Evaluation of thermodynamic and kinetic stability of CuAlO<Subscript>2</Subscript> and CuGaO<Subscript>2</Subscript>

Thermodynamic and kinetic stabilities of CuAlO₂ and CuGaO₂ have been evaluated by using thermogravimetry and thermodynamic calculations. It has been revealed that CuAlO₂ and CuGaO₂ are not thermodynamically stable in air below 800 °C and 1,200 °C, respectively, and that the oxidation reaction, 4CuMO₂ + O₂ → 2CuO + 2CuM₂O₄ (M = Al, Ga), should occur if the reaction kinetics are high enough. However, rate constants and activation energies indicated slow kinetics of the oxidation reaction, showing kinetic stability of CuMO₂ even under some thermodynamically unstable temperatures and atmospheres. It was also concluded that CuAlO₂ showed higher thermodynamic and kinetic stability than CuGaO₂.     

One-step template-free solution route for Cu(OH)<Subscript>2</Subscript> nanowires

Cu(OH)₂ nanowires with a diameter of 8–10 nm and lengths of tens of micrometers were fabricated in the basic solution by dropping simply NaOH solution into CuCl₂ solution at ambient temperature. The formation mechanism of nanowires was discussed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the samples. This article was submitted by the authors in English.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Preparation of CuAlO<Subscript>2</Subscript> thin films with high transparency and low resistivity using sol–gel method

CuAlO₂ thin films were deposited on quartz substrates by sol–gel process using copper acetate monohydrate and aluminum nitrate nanohydrate as starting materials and isopropyl alcohol as solvent. The influence of annealing temperature on the film structure and the phase evolution of CuAlO₂ films were investigated, so as to obtain CuAlO₂ films with superior performance. The phase compositions of the films were dependent on the annealing temperature. The films annealed at temperatures below 400 °C were amorphous while those annealed above 400 °C were polycrystalline. The phases of CuO and CuAl₂O₄ appeared gradually with the increase of annealing temperature. When the heat treatment temperature was elevated to 900 °C, the uniform and dense films with single phase of CuAlO₂ were obtained, with a resistivity of 15 Ωcm. The transmittance of the 310 nm-thick CuAlO₂ film is 79% at 780 nm and the direct optical band gap is 3.43 eV.     

Metamagnetic DyAlO<Subscript>3</Subscript> nanoparticles with very low magnetic moment

Nanocrystalline dysprosium monoaluminate (DyAlO₃) has been synthesized by modified sol–gel method after sintering the precursor gel at 950 °C. The micro-structural features have been verified by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy. The XRD pattern confirms the formation of single-phase DyAlO₃; the average size of the nanoparticles is 50 nm. X-Ray photoelectron spectroscopy has been used to study the chemical composition and bonding in the samples. The binding energies of core-level electrons in Dy, Al and O in DyAlO₃ nanopowder have been found slightly shifted compared to the respective values of the same elements. Both AC and DC magnetic susceptibilities have been measured in the temperature range 2–300 K. Unusually low effective magnetic moment of Dy³⁺, μ_eff = 0.38, has been derived from the inverse magnetic susceptibility–temperature plot between 4 and 252 K. The Nèel temperature, T_N = 3.920 K and exchange interaction constant J/k = −1.74 K, have been also determined.     

Electrorheological property and microstructure of acetamide-modified TiO<Subscript>2</Subscript> nanoparticles

A sol–gel method has been proposed to prepare uniform TiO₂ nanoparticles whose average size is about 30 nm. The prepared nanometer TiO₂ particles are modified by acetamide via different self-assembled processes. X-ray diffraction analyses, scanning electron microscopy, and Fourier transform infrared spectrometry are used to determine the structure of the nanoparticles. The results indicate that the different synthesis processes do not change the morphology of the TiO₂/acetamide nanoparticles; nevertheless, they affect the interaction between amide and acetamide. The electrorheological (ER) activity is studied by shear stress under DC electric field. The acetamide-modified TiO₂ ER fluid shows notable ER activity with shear stress about 45 kPa (at 5 kV/mm), which outclasses the shear stress (2 kPa) of unmodified TiO₂ ER fluid. It is also found that the ER effect is very sensitive to the interaction of molecules on TiO₂ particles. The chemical bond between core and shell can enhance the ER activity of the sample.     

Fabrication parameter-dependent morphologies of self-organized ZrO<Subscript>2</Subscript> nanotubes during anodization

Zirconia (ZrO₂) nanotubes have been synthesized using a facile anodizing process in organic electrolyte systems containing a low content of fluoride. The nanotube architecture evolution was recorded at different anodization periods (1–24 h) by scanning electron microscopy. A compact layer was found between the Zr substrate and its upper tubular layer after 1 h of anodization, whereas after further anodization for 3 h the compact layer disappeared. Meanwhile, ZrO₂ nanotubes turned to a uniform structure from top to bottom. However, after 18–24-h-long anodization, the uniform tubular layer was replaced by a random layer composed of various structural defects. Since the compact layer was not completely dissolved, the retained compact layer yielded O-rings with double walls on the outer surface of the nanotubes.     

