green radiation (⁵S₂ (⁵F₄) → ⁵I₈) was calculated. The lifetime decay profile was analyzed for all the synthesized glasses. From the CIE color coordinates of SBNCHo glasses, the color purity was estimated to be (SBNCHo_10 (98.6%)). These results strongly support the applicability of SBNCHo_1.0 glass for green laser applications.

The preparation of Si₃N₄ ceramics by vat photopolymerization (VPP) has motivated increasing research interest. However, it is challenging to prepare Si₃N₄ ceramics by VPP due to the high UV-light absorbance and refractive index of powder. In this paper, a method for Al₂O₃-coated Si₃N₄ powder was proposed. Combined with the boehmite-coated and high-temperature treatment, Al₂O₃ was successfully coated on the surface of Si₃N₄ powder. The effect of Al₂O₃ content on the properties of Si₃N₄ powders, slurry and the sintered Si₃N₄ samples were investigated. The Al₂O₃ coating layer not only improves the curing forming ability of Si₃N₄ slurries, but also can directly act as one of the sintering aids of Si₃N₄ ceramics. The bulk density of the samples decreases from 3.04 ± 0.02 g/cm³ to 2.97 ± 0.01 g/cm³ with the increase of coating content, while the porosity increases from 5.38 ± 0.89 % to 7.54 ± 0.63 %. The sample of 5 wt % Al₂O₃ coating content has the maximum flexural strength of 474.28 ± 16.38 MPa and the highest relative density of 94.62 ± 0.89 %. This work can not only obtain a great modification effect, but also promote the dense sintering of Si₃N₄ ceramics during subsequent stages, which provides a constructive method for modifying Si₃N₄ powders to achieve photopolymerization.

This research investigates the effects of barium (Ba) doping the photoelectric properties of zinc oxide (ZnO) nanoparticles (NPs) to explore their potential applications in optoelectronic devices.Photocurrent experiments reveal intriguing negative photoconductivity (NPC) behavior in Ba:ZnO based UV photodetectors (PDs).Moreover, the exploration of UV PD performance reveals rise and fall times of approximately 8.26s and 8.72s, respectively, under a -1V external bias.Our fabricated device shows higher detectivity about $$ Jones and external quantum efficiency exceeding 100%, compared to other PD. The analysis of transient currentsuggests the existence of two kinds of defects contributing to NPC. Through an investigation of the noise density, exponents γ ranging between -2.048 and -1.76 were determined, substantiating the hypothesis that the observed noise originates from a distribution of defects. Overall, these results underscore the potential of Ba:ZnO NPs for high-performance devices compared to conventional ZnO-based PDs.

BaTiO₃/Ca₁₀(PO₄)₆(OH)₂ composite ceramic is an outstanding representative of piezoelectric biomaterials, with excellent biocompatibility and piezoelectric effect, and has potential applications in the field of bone tissue repair. In this work, vat photopolymerization 3D printing technology was used to fabricate triply periodic minimal surface structure BaTiO₃/Ca₁₀(PO₄)₆(OH)₂ composite ceramic bone tissue scaffolds with different pore sizes and porosity, and their mechanical and electrical properties were studied. First, the ceramic slurry configuration process was optimized to obtain a ceramic slurry with high solid content (45 vol%) and excellent rheological properties. Then the effect of sintering temperature on microstructure, relative density, mechanical properties, and electrical properties is discussed. The results show that when sintering at 1300 °C, the BaTiO₃/Ca₁₀(PO₄)₆(OH)₂ composite ceramic has the highest relative density (99.18%), the highest compressive strength (44 MPa), large relative dielectric constant (379–389), and low dielectric loss. The polarization electric field strength of the BaTiO₃/Ca₁₀(PO₄)₆(OH)₂ composite ceramic was set to 15 kV/cm through the test of the hysteresis loop. Finally, based on multi-physics coupled finite element simulation, the effects of different porosity and different pore sizes on stress distribution and piezoelectric potential were analyzed, and the relationship between them was explored through experiments. The results show that as the porosity increases and the pore size decreases, the mechanical properties of the scaffold decrease significantly, and its compressive strength ranges between 1.67–4.26 MPa; as the porosity increases and the pore size increases, the piezoelectric coefficient (d₃₃) of the scaffold showed a decreasing trend, and its d₃₃ ranged between 2–9 pC/N. The mechanical and electrical properties of the scaffold meet the performance requirements of cancellous bone. In summary, this work provides a strategy for the application of customized BaTiO₃/Ca₁₀(PO₄)₆(OH)₂ composite ceramic scaffolds in new-generation orthopedic implants.

