A Novel Top‐Seeded Infiltration Growth Technique for Fabricating Y–Ba–Cu–O Single‐Grain Superconductor Nano‐Composites

Top‐seed infiltration and growth technique (TSIG) is proposed to fabricate Y–Ba–Cu–O (YBCO) single‐grain superconductor nano‐composites, in which a solid source composition of nano‐Y₂O₃ + BaCuO₂ and a liquid source composition of Y₂O₃ + 10BaO + 16CuO are employed. As can be seen, this novel technique uses just one source of precursor powder of BaCuO₂, so it is more simplified and efficient. Microstructural observation indicates that fine Y₂BaCuO₅ (Y‐211) inclusions with a size from dozens of nanometers to about one hundred nanometers are successfully introduced in YBa₂Cu₃O_7?x (Y‐123) superconducting matrix, which can act as more effective pinning centers for improving the bulk performance. Superconducting property measurement shows that, a maximum trapped field of 0.36044 T is present at the center of the sample after magnetization by a permanent magnet (B = 0.5 T). These results prove that our proposed TSIG technique is a practical method for fabricating YBCO bulk superconductor nano‐composites with high performance.     

A Coated Infiltration Growth Technique for Fabricating Single‐Grain Y–Ba–Cu–O Bulk Superconductor

A coated infiltration growth technique was proposed to fabricate single‐grain Y?Ba?Cu?O bulk superconductor, in which a liquid source coated Y₂BaCuO₅ (Y‐211) preform was employed and the liquid source composition was 3BaO + 5CuO. Experimental results indicated that, the sample exhibited a single‐grain morphology on the top surface, and the liquid source coating always existed surrounding the bulk which contributed to the complete growth of the sample. The homogeneous distribution of fine Y‐211 inclusions in microstructure and a satisfactory J_c performance of 5.67 × 10⁴ A/cm² in self‐field at 77 K have also been observed.     

Synthesis and Microwave Dielectric Properties of Cu‐Doped ZnAl2O4

Spinel materials of composition Zn_1?xCu_xAl₂O₄ (ZCA, x = 0–0.015) were prepared via the conventional solid‐state route. The lattice structure, microstructure, and microwave dielectric properties were investigated as a function of Cu content. Cu doping was found to improve the sinterability and, meanwhile, significantly increase the quality factor (Q × f₀), which is due to the Cu‐O bond is stronger than Zn‐O bond, and inhibit the oxygen vacancy considered to be responsible for the enhanced Q × f₀ value of ZCA materials. The best microwave dielectric properties were obtained in Zn_0.99Cu_0.01Al₂O₄ with ε_r = 8.69, Q × f₀ = 69,300 GHz and τ_f = ?58.3 ppm/°C, which was sintered at 1520°C for 3 h in air.     

Enhanced Thermoelectric Properties in Cu‐Doped c‐Axis‐Oriented Ca3Co4O9+δ Thin Films

Highly c‐axis‐oriented Ca₃Co_4?xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.     

Resonance Magnetoelectric Effect in NaNbO3–NiFe2O4 Composite

Electric field‐induced magnetization characteristics are demonstrated in (100?x)NaNbO₃ – xNiFe₂O₄(x = 15, 25, 35, 45), synthesized by the solid‐state sintering method. The composites show well‐defined ferroelectric behaviors and magnetic characteristics. The CME effect characteristics with driving frequency in a range 10 k – 15 kHz were investigated at room temperature. The CME couplings increase initially with increasing the driving frequencies and then decrease with the further increase in the frequency. Large CME coefficients are obtained at electromechanical resonance frequency of 12.8 kHz. These lead‐free multiferroic composites exhibiting electrostatically induced ME resonance provide great opportunities for electric field‐tunable microwave devices.     

Phase Evolution of SiO2–Al2O3–ZnO–CaO–ZrO2–TiO2‐Based Glass with Added Y‐PSZ Particles

Yttria partially stabilized zirconia Y‐PSZ/glass‐ceramic composites were prepared by reaction sintering using powder mixtures of a SiO₂–Al₂O₃–ZnO–CaO–ZrO₂–TiO₂‐based glass and yttria partially stabilized zirconia (Y‐PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass‐ceramic matrix for high‐temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass‐ceramic material with dispersed zircon particles was prepared in situ. Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid‐like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass‐ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y‐PSZ/glass‐ceramic composites.     

