Highly selective ethanol In2O3-based gas sensor

The sensitive composite material was prepared by loading Pt and La₂O₃ into ultrafine In₂O₃ matric material (8 nm) synthesized by microemulsion method. A highly selective ethanol gas sensor was developed based on hot-wire type gas sensor, which was sintered in a bead (0.8 mm in diameter) to cover a platinum wire coil (0.4 mm in diameter). The gas sensor was operated by a bridge electric circuit. The influences of La₂O₃ and Pt additives on C₂H₅OH sensing properties of In₂O₃-based gas sensor were discussed. The addition of La₂O₃ resulted in a prominent selectivity for C₂H₅OH, and the addition of Pt improved the response rate to C₂H₅OH without affecting the sensitivity. The temperature and humidity characteristics of the sensor output were also investigated. The selective sensor had low power consumption, significantly minor humidity and temperature dependence, high selectivity and prominent long-term stability.     

Preparation of In2O3 octahedrons by heating InCl3 aqueous solution on the Si substrate

In₂O₃ octahedrons have been synthesized by heating InCl₃ aqueous solution on the Si substrate at 400-900 °C for 2 h. The average size of In₂O₃ octahedrons is decreased by increasing the heating temperature. The In₂O₃ octahedrons are single-crystalline with the body-centered cubic structure and have controllable sizes in the range of 0.7-1.0 μm. A possible mechanism was also proposed to account for the formation of In₂O₃ octahedrons. A strong photoluminescence with a peak at 458 nm was observed from the In₂O₃ octahedrons at room temperature. This emission can be attributed to oxygen vacancies and indium-oxygen vacancy centers.     

Controlled synthesis and photocatalytic properties of porous hollow In2O3 microcubes with different sizes

Uniform single-crystalline In(OH)₃ hollow microcubes have been synthesized in large quantities via a hydrothermal reaction of InCl₃ with NaF and ethylene glycol (EG) at 140–220 °C for 12 h. Porous In₂O₃ hollow microcubes with a polycrystalline cubic structure can be obtained via calcining In(OH)₃ precursors at 400 °C for 2 h in air. Controlled Synthesis of In(OH)₃ and In₂O₃ hollow microcubes with the average edge lengths in the range of 2.0–4.7 μm can be achieved by changing the hydrothermal reaction temperature. The In(OH)₃ hollow microcubes were formed via an EG-assisted oriented attachment growth route using HF bubbles as the templates. Photocatalytic activities of the as-synthesized porous In₂O₃ hollow microcubes were studied at room temperature. The results indicated that the hollow In₂O₃ nanostructures display high photocatalytic activity in the photodegradation of rhodamine B and methyl orange.     

Microstructure and mechanical properties of small amounts of In2O3 reinforced Pb(ZrxTi1−x)O3 ceramics

Piezoelectric Pb(Zr_xTi_1−x)O₃ (PZT) ceramics with small amount (0.5-2.0 wt.%) of In₂O₃ are prepared by conventional sintering method. Based on X-ray diffraction analysis, the tetragonality of PZT matrix decreases with In₂O₃ content, indicating that In₂O₃ diffuses into PZT matrix. The microstructure of PZT matrix is significantly refined by doping small amounts of In₂O₃. The grain size reduction and the matrix grain boundary reinforcement are the probable mechanism responsible for the high strength and hardness in the PZT/In₂O₃ materials. The enhancement in Young’s modulus is attributed to In³⁺ substitution. The decreased tetragonality with In₂O₃ addition results in less crack energy absorption by domain switching and, hence, causes the small reduction in fracture toughness.     

Low temperature preparation of nanocrystalline Sr0.5Ba0.5Nb2O6 powders using an aqueous organic gel route

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 °C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.     

Synthesis and electrochemical properties of LiV3O8 phase

Lithium vanadium oxide was synthesized by a new method in which LiOH, V₂O₅ and NH₄OH were used as the starting materials to synthesize a precursor containing Li and V, and then obtain the resulting product by calcining the precursor. The LiV₃O₈ compound prepared by this synthesis method gave a good charge-discharge and cycle performance. A specific capacity of 258 mAh/g is obtained in the range of 1.8−4.0 V in the first cycle and 247 mAh/g in the eighth cycle.     

Solvothermal synthesis of In(OH)3 nanorods and their conversion to In2O3

In this work, we demonstrate that monodisperse indium hydroxide (In(OH)₃) nanorods constructed with parallel wire-like subunits have been fabricated via a acrylamide-assisted synthesis route without any template. NH₃ from the hydrolysis of acrylamide acts as the OH⁻ provider. The structure and morphology of as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TG). A detailed mechanism has been proposed on the basis of time-dependent experimental results. Furthermore, by annealing In(OH)₃ precursors at 500 °C for 3 h in air, In₂O₃ samples were obtained with the designed morphology.     

