Effects of structural phase changes on the luminescence of Eu-doped (1-x)BaTiO3-xCaZrO3

We investigated the structural and luminescent properties of Eu³⁺-doped (1-x)BaTiO₃-xCaZrO₃ (BCTZ:Eu). The changes in the structural symmetry of BCTZ:Eu with CaZrO₃ substitution and Eu³⁺ doping was determined using Rietveld refinement of the X-ray diffraction patterns. Under ultraviolet photoexcitation, the specimens exhibited typical red-orange emission peaks resulting from the f–f transitions from Eu³⁺ ions. The intensities and asymmetry ratios of the emission intensities, as well as Stark splitting of the emission bands from Eu³⁺ were found to be strongly dependent on the structural phase transformation of BCTZ from tetragonal to rhombohedral. These findings suggest that BCTZ:Eu possesses a great potential for multifunctional devices that have both ferroelectric and luminous properties.     

Evaluation of mechanical properties of YSZ TBCs doped by different ratios of Eu3+ ions after isothermal oxidation

Thermal barrier coatings (TBCs) are essential to improve the thermal insulation performance of high-temperature components. Rare earth element (Eu³⁺) doped yttrium stabilized zirconia (YSZ) TBCs have been proved to be an ideal solution for non-destructive testing of internal damages. Based on this theory, two types of coatings deposited by air plasma spray (APS) on Hastelloy-X were investigated: (1) Eu³⁺ doped YSZ (dopant ratios 1 mol%, 2 mol%, 4 mol%, respectively), (2) traditional undoped 8YSZ. Isothermal oxidation treatment at 1100 °C, in increments of 10h until the failure of the coatings are conducted to evaluate the mechanical properties of different coatings. The microscopic morphology and phase of the coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) patterns, respectively. The indentation testing methods were used to study the apparent interfacial fracture toughness and the hardness of the ceramic top coat. Results show that the Vickers hardness of the top coat increases with the decrease of porosity in the early stage and then decreases with the heat treatment time increasing in the long-term stage. Simultaneously, compared with the undoped 8YSZ coating, the fracture toughness increased with the dopant of Eu³⁺ ions increasing, from 1 mol% to 2 mol%, nevertheless, that of 4 mol% Eu³⁺ doped YSZ decreased compared with in the undoped 8 YSZ. For all types of specimens, the interfacial fracture toughness decreases with the increase of isothermal oxidation time. Results also indicate that the content of Eu³⁺ doping does not affect the microstructure and interfacial morphology of the YSZ coating as well as the growth law of thermally grown oxides (TGO). Furthermore, EDS detection found that the Eu³⁺ ions almost do not diffuse inside the TBCs system after isothermal oxidation treatment.     

Oxygen-ion conductivity and mechanical properties of Lu2O3-doped ZrO2 as a solid electrolyte

The characteristics of Lu₂O₃-doped ZrO₂ as a solid electrolyte material were investigated in terms of its oxygen ion conductivity and flexural strength to realize its electrolytic function at intermediate and high temperatures. The effect of doping Lu³⁺, which has a high nuclear charge electric field strength, was examined through impedance spectroscopy, open-circuit potential measurements, and bending tests. The results with Lu₂O₃ dopant were compared with those obtained with a widely used dopant, Y³⁺, having a similar ionic radius with Lu³⁺, as well as a dopant that provides high ionic conduction, Sc³⁺, having a smaller ionic radius with Zr⁴⁺. The results revealed that, at the same dopant concentration, both the ionic conductivity and the flexural strength of Lu₂O₃-doped ZrO₂ are higher than those of the widely used Y₂O₃-doped ZrO₂. The conductivity of 8 mol% Lu₂O₃-doped ZrO₂ surpassed that of 8 mol% Sc₂O₃-doped ZrO₂ in the range of 800–950 °C (0.153 S/cm vs. 0.121 S/cm at 900 °C). These results indicate the potential of Lu³⁺ as a dopant for enhancing the performance of ZrO₂ solid electrolytes.     