A self‐repairing cermet anode: Preparation and corrosion behavior of (Cu–Ni–Fe)/NiFe2O4 cermet with synergistic action

In this paper, the cermet (Cu–Ni–Fe)/(NiFe₂O₄–10NiO) anodes were prepared through the powder metallurgy method, followed by being evaluated in the bench scale (200 A) electrolysis tests for more than 1000 hour. The results showed that the as‐prepared anodes exhibited excellent corrosion resistance with corrosion rate less than 0.99 cm/a, which satisfied the requirements of the aluminum industry. The analysis results were confirmed by SEM, EDS, and XRD. The results showed that the outstanding corrosion resistance of the anodes relied on a continuous and dense NiFe₂O₄ film formed on the surface of the anode material, which protected the inner structure of anode material during electrolysis. Finally, a model based on the synergistic action between the metal phase and the ceramic phase was built to illustrate the forming mechanism of the NiFe₂O₄ passivating film.     

Role of Nano‐ and Micron‐Sized Particles of TiO2 Additive on Microwave Dielectric Properties of Li2ZnTi3O8 – 4 wt% TiO2 Ceramics

Microwave dielectric ceramics with the composition of Li₂ZnTi₃O₈ – 4 wt% TiO₂ were synthesized by the conventional solid‐state reaction. 4 wt% TiO₂ powders with different particles size were added to the Li₂ZnTi₃O₈ ceramic. Then the ceramic samples were sintered at temperatures 1075°C, 1050°C, 1000°C, and 950°C for 4 h. The effect of the particles size of TiO₂ additive on the microwave dielectric properties of the ceramics has been investigated. In the study two categories of particles size of TiO₂ additive have been used; (i) Nanoparticle (50 nm), (ii) Micron sized (40, 5, 1 μm) powder. X‐ray showed that the TiO₂ additive has not solved in the LZT structure and has not almost undergone chemical reaction with the LZT ceramic. The results showed that the addition of TiO₂ nanoparticles to the LZT ceramics significantly improved the density and a dense and uniform microstructure and also abnormal grain growth were observed by SEM. The use of TiO₂ nanoparticle reduces porosity and leads to an increase in green density. The maximum density was found to be 98.5% of the theoretical density and the best relative permittivity of 28, quality factor of 68000 GHz and τ_f value of ?2 ppm/°C were obtained for the samples added with 4 wt% of the TiO₂ nanoparticles, sintered at 1050°C for 4 h.     

Synthesis of Single‐Phase β‐Yb2Si2O7 and Properties of Its Sintered Bulk

Single‐phase β‐Yb₂Si₂O₇ was synthesized by solid‐state reaction using Yb₂O₃ and SiO₂ gel. SiO₂ gel significantly decreased the synthesis temperature and shortened the holding time. Bulk Yb₂Si₂O₇ was obtained by pressureless sintering. Grain size, relative density (92.9%), and flexural strength [(182.3 ± 2.0) MPa] were enhanced as the sintering temperature increased and equiaxed grains were obtained with an average grain size of approximately 3 μm. Bulk Yb₂Si₂O₇ possessed a suitable thermal expansion coefficient [(4.64 ± 0.01) × 10^?6/K] between 473 and 1573 K, and the thermal conductivities at 300 and 1400 K were 4.31 and 2.27 W/m·K, respectively.     

