Optical properties of γ-Fe2O3 nanoparticles dispersed on sol–gel silica spheres

Two types of γ-Fe₂O₃ nanoparticles, pure γ-Fe₂O₃ and γ-Fe₂O₃ dispersed on sol–gel silica spheres (γ-Fe₂O₃/SiO₂) in thin film form were prepared by the sol–gel technique. Transmission electron microscopy, X-ray diffraction, optical transmittance and FTIR studies along with photoluminescence measurements were carried out for characterizing the samples. The X-ray diffraction patterns of both γ-Fe₂O₃ nanoparticles and γ-Fe₂O₃/SiO₂ indicated their phase-pure forms which were supported by the FTIR spectra. The average sizes of the nanoparticles obtained from transmission electron microscopy studies were 4 nm for both types of samples. Optical transmittance studies indicated direct allowed transitions with two band gaps at 2.43 and 3.07 eV. Although both types of samples showed excitonic luminescence at 2.38 eV (at room temperature), the luminescence intensity of the γ-Fe₂O₃/SiO₂ was higher than that of pure γ-Fe₂O₃.     

Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

Self-assembly of β-Ga2O3 nanobelts

Self-assembly of β-Ga₂O₃ (beta-gallium oxide) nanobelts with diameters of 50–100 nm and lengths of tens to hundreds of microns have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Under appropriate conditions such as nanobelts concentration, controlled solvent evaporation, β-Ga₂O₃ nanobelts assemble into a fan-like structure on the substrate. A tendency of these nanobelts to align parallel to each other was also observed. The mechanism behind the formation of self-assembly of β-Ga₂O₃ nanobelts has been proposed on the basis of lateral capillary forces.     

Two-fold interferometric measurements of piezo-optic constants: application to β-BaB2O4 crystals

We present the interferometric technique which allows to measure piezooptical and photoelastic characteristics of crystal materials of any symmetry. The offered two-fold interferometric method enables to determine all independent non-zero piezooptic and photoelastic constants by measuring pressure induced changes of optical path. As advantage to known acoustooptical techniques this method allows to measure both the absolute magnitude and sign of photoelastic constants. In general case the determination of 36 components of piezooptic tensor needs to carry out 57 measurements on 16 samples. The corresponding relationships are derived. As an example we apply here the interferometric technique to measure the piezooptic and photoelastic constants in trigonal β-BaB₂O₄ crystals.     

Fabrication of chain-like Mn2O3 nanostructures via thermal decomposition of manganese phthalate coordination polymers

A novel manganese coordination polymer [Mn(Pht)(H₂O)]_n as a precursor was obtained by chemical precipitation involving an aqueous solution of anhydrous manganese acetate and phthalate anion as a potential O-banded ligand. Fourier transform infrared (FT-IR) results proved that phthalate anions coordinate to metal cations as a chelating bidentate ligand, making polymeric structure. The Mn₂O₃ nanostructures have been prepared via thermal decomposition of as-prepared manganese phthalate polymers as precursor in the presence of oleic acid (OA) and triphenylphosphine (TPP) as a stabilizer and capping. Different approaches such as FT-IR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the products. TEM images and XRD analysis indicated that the as-synthesized chain-like Mn₂O₃ has a crystal phase of cubic syngony with a mean size of ∼40 nm.     

Growth of β-Ga2O3 nanorods by ammoniating Ga2O3/V thin films on Si substrate

This paper reports that/3-Ga2O3 nanorods have been synthesized by ammoniating Ga2O3 films on a V middle layer deposited on Si（111） substrates. The synthesized nanorods were confirmed as monoclinic Ga2O3 by x-ray diffraction,Fourier transform infrared spectra. Scanning electron microscopy and transmission electron microscopy reveal that the grown β-Ga2O3 nanorods have a smooth and clean surface with diameters ranging from 100 nm to 200 nm and lengths typically up to 2μm. High resolution TEM and selected-area electron diffraction shows that the nanorods are pure monoclinic Ga2O3 single crystal. The photoluminescence spectrum indicates that the Ga2O3 nanorods have a good emission property. The growth mechanism is discussed briefly.     