Room-temperature densification of MgO bulk ceramics with dispersed nitride phosphor particles

Wave conversion materials with high thermal conductivity are necessary for high-power semiconductor lighting. Ceramics have higher thermal conductivity than existing matrices such as resin or glass in which phosphor particles are dispersed. However, the high densification of ceramics generally requires high-temperature sintering, which degrades and alters the phosphor particles. In this study, we aimed to achieve the high densification of MgO ceramics at room temperature. Applying high hydrostatic pressure with water addition improved the sample packing ratio and promoted the formation of Mg(OH)₂. As a result, the relative density was ≥95%. Additionally, various nitride phosphor particles (CaAlSiN₃:Eu²⁺, β-SiAlON:Eu²⁺, and α-SiAlON:Eu²⁺) were dispersed in the MgO matrix at room temperature without degrading the luminescence property. The thermal conductivity of the obtained sample was about 8 W m^?1K^?1, 40 times higher than that of the epoxy matrix.     

Migration,transformation and solidification/stabilization mechanisms of heavy metals in glass-ceramics made from MSWI fly ash and pickling sludge

In consideration of recycling solid waste to achieve high value-added products, glass-ceramics have been fabricated from municipal solid waste incineration (MSWI) fly ash, pickling sludge (PS), and waste glass (WG) by melting at 1450 °C firstly to achieve parent glass and then crystallizing at 850 °C. Results demonstrated that heavy metals have been well solidified in the prepared glass-ceramics, and relatively/extremely low leaching concentrations of heavy metals have been detected. The synthetic toxicity index of heavy metals has been greatly reduced from 7-18 to <3.2 after crystallization treatment, and the leaching concentrations of Cr, Ni, Zn, Cu, and Pb are 0.15, 0.05, 0.26, 0.12, 0.19 mg L^-1 respectively. Chemical morphology analysis, principal component analysis, TEM and EPMA were utilized to clarify the migration, transformation, and solidification mechanism of heavy metals from the as-received solid wastes. The major heavy metals, Cr and Ni which is responsible for the most toxicity, mainly exist in form of the oxidation state and residual state in parent glass, while the residual state in the glass-ceramics. The solidification performance was mostly positively correlated with the form of residue state, which the stability of heavy metals in glass-ceramics is improved. The solidification mechanism of heavy metals in glass-ceramics could be explained by the combination of chemical solidification/stabilization and physical coating. The TEM and EPMA confirmed that Cr and Ni mainly exist in the spinel crystalline (NiCr₂O₄, Fe_0.99Ni_0.01Fe_1.97Cr_0.03O₄) by solid solution or chemical substitution, and a small amount of Cr in the diopside phase. Pb, Cu, and Zn are homogenously dispersed in the glass-ceramics, which is considered as physical coating solidification.     

Preparation of spherical and porous strontium titanate particles by hot water and hydrothermal conversion of hydrous titania

Uniform, micron-sized SrTiO₃ particles do not tend to aggregate, and the low surface area of larger particles can be improved by incorporating porous structures, thus offering superior performance for a range of applications. In this study, submicron-to micron-sized SrTiO₃ particles were prepared using hot water or hydrothermal conversion of spherical hydrous titania (TiO₂·nH₂O) and porous hydrous titania. When spherical hydrous titania particles were employed as the starting material, spherical SrTiO₃ particles of hydrous titania were obtained via treatment at 120 °C for 24 h. Similarly, the use of porous hydrous titania particles treated at 90 °C for 48 h resulted in spherical porous SrTiO₃ particles with macropores of porous hydrous titania. These porous SrTiO₃ particles have a specific surface area of ~115 m²/g, which is one of the largest among micron-sized SrTiO₃ particles, thereby making them suitable for use as catalysts or photocatalysts.     