Rapid Synthesis of Mesoporous,Nano‐Sized MgCr2O4 and Its Catalytic Properties

Monophasic MgCr₂O₄ has been synthesized by calcining the gel formed by the addition of epoxide to an ethanolic solution containing MgCl₂·6H₂O and CrCl₃·6H₂O. The sample has been characterized by a variety of analytical techniques including powder X‐ray diffraction (PXRD), FT‐IR, Raman, UV–Visible spectroscopy, transmission electron microscopy, and magnetic measurements at room temperature. Calcining the xerogel at 500°C and 700°C for 2 h yielded MgCr₂O₄ (yield of almost 61% by weight). BET surface area of 33.95 m²/g with an average pore diameter of 28.45 nm was obtained for the sample after calcination at 700°C. Square facets of the cubic spinel structure were observed in TEM images with an average crystallite diameter of 18 nm. HR‐TEM experiments and SAED measurements confirmed the spinel structure and negated the presence of other phases. The presence of MO₄ tetrahedral and MO₆ octahedral units in MgCr₂O₄ has also been evidenced from FTIR and Raman spectra. The sample showed paramagnetic behavior at room temperature with μ_eff of 3.54 B.M suggesting the presence of Cr in III oxidation state. Its use as an efficient catalyst for the oxidative degradation of Xylenol Orange (XO) and the photo degradation of Rhodamine‐6G (Rh‐6G) dyes have been demonstrated as these dye molecules are environmental pollutants.     

Effect of ZrO2 Addition on Densification and Mechanical Properties of MgAl2O4–CaAl4O7–CaAl12O19 Composite

Although the platelet structure of calcium hexaluminate (CaAl₁₂O₁₉, or CA₆) grains can strengthen and toughen the Al₂O₃–MgO–CaO system materials designed in the high‐alumina region, it also results in poor densification and subsequent accelerated slag penetration for refractory application. Considering this aspect, MgAl₂O₄–CaAl₄O₇–CaAl₁₂O₁₉ composite was fabricated by solid‐state reaction sintering in this work, and the effect of ZrO₂ addition on densification and mechanical properties was investigated. The results showed that the CA₆ grains presented a more equiaxed morphology by addition of ZrO₂, contributing to form highly dense microstructures after heating at 1600°C without evident grain coarsening. The compressive strength and flexural strength were greatly enhanced mainly due to the significant decrease in porosity and pore sizes. Besides, the increased content of ZrO₂ plays an active role in toughening this composite attributed to the dense microstructure and strong bonding with higher strength, as well as considerable t‐ZrO₂ transformability.     

A Reliable Method for Recycling (RE)‐Ba‐Cu‐O (RE: Sm,Gd, Y) Bulk Superconductors

Single grain (RE)‐Ba‐Cu‐O (RE: Sm, Gd, Y) high‐temperature superconductors are able to generate high magnetic fields. However, the relatively high cost of the raw materials and the low yield of the manufacturing process have impeded the development of practical applications of these materials to date. This article describes a simple, reliable, and economical method of recycling failed bulk (RE)‐Ba‐Cu‐O (RE: Sm, Gd, Y) samples. Sixty‐four failed bulk samples, with diameters up to 31 mm, were recycled with a yield of 90%. The key innovation in this recycling process involves reintroducing the liquid phase into the melt process, which is normally lost during the primary peritectic processing of these materials. This enables the direct re‐growth of failed samples from solid form without the need for re‐grinding into powder. We also demonstrate that the superconducting performance and microstructure of the recycled samples is similar to that of the primary grown samples.     

Processing and Properties of Eu3+‐Doped Barium Bismuth Titanate (BaBi4Ti4O15) Glass–Ceramic Nanocomposites

Precursor glasses for the ferroelectric barium bismuth titanate (BaBi₄Ti₄O₁₅) (BBiT) have been prepared by the melt‐quench technique in the SiO₂–K₂O–BaO–Bi₂O₃–TiO₂ (SKBBT) glass system with and without Eu₂O₃ doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X‐ray diffraction (XRD), electron microscopy (FE‐SEM, TEM), and FT‐IR reflectance spectroscopy. FE‐SEM images show the formation of randomly oriented hexagonal rod‐shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT‐IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm^?1. The activation energy of crystallization (E_c) varies from 295 to 307 kJ/mol. The dielectric constants (ε_r) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat‐treated GCs show higher ε_r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the ⁵D₀ → ⁷F₂ transition. An intense 466 nm excitation band corresponding to the ⁷F₀ → ⁵D₂ transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat‐treatment times led to a 15‐fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu³⁺ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam^0.5) values obtained in the GCs are high and suitable for structural applications.     