Polyacrylonitrile electrolytes: 1. A novel high-conductivity composite polymer electrolyte based on PAN, LiClO4 and α-Al2O3

In this work, a series of novel solid-type α-Al₂O₃-containing polyacrylonitrile (PAN)-based composite polymer electrolytes (CPE) with high conductivity and high mechanical property at room temperature has been prepared. The effect of the addition of α-Al₂O₃ on the properties of the PAN-based composite polymer electrolyte has been analyzed. The best conductivities obtained at room temperature is 5.7×10⁻⁴ S cm⁻¹ from the CPE with 7.5 wt.% α-Al₂O₃ and 0.6 LiClO₄ per PAN repeat unit. The stress–strain test result indicates that the membranes prepared possess high yield stress (73 kg cm⁻²) suitable for serving as separators in the solid-state lithium and lithium ion batteries and high yield elongation (225%) pliable to form good interface with electrodes. Also discussed are the effects of the addition of the ceramics on the interactions in the system and the possible conduction mechanism.     

Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method using α-Fe₂O₃ and γ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ₃ and τ₄ are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3 wt% to 40 wt%, the lifetime τ₃ keeps nearly unchanged, while the longest lifetime τ₄ shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ₄ is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.     

Ion-beam irradiation effect on solid-phase growth of β-FeSi2

Effects of Ar⁺ ion-beam irradiation on solid-phase growth of β-FeSi₂ have been investigated. Fe (10 nm)/Si structures were irradiated with 25 keV Ar⁺ (5.0×10¹⁵ cm⁻²) at a temperature of 25°C (sample A) or 400°C (sample B), and subsequently annealed at 800°C. A reference was obtained after annealing without irradiation (sample C). X-ray diffraction results indicated that β-FeSi₂ was formed after annealing at 800°C for 5 h, and the formation rate was the fastest for sample A and the slowest for sample C, i.e., A>BC. However, Auger electron spectroscopy measurements showed that atomic mixing at Fe/Si interface before annealing was B>AC. These results suggested that amorphization of Si substrate, in addition to atomic mixing, enhanced the solid-phase growth of β-FeSi₂, which was confirmed experimentally. Moreover, a direct band gap of 0.89 eV was observed for the sample with pre-amorphization by the Fourier-transform infrared (FT-IR) spectroscopy measurements. These enhancement effects were attributed to that the phase transition to β-FeSi₂ was accelerated by atomic arrangement induced during annihilation of excess vacancies. These enhancement effects can be utilized for nano-fabrication of β-FeSi₂ by using focused ion-beam irradiation.     

Electrical and mechanical properties of proton conducting SrCe0.95Yb0.05O3 − α

Yb³⁺-doped ceramic strontium cerate of exactly the composition SrCe_0.95Yb_0.05O_{3 − α} was prepared, having a relative density of 99.0 (± 0.3%). Great care was taken to obtain homogeneous, carbonate free material. Analysis are made of the X-ray powder diffraction pattern of the as-prepared dense ceramic, resulting in the orthorhombic unit cell parameters a = 6.997(2) Å, b = 12.296(3) Å, c = 8.588(2) Å, Z = 8 and d_x = 5.806(2) g cm⁻³. Bending strength values of the ceramic in non-proton and proton conducting state are found to be 177 and 194 MPa respectively. The ceramic kept under proton conducting conditions for 500 h at 300 °C to 800 °C in a N₂ flow containing 155 mbar water vapour and 245 mbar H₂, have shown to remain chemically and structurally stable. Impedance spectroscopy measurements of the bulk conductivity of the proton conducting ceramic revealed an activation energy of 53.2 kJ mol⁻¹ and a preexponential factor of 359.1 (Ω cm)⁻¹ K. In the non-proton conducting state the ceramic is mainly oxygen ion vacancy conducting, which indicates that charge compensation on substituting Yb⁺³ in SrCeO₃ takes place by oxygen ion vacancies.     

Subsolidus phase relation in the Bi_2O_3–Fe_2O_3–La_2O_3 system

Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light.In this paper,we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi2O3–Fe2O3–La2O3system.The X-ray diffraction data shows that in this ternary system the ternary compound does not exist,while seven binary compounds(including one solid solution series Bi1 xLaxO1.5with 0.167≤x≤0.339)are obtained and eight compatibility triangles are determined.     