Fabrication of in situ elongated β-Sialon grains bonded to tungsten carbide via two-step spark plasma sintering

In order to reduce the difficulty of preparing binder-less cemented carbide and further broaden its application prospects, tungsten carbide toughened by in situ elongated β-Sialon grains was developed via sintering ball-milled WC and α-Si₃N₄ powders using Al₂O₃–ZrO₂ as a sintering aid and transformation additive. The two-step spark plasma sintering of the mixture at 1650 °C with dwelling at 1500 °C for 10 min was conducted under 30 MPa uniaxial pressure, and the densification behaviors, phase transformations, mechanical properties, and microstructures of the produced composites were investigated. The addition of Al₂O₃–ZrO₂ reduced the initial temperature of the densification process by approximately 100 °C and its final temperature by 200 °C (compared with the densification temperatures of pure WC and Si₃N₄ materials) and fully transformed α-Si₃N₄ to Sialon (Si–Al–O–N) phases. Microstructural characterization data showed that the WC matrix contained homogeneously distributed equiaxed and elongated β-Si₅AlON₇ grains. The WC composites containing in situ elongated β-Sialon grains exhibited an optimal hardness of 18.93 ± 0.03 GPa and enhanced fracture toughness of 10.43 ± 0.27 MPa m^1/2. The toughening mechanism of the β-Sialon phase involved the pull-out of elongated grains and crack bridging.     

Non-isothermal nitridation kinetics of Ti6Al4V in Al2O3-based refractories

To establish a kinetic model of nitridation of Ti6Al4V in Al₂O₃-based refractories, the non-isothermal nitridation of Ti6Al4V–Al₂O₃ composite refractories at various heating rates was investigated using a thermogravimetric (TG) analyzer for large samples. The activation energy (E) and kinetic model (G(α)) for the nitridation of Ti6Al4V were determined using the isoconversional and master plots methods, respectively. The nucleation and growth of nitriding products of the TiN solid solution was the controlling step in the nitridation of Ti6Al4V in Al₂O₃-based refractories. The Avrami-Erofeev kinetic model, depicted by the G(α) = [-ln (1-α)]⁴ equation, is the most rational kinetic model. The values of E and A for the nitridation of Ti6Al4V were calculated to be 214.99 kJ/mol and 1.46 × 10⁷ (S^?1), respectively.     

Highly compressible ceramic/polymer aerogel-based piezoelectric nanogenerators with enhanced mechanical energy harvesting property

Ceramic piezoelectric materials have orders of magnitude higher piezoelectric coefficients compared to polymers. However, their brittleness precludes imposition of large strains in mechanical energy harvesting applications. We report here that ice templating affords low bulk modulus lead-free aerogel piezoelectric nanogenerators (PENG) with unprecedented combination of flexibility and high piezoelectric response (voltage and power density). A modified ice templating protocol was used to fabricate piezoelectric nanocomposites of surface modified BaTiO₃ (BTO) nanoparticles in crosslinked polyethylene imine. This protocol allowed incorporating a significantly high fraction of BTO particles (up to 83 wt %) in the aerogel, while retaining remarkably high compressibility and elastic recovery up to 80% strain. The output voltage, at an applied compressive force of 20 N (100 kPa), increased with BTO loading and a maximum output voltage of 11.6 V and power density of 7.22 μW/cm² (49.79 μW/cm³) was obtained for PENG aerogels containing 83 wt% BTO, which is orders of magnitude higher than previously reported values for foam-based piezoelectric energy harvesters. The BTO/PEI PENGs also showed cyclic stability over 900 cycles of deformation. PENGs with higher porosity showed better elastic recovery and piezoelectric properties than lower porosity and higher BTO content aerogels. To the best of our knowledge, this is the first report to demonstrate the piezoelectric properties of high ceramic content aerogels having very high compressibility and elastic recovery.     