Nano‐Hydroxyapatite Improves the Properties of β‐tricalcium Phosphate Bone Scaffolds

β‐Tricalcium phosphates have been widely used as biomaterials for bone substitutes; however, the poor mechanical properties limit the application in bearing loading bones. In this study, nano‐hydroxyapatite has been introduced to improve the mechanical properties for porous bioceramic scaffolds. Nanocomposites containing 0–10 wt% needle‐like nano‐hydroxyapatite were prepared for investigation. It has been found that needle‐like nano‐hydroxyapatite improves the toughness, hardness, and compressive strength of the porous β‐tricalcium phosphates scaffolds, as well as the microstructure properties. The study provides a reference for the development of safe, excellent bone scaffolds for bone tissue engineering.     

Surface Analysis of Cr2O3‐, CoO‐, and Al2O3‐Doped Iron–Phosphate Glasses at High Temperature

Surface structures of iron–phosphate glasses were examined using X‐ray photoelectron spectroscopy (XPS). Cr₂O₃, CoO, and Al₂O₃ were introduced to the glass by the replacement of a part of Fe₂O₃, and the simulated fission products are also added. The obtained glasses showed high chemical durabilities by MCC‐1 test. In situ high‐temperature and room‐temperature XPS measurements were conducted on the polished sample surfaces and also those after 1‐week chemical durability test. Unique trends were observed in XPS spectra on heating and after the chemical durability test, respectively. Nature of the glass surface of iron–phosphate glasses was explained from the point of view of surface energy, and the origin of high chemical durability and the effect of chromium ions were discussed based on the changes on surface composition and valence states of transition‐metal ions.     

Solid Solution Effects on the Thermal Properties in the MgAl2O4–MgGa2O4 System

Solid solution effects on thermal conductivity within the MgO–Al₂O₃–Ga₂O₃ system were studied. Samples with systematically varied additions of MgGa₂O₄–MgAl₂O₄ were prepared and the laser flash technique was used to determine thermal diffusivity at temperatures between 200°C and 1300°C. Heat capacity as a function of temperature from room temperature to 800°C was also determined using differential scanning calorimetry (DSC). Solid solution in the MgAl₂O₄–MgGa₂O₄ system decreases the thermal conductivity up to 1000°C. At 200°C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. At 1000°C, the thermal conductivity decreased 13% with a 5 mol% addition. Steady‐state calculations showed a 12.5% decrease in heat flux with 5 mol% MgGa₂O₄ considered across a 12 inch thickness.     

Extremely Enhanced Nonlinear Current–Voltage Properties of Tb‐Doped CaCu3Ti4O12 Ceramics

Nonlinear current–voltage properties of CaCu₃Ti₄O₁₂ ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu₃Ti₄O₁₂ resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of ~29.67 and breakdown electric field strength of ~1.52 × 10⁴ V/cm were obtained in the Ca_0.775Tb_0.15Cu₃Ti₄O₁₂ ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.     

The effect of SiO2 on electrical properties of low‐temperature‐sintered ZnO–Bi2O3–TiO2–Co2O3–MnO2‐based ceramics

ZnO–Bi₂O₃–TiO₂–Co₂O₃–MnO₂‐based (ZBTCM) varistors were fabricated via the conventional solid‐state method, and the effect of SiO₂ content on the phase transformation, microstructure, and electrical properties of the ZBTCM had been investigated. Results showed that this varistor can be sintered at a low temperature of 880°C with a high sintering density above 0.95 of the ZnO theoretical density. In these components, SiO₂ acts as a controller in ZnO grain growth, decreasing the grain size of ZnO from 3.67 to 1.92 μm, which in turn results in an increase in breakdown voltage E_1mA from 358.11 to 1080 V/mm. On the other hand, SiO₂ has a significant influence on the defect structure and component distribution at grain‐boundary regions. When SiO₂ content increases from 0 to 4 wt%, the value of the interface state density (N_s) increases sharply. At the same time, the electrical properties are improved gradually, and reach an optimized value with the nonlinear coefficient (α) up to 54.18, the barrier height (?_b) up to 2.90 eV, and the leakage current (I_L) down to 0.193 μA/cm².