Growth and properties of air-processed GdBa2Cu3O7−δ superconductors with fined Gd2BaCuO5 and Gd2Ba4CuFeOy additions

We have succeeded in synthesizing a powder form of Gd₂Ba₄CuFeO_y (Gd2411) in air. GdBa₂Cu₃O_7−δ (Gd123)/Gd₂BaCuO₅ (Gd211) precursor powders added with different amounts of Gd₂Ba₄CuFeO_y (x = 0, 0.002, 0.004, 0.02) in molar ratio to Gd123 have been fabricated successfully into the form of large, single grains by the top seeded melt growth (TSMG) process. The relation between the additions amounts of Gd2411/Gd211 and critical current density (J_C) was analyzed. We found Gd2411 particles stably exist in the Gd123 matrix without degradation of superconducting properties owing to the existence of the Fe magnetic ion. The trapped field was observed to increase significantly compared with the bulk without Gd2411 additions.     

Effect of intervening structure between CuO2 sheets in heavily Fe-substituted high-Tc superconductor FeSr2YCu2O6+δ

Heavily Fe-substituted Ba₂YCu₃O_6+δ-type compound FeSr₂YCu₂O_6+δ exhibits superconductivity around 60 K, only when it is annealed in N₂ and subsequently in O₂. Cationic distribution in this compound is strongly dependent on ionic radius at the Y site, and its superconducting properties are affected by the cationic distribution. In contrast, although the compound with the substitution of fluorite-type unit for Y has cationic order, it does not exhibit superconductivity. We have analyzed the crystal structure of the compounds with the substitution of other lanthanoid elements for Y and with substitution of fluorite-type unit for Y.     

Effect of Ca doping on the superconducting properties of GdBaSrCu3O7−δ bulk samples

Gd_1−xCa_xBaSrCu₃O_7−δ samples (0  x  0.1) were prepared via solid-state reaction. Four-point probes method was used for resistance versus temperature measurements. Results show decrease in T_c by increasing x content. This variation is assumed to be irrelevant to the different phases or impurity effects since X-ray patterns show all samples are tetragonal single-phase. Ca doping decreases the oxygen content and lattice parameters of the samples. It is suggested that Ca prevents the dislocation of oxygen, and then disrupts the hole concentration of the system and antiferromagnetic correlation at CuO₂ planes. Subsequently, destroys the superconductivity of the samples.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Effects of RE2O3 (RE = Tm, Sc, Yb) addition on the superconducting properties of ErBa2Cu3Oy

We investigated the effects of added Tm₂O₃, Sc₂O₃, and Yb₂O₃ on the superconducting properties of sintered Er123 samples. Tm₂O₃ addition caused the least T_c degradation, exhibiting a T_c above 90 K even for 17 vol% addition. Samples with added Sc₂O₃ maintained a T_c at above 90 K up to an addition of 7.2 vol%, while Yb₂O₃-containing samples showed a monotonic decrease in T_c with increased vol% of added Yb₂O₃. Tm₂O₃-containing samples exhibited a slight increase in J_c(0.1 T)/J_c(0) and had constant J_c values even for 17 vol% addition. XRD and SEM results indicate that the Tm₂O₃ is very stable in the superconducting matrix.     

Influence of postdeposition annealing on structural properties and electrical characteristics of thin Tm2O3 and Tm2Ti2O7 dielectrics

We describe the structural properties and electrical characteristics of thin thulium oxide (Tm₂O₃) and thulium titanium oxide (Tm₂Ti₂O₇) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm₂Ti₂O₇ film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 10¹¹ eV⁻¹ cm⁻², and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm₂O₃ film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress.     

Effect of TiO2/Al2O3 film coated diamond abrasive particles by sol-gel technique

The diamond abrasive particles were coated with the TiO₂/Al₂O₃ film by the sol-gel technique. Compared with the uncoated diamonds, the TiO₂/Al₂O₃ film was excellent material for the protection of the diamonds. The results showed that the incipient oxidation temperature of the TiO₂/Al₂O₃ film coated diamonds in air atmosphere was 775 °C, which was higher 175 °C than that of the uncoated diamonds. And the coated diamonds also had better the diamond's single particle compressive strength and the impact toughness than that of uncoated diamonds after sintering at 750 °C. For the vitrified bond grinding wheels, replacing the uncoated diamonds with the TiO₂/Al₂O₃ film coated diamonds, the volume expansion of the grinding wheels decreased from 6.2% to 3.4%, the porosity decreased from 35.7% to 25.7%, the hardness increased from 61.2H_RC to 66.5H_RC and the grinding ratio of the vitrified bond grinding wheels to carbide alloy (YG8) increased from 11.5 to 19.1.