Lithium-aluminum-zinc phosphate glasses doped with thulium and dysprosium ions are characterized by using spectroscopy techniques. The Judd-Ofelt parameters were evaluated to calculate the radiative parameters of thulium ¹D₂ $$³F₄ and ¹G₄ $$³H₆ visible transitions and ³H₄ $$³F₄ near infrared transition, which shows the highest optical amplification parameters. Upon 356 nm excitation, the Tm³⁺ doped phosphate glass emits blue light with CIE1931 chromaticity coordinates x = 0.1540 and y = 0.0283 and color purity around 96.8%. With excitations at 347 and 350 nm, the Dy³⁺/Tm³⁺ doped phosphate glass emits neutral and cold white light with correlated color temperature values of 4716 and 6628 K, respectively. The dysprosium emission decay time in the codoped glass is shorter than that in the Dy³⁺ single-doped glass, indicating a non-radiative energy transfer from Dy³⁺ to Tm³⁺. The dominant electrical interaction involved in the energy transfer, following the model Inokuti-Hirayama, is of dipole-dipole type. The energy transfer probability and efficiency are 769.0 s^-1 and 0.53, respectively. Tm³⁺ doped and Dy³⁺/Tm³⁺co-doped lithium-aluminum-zinc phosphate glasses could be appropriate for blue and neutral/cold white light-emitting device applications.

Porous Si₃N₄ ceramics are widely applied in aerospace and mechanical fields owing to their excellent properties. Furthermore, vat photopolymerization (VPP) technology can fabricate Si₃N₄ components with complicated structures and high precision, but its layer-by-layer printing method leads to poor mechanical properties of ceramics. In this study, porous Si₃N₄ ceramics with a porosity of 28.41% strengthened by directional β-Si₃N₄ were fabricated by combining VPP technology and seeding method. Rheological behavior and curing properties of the slurry were explored, and the influence of β-Si₃N₄ content on the mechanical properties of printed Si₃N₄ ceramics was investigated systematically. With the increase of β-Si₃N₄ content, the orientation degree of β-Si₃N₄ grains increased gradually, while fracture toughness and flexural strength of the ceramics exhibited a trend of increased first and then decreased and Vickers hardness gradually decreased. As β-Si₃N₄ content increased to 5 wt%, the fracture toughness and flexural strength of porous Si₃N₄ ceramics were improved from 4.23 MPa·m^1/2 and 214.7 MPa to 5.65 MPa·m^1/2 and 272.0 MPa, respectively. Therefore, this work indicates that vat photopolymerization combined with seeding method is a promising approach for the fabrication of porous Si₃N₄ ceramics with high performance and complex structures.

Al₂O₃ with the desired electrical insulating properties and thermal shock resistivity has been extensively applied in the field of solid oxide fuel cells and oxygen sensors. However, degradation of the insulating Al₂O₃ layer is an intractable issue in practical applications. In this study, different point defect structures of Al₂O₃ were realized with the substitutional doping effect of ZrO₂ and MgO. The MgO dopant provides positively charged oxygen vacancies, whereas the ZrO₂ dopant tends to trigger negatively charged vacancy formation at Al³⁺ sites. The oxygen vacancy concentration of Al₂O₃ exhibits the following trend: MgO-doped Al₂O₃ > Al₂O₃ > ZrO₂-doped Al₂O₃. Furthermore, the densification morphology, insulating properties, and oxygen vacancy migration of Al₂O₃ have been confirmed to be largely affected by the extrinsic factors. This study indicates that oxygen vacancy migration depends on the applied electric field at high temperatures. As the voltage and temperature increase, oxygen vacancy migration shows obvious electric-field-dependent characteristics, and its aggregation macroscopically shows hole defects. The defect position of Al₂O₃ is nonstoichiometric Al₂O_3-x with poor crystallinity. Therefore, it is believed that the oxygen vacancy migration triggered by the second phase directly determines the insulation performance and causes the degradation of Al₂O₃ materials.

This study delves into the influence of TiN and NbC ceramic particles on the phase structure, grain organization, microhardness, and wear resistance of FeCoNiCrAl High-Entropy Alloy (HEA) composite coatings produced through laser cladding. The integration of ceramic particles induced a dual BCC solid-solution phase structure (B2+BCC), with the formation of a TiNb phase upon the melting and interaction of TiN and NbC in the melt pool. The ceramic particles significantly modified the grain structure of the HEA coatings, disrupting the Columnar-to-Equiaxed Transition (CET) and favoring the emergence of equiaxed grains. The TiN particles induced a substantial refinement of grain size, albeit unevenly, while NbC had a milder effect. The combined presence of TiN and NbC particles resulted in a more uniform grain refinement, enhancing the mechanical properties of the coatings. Notably, the (TiN+NbC)/HEAs composite coating demonstrated superior mechanical performance under the synergistic effect of both ceramic particles. The average microhardness value increased by 55.80% compared to 17-4Ph stainless steel, and the wear rate was reduced by 88.38%, with the wear mechanism primarily involving abrasive and oxidative wear.