Photocatalytic hydrogen production over Na2Ti2O4(OH)2 nanotube sensitized by CdS nanoparticles

Na₂Ti₂O₄(OH)₂ nanotubes were obtained by hydrothermal reaction of TiO₂ with concentrated NaOH solution. CdS nanoparticles were then decorated on Na₂Ti₂O₄(OH)₂ nanotubes through partial ion-exchange method. The composite photocatalysts were characterized by X-ray diffraction (XRD), ultraviolet-visible spectra (UV-vis), transmission electron microscope (TEM), etc. The results showed that CdS nanoparticles of 5-6 nm were anchored on the surface of the Na₂Ti₂O₄(OH)₂ nanotubes. Under irradiation of visible light (λ ≥ 430 nm), the prepared CdS/Na₂Ti₂O₄(OH)₂ showed high photoactivity for hydrogen production.     

(ZnO)3In2O3 fine powder prepared by combustion reaction of nitrates-glycine mixture

Conducting fine powder was obtained in the ZnInO system by combustion of the gel prepared from an aqueous solution of mixed zinc and indium nitrates in the presence of glycine. Glycine worked as a fuel as well as a gelling agent in the combustion under the strong oxidizing power of the nitrates. In spite of the low furnace temperature of 350 °C, the product was (ZnO)₃In₂O₃ which has been obtained above 1260 °C in a solid state reaction of a mixture of ZnO and In₂O₃. The combustion synthesis led to an aggregated fine powder of hexagonal platelets of about 40 nm in diameter. Its compacted mass showed an electrical resistivity of about 700 Ω cm. The agglomeration was improved by dispersing the fine powder in an acetic acid aqueous solution.     

Growth studies and characterization of In2S3 films prepared by hydrothermal method and their conversion to In2O3 films

For the first time, In₂S₃ films composed of nano-/microflakes were fabricated on fluorine-doped tin oxide (FTO) substrate using a simple and effective hydrothermal method. The structure, composition and morphology were examined by X-ray diffraction, energy-dispersive X-ray spectroscopy and field emission scanning electron microscopy. It was found that the reaction time, reaction temperature and the molar ratio of the reactants play key roles in controlling the final morphologies. The possible growth mechanism for the formation of In₂S₃ thin films was proposed. And the optical and photoelectrochemical properties were also investigated. In addition, In₂O₃ films were obtained by annealing the In₂S₃ precursor films in air at 500 °C.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Comparative investigation of structure and dielectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (65/35) and 10% PbZrO3-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (65/35) ceramics prepared by a modified precursor method

Relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) and 10% PbZrO₃-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramics were both prepared by a modified precursor method, which was based on the high-temperature synthesis of an oxide precursor that contained all the B-site cations for the consideration of B-site homogeneity. The dielectric properties of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramic was more of normal ferroelectric behavior, but the high dielectric constant (?_m = 34,200 at 1 kHz) and piezoelectric constant (d₃₃ = 709 pC/N) were observed for this composition close to the morphotropic phase boundary. Comparatively, introduction of 10% PbZrO₃ into Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (65/35) ceramics enhanced the diffuse phase transition as well as the rhombohedral to tetragonal phase transition temperature, while it also kept the high dielectric constant (?_m = 29,600 at 1 kHz) and piezoelectric constant (d₃₃ = 511 pC/N).     

Y2O3:Eu microstructures: Hydrothermal synthesis and photoluminescence properties

Hexagonal microprisms of yttrium hydroxide (Y(OH)₃) with tuned diameter and height have been successfully prepared for the first time via a facile hydrothermal process using sodium citrate as the shape modifying agent. Y(OH)₃ microspheres with diameter of ca. 2.5 μm and microtubes with an average length about 13 μm, outer diameter about 3 μm and tube thickness about 800 nm were also obtained in current reaction systems. The possible formation mechanism for the Y(OH)₃ microstructures was briefly proposed. Y₂O₃:Eu³⁺ (5%) microstructures with similar morphologies was obtained after thermal treatment of the as-prepared Y(OH)₃:Eu³⁺ microstructures at 700 °C for 4 h. Results show that the relative emission intensity of the Y₂O₃:Eu³⁺ microprisms is about 8 times as those of the Y₂O₃:Eu³⁺ microtubes and microspheres under excitation of 259 nm ultraviolet light. The products were characterized by XRD, SEM, and EDS.     

Preparation and characterization of Y3Al5O12 (YAG) nano-powder by co-precipitation method

YAG precursor was synthesized by a co-precipitation method from a mixed solution of aluminum and yttrium nitrates with aqueous ammonia as the precipitator. The structure, phase evolution and morphology of YAG precursor and the sintered powders were studied by means of IR, TG/DTA, XRD, TEM methods. It was found the precursor with approximate composition of Al(OH)₃·0.3[Y₂(OH)₅·(NO₃)₂·2H₂O] directly transformed to pure-YAG phase at 800 °C and no intermediate phases were detected. YAG nanocrystalline powders from sintering the precursor at different temperatures were less-aggregated and the diameters of the grains were about 40-100 nm. BET surface area of the particles decreased with increase of calcination temperature and the powder sintered at 800 °C can be used for fabrication of transparent YAG ceramics.     