Al2O3 coated glass by aerosol deposition with excellent mechanical properties for mobile electronic displays

Al₂O₃ thin film was deposited on Gorilla glass using an aerosol deposition method to improve the mechanical property of cover glass for mobile electronic device. The deposited Al₂O₃ film (approximately 1 μm thick) was a polycrystalline structure and showed a high light transmittance of approximately 90% in the visible light region. The CIE color space (L*a*b) measurement also showed a characteristic corresponding to the acceptable optical range of the cover glass. Further, it was confirmed that the bending strength improved by 10 %, as compared with bare Gorilla glass (from 6970 kgf/cm² to 7704 kgf/cm²), and the Vickers hardness increased to approximately 1700–2000 HV, as compared with that of Gorilla glass (<700 HV). Owing to the improved mechanical properties, the Al₂O₃ thin film exhibited good anti-scratch properties and is expected to be applied to the cover glass of various display products.     

Efficient nitric oxide sensing on nanostructured La2MMnO6 (M: Co,Cu, Zn) electrodes

Selective detection of nitric oxide (NO) is a challenge for automotive exhaust monitoring systems due to the instability of sensing architectures operating under extreme environments. Herein, yttria-stabilized zirconia (YSZ) solid-electrolyte-based electrochemical gas sensor was developed using double perovskite electrodes (DPO) for selective detection of NO. The La₂MMnO₆ (M: Co, Cu, Zn) phases were synthesized by sol-gel processing of constituent salts and characterized for physicochemical and sensing properties to investigate the impact of transition metal cations present in octahedral environments on charge transport properties. The La₂ZnMnO₆ with a predominant Zn²⁺–Mn⁴⁺ charge ordering excelled in the sensing characteristics with high sensitivity (33 mV/decade for 3–80 ppm NO concentration), fast response/recovery time (52/42 s) and significant NO selectivity at 500 °C. The sensing behavior of double perovskites was comprehensively explored and found to abide by the mixed-potential model. Moreover, stable sensing properties over a period of three weeks indicate the here-described sensors to be potentially competitive for onboard exhaust monitoring in automobiles.     

A comprehensive exploration on the development of nano Y2O3 dispersed in AA 7017 by mechanical alloying and hot-pressing technique

The main objective of the present study is to develop AA 7017 alloy matrix reinforced with yttrium oxide (Y₂O₃, rare earth element) nanocomposites by mechanical alloying (MA) and hot pressing (HP) techniques for armor applications. AA 7017+10 vol % Y₂O₃ nanocomposites were synthesized in a high-energy ball mill with different milling times (0, 5, 10, and 20 h) to explore the structural refinement effect. The phase analysis and homogeneous dispersion of Y₂O₃ in AA 7017 nanocrystallite matrix were investigated by X-ray diffraction (XRD), various electron microscopes (HRSEM, and HRTEM), Particle Size Analyzer (PSA), and Differential Thermal Analysis (DTA). The nanostructured powders were hot-pressed at 500 MPa pressure with a temperature of 673k for 1hr. The consolidated sample results revealed significant grain refinement and the enhanced mechanical properties with the function of milling time in which the 20h sample exhibited improvement in the hardness (142 VHN - 260 VHN) and ultimate compressive strength (514 MPa–906.45 MPa) due to effective dispersion of Y₂O₃. The various strengthening mechanisms namely, grain boundary (27.02–32.69 MPa), solid solution (57.21 MPa), precipitate (189.79–374.62 MPa), Orowan (135.68–206.92 MPa), and dislocation strengthening (84.99–149.82 MPa) were determined and correlated to the total strength.     

In-situ growth flower-like binder-free 3D CuO/Cu2O-CTAB with tunable interlayer spacing for high performance lithium storage

Copper-based oxides are attractive anode materials for lithium-ion batteries (LIBs) due to their abundant resources, low cost, non-toxic and high capacity. However, copper-based oxides will produce a huge volume change during lithiation/delithiation, and the structural strain caused by periodic volume changes may cause the exfoliation of active materials. Herein, a flower-like binder-free three-dimensional (3D) CuO/Cu₂O-CTAB was prepared by introducing CTAB, which homogeneously grew in situ on a copper mesh framework. The binder-free 3D sample guarantees direct contact between the active material and the copper mesh, maintaining the structure stability. The flower-like CuO/Cu₂O-CTAB with a small size reveals larger active interfaces and provides more active sites. The introduction of CTAB enlarges the interlayer spacing of CuO/Cu₂O, increases the active sites for lithium storage, and adapts to the volume change of the material during lithiation/delithiation. In addition, the expanded interlayer structure helps decrease the ion diffusion energy barrier for accelerating electrochemical reaction kinetics. Therefore, CuO/Cu₂O-CTAB exhibits better lithium storage performance (2.9 mAh cm^?2 at 0.5 mA cm^?2) than bare CuO/Cu₂O (1.8 mAh cm^?2 at 0.5 mA cm^?2).     