Preparation of nanocrystalline Fe-doped TiO<Subscript>2</Subscript> powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO₂ powders were prepared using TiOSO₄, urea, and Fe(NO₃)₃ · 9H₂O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO₂, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m²/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe³⁺ and Fe²⁺ have been detected on the surface of TiO₂ powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO₂ powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO₂ was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO₂ powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.     

Structural evolution and magnetic properties of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers by electrospinning

The SrFe₁₂O₁₉/poly (vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol-gel assisted electrospinning with ferric nitrate, strontium nitrate and PVP as starting reagents. Subsequently, the M-type strontium ferrite (SrFe₁₂O₁₉) nanofibers were derived from calcination of these precursors at 750–1,000 °C.The composite precursors and strontium ferrite nanofibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The structural evolution process of strontium ferrite consists of the thermal decomposition and M-type strontium ferrite formation. After calcined at 750 °C for 2 h the single M-type strontium ferrite phase is formed by reactions of iron oxide and strontium oxide produced during the precursor decomposition process. The nanofiber morphology, diameter, crystallite size and grain morphology are mainly influenced by the calcination temperature and holding time. The SrFe₁₂O₁₉ nanofibers characterized with diameters of around 100 nm and a necklace-like structure obtained at 900 °C for 2 h, which is fabricated by nanosized particles about 60 nm with the plate-like morphology elongated in the preferred direction perpendicular to the c-axis, show the optimized magnetic property with saturation magnetization 59 A m² kg⁻¹ and coercivity 521 kA m⁻¹. It is found that the single domain critical size for these M-type strontium ferrite nanofibers is around 60 nm.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Influence of YSZ buffer layer on the electric properties of compositionally graded (Ba,Sr)TiO<Subscript>3</Subscript> thin film

Compositionally graded Ba_1−x Sr _x TiO₃ (BST) (0 ≤ x ≤ 0.4) thin films were fabricated on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by a modified sol–gel technique. The YSZ buffer layer was prepared by RF magnetron sputtering. The microstructure of the graded BST films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that all the films have uniform and crack-free surface with a perovskite structure. The graded BST film with an YSZ buffer layer has larger dielectric constant and lower dielectric loss. The leakage current density of the graded BST film with an YSZ buffer layer lowers two orders than the film without buffer layer. The improved electric properties of the graded films with an YSZ buffer layer was attributed to the YSZ buffer layer act as an excellent seeding layer to enhance the graded BST film growth.     

Effect of heat treatment on particle growth and magnetic properties of electrospun Sr<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>11.8</Subscript>O<Subscript>19</Subscript> nanofibers

Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently, the M-type ferrite Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions. The precursor and resultant Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or the holding time prolonged to 12 h at 900 °C, the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology. The magnetic properties of the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized magnetic properties are achieved with the specific saturation magnetization 75.0 A m² kg⁻¹ and coercivity 426.3 kA m⁻¹ for the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers.     

Ammonia gas sensor based on a spinel semiconductor,Co<Subscript>0.8</Subscript>Ni<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanomaterial

Thick film of nanocrystalline Co_0.8Ni_0.2Fe₂O₄ was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co_0.8Ni_0.2Fe₂O₄. XRD of Co_0.8Ni_0.2Fe₂O₄ revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H₂S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia.     

Low-voltage anodized TiO<Subscript>2</Subscript> nanostructures studied by alternate current electrochemical microscopy and photoelectrochemical measurements

This paper presents the characterization of TiO₂ nanostructures obtained by low-voltage anodization using alternate current electrochemical microscopy (AC-SECM) and photoelectrochemical (PEC) measurements. TiO₂ nanostructures were obtained from the exposure of titanium foils to several aqueous acidic solutions of hydrofluoric acid + phosphoric acid at potentials of 1 to 3 V. Scanning electron microscopy, X ray diffraction, and atomic force microscopy studies evidence the formation of a thin porous amorphous layer (<600 nm) with pore size in the range of 200–1,000 nm. By AC-SECM studies at different bias, we were able to confirm the unambiguous semiconducting properties of as-obtained porous titania films, as well as differences in surface roughness and conductivity in specimens obtained at both potentials. The difference in conductivity persists in air annealed samples, as demonstrated by electrochemical impedance spectroscopy and PEC measurements. Specimens obtained at 3 V show lower photocurrent and dark current than those obtained at 1 V, regardless of their larger conductivity, and we proposed it is due to differences on the oxide layer formed at the pore bottom.     

N,B, Si-tridoped mesoporous TiO<Subscript>2</Subscript> with high surface area and excellent visible-light photocatalytic activity

N, B, Si-tridoped mesoporous TiO₂, together with N-doped, N, B-codoped and N, Si-codoped TiO₂, was prepared by a modified sol–gel method. The samples were characterized by wide-angle X-ray diffraction (WAXRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, UV–visible adsorbance spectra (UV–vis) and X-ray photoelectron spectra (XPS). The N, B, Si-tridoped mesoporous TiO₂ showed small crystallite size, large specific surface area (350 m²/g), uniform pore distribution (3.2 nm) and strong absorption in the visible light region. The photocatalytic activities of the samples were evaluated by the photodegradation of 2,4-dichlorophenol (2,4-DCP) aqueous solution. The N, B, Si-tridoping sample exhibited much higher photocatalytic activity compared with other synthesized photocatalysts. The high activity could be attributed to the strong absorption in the visible light region, large specific surface area, small crystallite size, large amount of surface hydroxyl groups, and mesoporosity.     

LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2−x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>2</Subscript> nanoparticles: synthesis,structure, and evaluation of electrochemical properties for lithium ion cell application

Layered Ti-doped lithiated nickel cobaltate, LiNi_0.8Co_{0.2 − x}Ti_xO₂ (where x = 0.01, 0.03, and 0.05) nanopowders were prepared by wet-chemistry technique. The structural properties of synthesized materials were characterized by X-ray diffraction (XRD) and thermo-gravimetric/differential thermal analysis (TG/DTA). The morphological changes brought about by the changes in composition of LiNi_0.8Co_{0.2 − x}Ti_xO₂ particles were examined through surface examination techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Electrochemical studies were carried out using 2016-type coin cell in the voltage range of 3.0–4.5 V (vs carbon) using 1 M LiClO₄ in ethylene carbonate and diethyl carbonate as the electrolyte. Among the various concentrations of Ti-doped lithiated nickel cobaltate materials, C/LiNi_0.8Co_0.17Ti_0.03O₂ cell gives stable charge–discharge features.     

Synthesis and characterization of ferroelectric SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> nanotubes arrays

Ferroelectric SrBi₂Ta₂O₉ nanotubes were fabricated by sol–gel dipping template technique and characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. They had a single orthorhombic perovskite structure, and most of SBT nanotubes showed highly preferential crystal growth along the [115] orientation. FE-SEM and TEM investigations showed that nanotubes have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. From HRTEM results, the clear lattice fringes indicated that the nanotubes are structurally uniform and well crystallized. The growth mechanisms of SBT nanotubes into the AAO templates were explored.     

Preparation and characterization of CuAlO2 transparent thin films prepared by chemical solution deposition method

CuAlO₂ thin films were prepared on quartz glass and sapphire substrates by chemical solution deposition method using copper acetate monohydrate, aluminum nitrate nonahydrate and 2-methoxyethanol as starting precursor and solvent. The effects of annealing temperature on the structural, morphological, electrical and optical properties have been studied. Via the optimized annealing treatment condition, CuAlO₂ film annealed at 850 °C in nitrogen flow of 400sccm under atmosphere pressure exhibits the best performance with the lowest room temperature resistivity of 3.6 × 10² Ω cm and the highest optical transmission in the visible region (>70% at around 600 nm wavelength). CuAl₂O₄ and CuO phases, not CuAlO₂ phase are obtained when annealing temperature is lower than 850 °C. However, a further increase of annealing temperature weakens the crystallization quality and deteriorates the surface morphology of CuAlO₂ films as the annealing temperature exceeds 850 °C, leading to an increase in the resistivity and a decrease of the optical transmission in the visible region of CuAlO₂ films.     

Oleic acid-assisted preparation of LiMnPO<Subscript>4</Subscript> and its improved electrochemical performance by Co doping

LiMnPO₄, with a particle size of 50–150 nm, was prepared by oleic acid-assisted solid-state reaction. The materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the materials were investigated by galvanostatic cycling. It was found that the introduction of oleic acid in the precursor led to smaller particle size and more homogeneous size distribution in the final products, resulting in improved electrochemical performance. The electrochemical performance of the sample could be further enhanced by Co doping. The mechanism for the improvement of the electrochemical performance was investigated by Li-ion chemical diffusion coefficient ( [(D)\tilde]_\textLi ) \left( {{{\tilde{D}}_{\text{Li}}}} \right) and electrochemical impedance spectroscopy measurements. The results revealed that the [(D)\tilde]_\textLi {\tilde{D}_{\text{Li}}} values of LiMnPO₄ measured by cyclic voltammetry method increase from 9.2 × 10⁻¹⁸ to 3.0 × 10⁻¹⁷ cm² s⁻¹ after Co doping, while the charge transfer resistance (R _ct) can be decreased by Co doping.     

On the Formation of TiO<Subscript>2</Subscript> Nanoparticles Via Submerged Arc Discharge Technique: Synthesis,Characterization and Photocatalytic Properties

We report a simple and inexpensive synthesis route of TiO₂ nanoparticles using electrical arc discharge between titanium electrodes in oxygen bubbled deionized (DI) water followed by heat treatment. The resulting nanoparticles were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns demonstrate formation of TiO₂ phase in oxygen bubbled water after heat treatment and dominance of rutile to anatase phase. The size and morphology of TiO₂ nanoparticles were studied using different arc currents as a crucial parameter in properties of final product. Microscopic studies reveal nanosize spherical particles. DLS results indicate that at 20 A arc current, the size of the particles is about 37 nm and increases to 59 nm by increasing the arc current up to 40 A. Photodegradation of Rhodamine B (Rh. B) as a standard pollution shows that heat treated samples in oxygen bubbled water for 2 h at 500 °C, have more photocatalytic activity due to enhancement in crystallinity.