Heterostructured Fe3O4/Bi2O2CO3 photocatalyst: Synthesis,characterization and application in recyclable photodegradation of organic dyes under visible light irradiation

Heterostructured Fe₃O₄/Bi₂O₂CO₃ photocatalyst was synthesized by a two-step method. First, Fe₃O₄ nanoparticles with the size of ca. 10 nm were synthesized by chemical method at room temperature and then heterostructured Fe₃O₄/Bi₂O₂CO₃ photocatalyst was synthesized by hydrothermal method at 180 °C for 24 h with the addition of 10 wt% Fe₃O₄ nanoparticles into the precursor suspension of Bi₂O₂CO₃. The pH value of synthesis suspension was adjusted to 4 and 6 with the addition of 2 M NaOH aqueous solution. By controlling the pH of synthesis suspension at 4 and 6, sphere- and flower-like Fe₃O₄/Bi₂O₂CO₃ photocatalysts were obtained, respectively. Both photocatalysts demonstrate superparamagnetic behavior at room temperature. The UV–vis diffuse reflectance spectra of the photocatalysts confirm that all the heterostructured photocatalysts are responsive to visible light. The photocatalytic activity of the heterostructured photocatalysts was evaluated for the degradation of methylene blue (MB) and methyl orange (MO) in aqueous solution over the photocatalysts under visible light irradiation. The heterostructured photocatalysts prepared in this study exhibit highly efficient visible-light-driven photocatalytic activity for the degradation of MB and MO, and they can be easily recovered by applying an external magnetic field.     

Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

Mg_xCu_3−xV₂O₆(OH)₄·2H₂O (x ∼ 1), with similar crystal structure as volborthite Cu₃V₂O₇(OH)₂·2H₂O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few mL of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO₄ to trigonal bipyramidal VO₅, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu₃V₂O₈ phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu₃V₂O₈ phases.     

Study of the dielectric properties in the NaNbO3 -KNbO3-In2O3 system using AC impedance spectroscopy

We report a comparative study of the dielectric properties of solid-state (ceramic method) synthesized NaNbO₃ (NN), Na_0.75K_0.25NbO₃ (K25NN), K_0.5Na_0.5NbO₃ (KNN) and some composite materials containing In₂O₃ and NN or KNN using an AC impedance method. Powder X-ray diffraction (PXRD) was employed to investigate the phase purity. No significant amount of impurity phase was observed for NN, K25NN, and KNN. Substitutions of 10, 15 and 25 mol% In³⁺ for Nb⁵⁺ in KNN and NN using solid-state reactions at 1150 °C resulted in composite materials. AC impedance studies of NN, KNN and K25NN in the temperature range of 500-800 °C showed a single semicircle (attributed to the bulk property) in the high-frequency range of 10³ to 10⁶ Hz. The individual contributions from the bulk and grain boundary on the dielectric properties were resolved and quantified from the impedance data. The calculated dielectric values for NN were consistent with previously reported in the literature. 10% Indium based KNN composite materials had the lowest dielectric loss 0.585 and the dielectric constant of 233 at 100 kHz at the temperature of 650 °C.     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.     

An oxides-hydrothermal approach from bulky V2O5 powder to V3O7·H2O nanoribbons or V3O7 nanoflowers in various ethanol/water mixed solvent

V₃O₇·H₂O nanoribbons and V₃O₇ nanoflowers are firstly obtained via facile oxides-hydrothermal (O-HT) route. V₂O₅ bulk-phase powder is directly used as precursor. The 1:1 ethanol/water and absolute ethanol are made as solvent for obtaining nanomaterials of vanadium oxides with different morphologies and structures. Characterizations of the samples are carried out using XRD, TG, FTIR, Raman-Spectra, SEM, TEM, HRTEM, SAED, and UV-vis. The large-scale fine ribbon-like V₃O₇·H₂O nanobelts with thickness ca. 20 nm and length ca. 20-40 μm are obtained in 1:1 (v/v) ethanol/water mixed solvent. The V₃O₇ nanoflowers are constructed by numerous whisker-like nanocrystal or petal-like are obtained in absolute ethanol solvent with the thickness about 20 nm and the size ca. 2-3 μm. The formation mechanism of the sample is discussed.     

Synthesis and characterization of Bi2Fe4O9 powders

Bi₂Fe₄O₉ have been successfully prepared using ethylenediaminetetraacetic (EDTA) acid as a chelating agent and ethylene glycol as an esterification agent. Heating of a mixed solution of EDTA, ethylene glycol, and nitrates of iron and bismuth at 140 °C produced a transparent polymeric resin without any precipitation, which after pyrolysis at 250 °C was converted to a powder precursor for Bi₂Fe₄O₉. The precursors were heated at 400–800 °C in air to obtain Bi₂Fe₄O₉ powder and differential scanning calorimetry (DSC), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques were used to characterize the precursors and the derived oxide powders. XRD analysis showed that well-crystallized and single-phase Bi₂Fe₄O₉ with orthorhombic symmetry was obtained at 700 °C for 2 h and BiFeO₃ and Fe₂O₃/FeCO₃ were intermediate phases before the formation of Bi₂Fe₄O₉. Bi₂Fe₄O₉ powders show weak ferromagnetism at room temperature.