Tuning the electronic and thermal transport behaviors of metal-dispersed Ti2O3 composites derived by metal–insulator transition

Thermal management requires an understanding of the relations among the thermal energy transfer, electronic properties, and structures of thermoconductive materials. Here, we enhanced the metal–insulator transition (MIT)-induced effect on the thermal conductivities of microstructure-controlled Ti₂O₃ composites containing W as a thermal conductive filler at approximately 450 K. To change the electronic and thermal transport properties, we varied the particle radii of the conductive phases in the raw material. The change in the calculated electronic thermal conductivity relative to the electrical conductivity of the W_x(Ti₂O₃)_1?x composite was enhanced by compounding the material. When x was reduced from 50 vol% to 20 vol% and the W particle diameter was reduced from 150 μm to 5 μm, the variation in the estimated electronic thermal conductivity of the W_x(Ti₂O₃)_1?x composite was increased by a factor of 2.01. The total thermal conductivity was also changed by the MIT. At x = 50 vol% and a W particle diameter of 5 μm, the maximum thermal conductivity change was 6.34 times larger than that of pure Ti₂O₃. The detailed relation between the MIT-induced changes in thermal transport and the microstructure were elucidated in classical effective medium approximations.     

Fabrication of Al2O3/AlN composite ceramics with enhanced performance via a heterogeneous precipitation coating process

To improve the thermal and mechanical properties of Al₂O₃/AlN composite ceramics, a novel heterogeneous precipitation coating (HPC) approach was introduced into the fabrication of Al₂O₃/AlN ceramics. For this approach, Al₂O₃ and AlN powders were coated with a layer of amorphous Y₂O₃, with the coated Al₂O₃ and AlN powders found to favor the formation of an interconnected YAG second phase along the grain boundaries. The interconnected YAG phase was designed to act as a diffusion barrier layer to minimize the detrimental interdiffusion between Al₂O₃ and AlN particles. Compared with samples prepared by a conventional ball-milling method, the HPC Al₂O₃/AlN composites exhibited less AlON formation, a higher relative density, a smaller grain size and a more homogeneous microstructure. The thermal conductivity, bending strength, fracture toughness and Weibull modulus of the HPC Al₂O₃/AlN composite ceramics were found to reach 34.21 ± 0.34 W m⁻¹ K⁻¹, 475.61 ± 21.56 MPa, 5.53 ± 0.29 MPa m^1/2 and 25.61, respectively, which are much higher than those for the Al₂O₃ and Al₂O₃/AlN samples prepared by the conventional ball-milling method. These results suggest that HPC is a more effective technique for preparing Al₂O₃/AlN composites with enhanced thermal and mechanical properties, and is probably applicable to other composite material systems as well.     

Low-temperature synthesis of nanometric apatite from biogenic sources

Nanosized calcium deficient carbonated apatite was synthesized from three different natural resources, namely chicken eggshells (calcite), cuttlefish bones (aragonite) and mussel shells (aragonite/calcite). The calcium precursors were ball-milled in (NH₄)₂HPO₄ or H₃PO₄ – containing aqueous medium for different times and then dried at temperatures ranging from 20 °C to 150 °C. The formation of hydroxyapatite (HA) is shown to be strongly affected by such treatment, the amount of synthesized HA increasing with temperature. Aragonite from cuttlebones and the aragonitic fraction of mussels is found to be transformed more easily with respect to the calcite from eggshells. The reaction is also favored by an acidic milling media with respect to basic one. The feasibility of the synthesis process at nearly room temperature described in the present work has interesting potentialities in the retention of the organic portions of the original biological resource in the produced nanometric inorganic compound.     

Mechanical and dielectric properties of porous magnesium aluminate (MgAl2O4) spinel ceramics fabricated by direct foaming-gelcasting

Porous ceramic materials have been broadly applied in various fields due to their multifunctional properties. Optimization of their microstructural characteristics, such as pore morphology, total porosity, and pore size distribution, which determine various properties of the final products, is crucial to improve their performances and thus extend their applications. In this study, single-phase porous MgAl₂O₄ materials were fabricated by direct foaming–gelcasting. With an increase in the foam volume from 260 to 350 mL, the total porosity and pore size of the porous ceramic increased, and its microstructure varied from mostly closed cells to open cells containing interconnected large pores (40–155 μm) and small circular windows (10–40 μm) in the ceramic skeleton. The total porosity could be tailored from 84.91% to 76.08% by modulating the sintering temperature and foam volume and the corresponding compressive strengths were in the range of 2.8–15.0 MPa. The compressive strength exhibited a power-law relationship with the relative density with indices of approximately 3.409 and 3.439, respectively. Porous MgAl₂O₄ ceramics exhibited low dielectric constants in the range of 1.618–1.910 at room temperature, which are well matched with theoretical calculations on account of a modified Bruggeman model. The porous MgAl₂O₄ ceramics with good mechanical and dielectric properties controlled easily by various sintering temperatures and foam volumes are promising for practical applications.     

Fe3O4-intercalated reduced graphene oxide nanocomposites with enhanced microwave absorption properties

Fe₃O₄-intercalated reduced graphene oxide (Fe₃O₄-rGO) nanocomposites were synthesized by an in situ reduction process. The results of XRD and XPS analyses suggested the successful formation of a Fe₃O₄ crystal phase within the rGO sheets. The SEM and TEM images demonstrated that Fe₃O₄ was flaky and was inserted stably within the rGO layers to form a typical sandwich-like structure. The hysteresis loops revealed the superparamagnetic behavior of the Fe₃O₄-rGO nanocomposites at room temperature. The electromagnetic parameters revealed that Fe₃O₄-rGO nanocomposites exhibited multiple dielectric relaxation and magnetic resonance. The reflection loss revealed that the maximum loss was −49.53 dB at 6.32 GHz for a thickness of 3.4 mm while the highest effective absorption bandwidth was 2.96 GHz.     

Influence of the cold sintering process and post annealing on the microstructure and Li-ion conductivity of LiTa2PO8 solid electrolyte

Recently, LiTa₂PO₈ (LTPO) has attracted interest as a potential Li-ion solid electrolyte material because of its high bulk ionic conductivity and low grain boundary ionic conductivity. However, most ceramic-based solid electrolytes are fabricated via the high-temperature sintering process (typically above 1000 °C); such temperatures can cause the evaporation of Li from the compound. To replace high-temperature sintering of ceramics, the cold sintering process (CSP) was introduced; this process enables the densification of ceramics and composites at extremely low temperatures (below 300 °C). In this work, we investigate the effect of using the CSP and post annealing on the microstructure and Li-ion conductivity of LTPO pellets. It is found that the CSP pellets have an amorphous phase between particles. This intermediate amorphous phase creates a better contact between particles and is hypothesized to lead to more Li-ion migration paths. The CSP pellet is found to have a high density and high ionic conductivity of (1.19 × 10^?5 S/cm). The pellet obtained via the CSP has Li-ion conductivity similar to that of the pellet obtained via dry pressing after it has been annealed. The CSP pellet after post annealing shows good connections between particles and a high Li-ion conductivity of 1.05 × 10^?4 S/cm, which is comparable to the conductivity of a pellet obtained via high-temperature sintering. This work provides new evidence that the CSP is a promising alternative to high-temperature sintering for fabricating ceramic solid electrolytes.