Synthesis of titanate nanostructures using amorphous precursor material and their adsorption/photocatalytic properties

This article reports on a new and swift hydrothermal chemical route to prepare titanate nanostructures (TNS) avoiding the use of crystalline TiO₂ as starting material. The synthesis approach uses a commercial solution of TiCl₃ as titanium source to prepare an amorphous precursor, circumventing the use of hazardous chemical compounds. The influence of the reaction temperature and dwell autoclave time on the structure and morphology of the synthesised materials was studied. Homogeneous titanate nanotubes with a high length/diameter aspect ratio were synthesised at 160 °C and 24 h. A band gap of 3.06 ± 0.03 eV was determined for the TNS samples prepared in these experimental conditions. This value is red shifted by 0.14 eV compared to the band gap value usually reported for the TiO₂ anatase. Moreover, such samples show better adsorption capacity and photocatalytic performance on the dye rhodamine 6G (R6G) photodegradation process than TiO₂ nanoparticles. A 98% reduction of the R6G concentration was achieved after 45 min of irradiation of a 10 ppm dye aqueous solution and 1 g L⁻¹ of TNS catalyst.     

Instabilities in crystallization and magnetic behavior of Fe-Si-B amorphous alloys

Experimental evidence is presented to support the idea that the boron content, which influences the Fe-Fe pair distances and the electronic structure, determines the magnetic properties of amorphous Fe-Si-B alloys. Magnetic moment variations are ascribed to the local environment of the iron atoms and to the electronic structure of the amorphous Fe-Si-B alloys while the T_c changes are due to the increase of the Fe-Fe pair distances. The mean atomic magnetic moments per iron atoms were extrapolated at 0 K. Radial Distribution Analysis combined with Rietveld refinement achieved an estimation of Fe-Fe distances in amorphous and partially crystallized specimens, while the peculiarities in crystallization were revealed by HRTEM.     

Synthesis and gas sensing characteristics of SnO2 “dandelions”

SnO₂ dandelions-like architectures that composed of numerous one-dimensional tetragonal prism nanorods were synthesized by a simple hydrothermal method with the help of the surfactant poly(vinyl pyrrolidone) (PVP). The structure and morphology of resulting samples were characterized by means of X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results show that diameter of as-synthesized nanorods are less than 50 nm. The sensors fabricated from the SnO₂ nanorods exhibited good sensitivity, high selectivity and rapid response and recovery times to ethanol vapors at 280 °C.     

The application of freestanding titanate nanofiber paper for scattering layers in dye-sensitized solar cells

A titanate nanofiber paper with robust and good flexible property was successfully prepared by alkali hydrothermal synthesis with simple paper-making method. These nanofibers were about 80 nm in diameter and had a typical length in the range of tens of micrometers. Despite the transformation from titanate to TiO₂-B phase was initially started, such nanofiber paper still kept its original shape and good flexibility after calcinations at 450 °C for 30 min. A solar cell with titanate nanofiber paper as scattering layer yielded an overall conversion efficiency of 4.90% under an incident solar energy of 100 mW/cm², about 27.5% higher than that without nanofiber paper.     

Solvothermal synthesis and characterization of ZrO2 nanostructures using zirconium precursor

Zirconia (ZrO₂) is an important metal oxide owing to its applications in a variety of fields. Herein, we report the solvothermal synthesis of ZrO₂ nanostructures including nanorods, linked nanorods, and nanosheets. Aqueous solutions of [Zr₆O₄(OH)₄(H₂O)₈(Gly)₈]·12Cl·8H₂O (CP-2) or a mixture of CP-2 and ZrOCl₂·8H₂O containing NaOH were employed as the zirconium sources while Triton X-100, Tween-80 and sodium dodecylsulfate (SDS) were included to modify the morphology of the final product. Single-phase monoclinic ZrO₂ nanostructures could be obtained by the solvothermal method at 200 °C for 24 h independent of the presence or absence of Triton X-100, Tween-80 and SDS. However, the addition of Triton X-100, Tween-80 and SDS influenced the morphology of the resulting ZrO₂ nanostructures without affecting the crystal phase of the product.     

Crystal growth and structure determination of K2TiO3: A five coordinate titanate

Long, needle-shaped single crystals of K₂TiO₃ were grown out of a reactive high temperature hydroxide melt. The structure was determined by single crystal X-ray diffraction and found to crystallize in the orthorhombic Cmcm space group with a = 10.0283(2) Å, b = 6.9346(2) Å, c = 5.4534(1) Å, V = 379.242(15) Å³, and Z = 4. The structure is related to the K₂SnO₃ and K₂ZrO₃ structures, which crystallize in the Pnma space group, and that of K₂PbO₃, which crystallizes in the Cmc2₁ space group. The structure consists of chains of trans edge-sharing TiO₅ rectangular pyramids with alternating apical directions. The chains are separated by KO₇ polyhedra.     

Boron induced recrystallization of amorphous silicon film by a rapid thermal process

Rapid thermal process (RTP) is to induce boron-doped amorphous silicon into a high degree of crystallization of polycrystalline silicon in 5 min. In addition to the short time characteristic, it also provides a relatively lower temperature route to prepare high percentage of polycrystalline silicon in comparison with solid phase crystallization method. Before RTP, boron is homogeneously doped into the amorphous silicon film by ion implantation technology. After rapid thermal processing, the grain size of the polycrystalline silicon was found about at 0.1-0.5 μm. The degree crystallization of silicon is reached up to 99.1% with a good hole mobility of 138.6 cm²/V s.     

Shape controlled synthesis of Cu2O and its catalytic application to synthesize amorphous carbon nanofibers

Octahedral Cu₂O particles and Cu₂O nanowires were synthesized by a simple solution-phase route using N₂H₄·H₂O as reducing agent at room temperature. Amorphous carbon nanofibers were synthesized using octahedral Cu₂O particles and an acetylene gas source at atmospheric pressure. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis. SEM and TEM images indicated that most of the obtained octahedral Cu₂O particles had an edge length of 400-700 nm. The obtained nanowires had uniform diameters of about 15 nm, and the length of the nanowires ranged from 5 to 10 μm. The XRD result revealed the amorphous feature of the nanofibers. IR spectrum revealed that the nanofibers consist of -CH, -CH_2, -CC- and -CH₃ groups. The concentrations of N₂H₄·H₂O and NaOH played important roles in controlling the geometric shape of the Cu₂O.     

Thermally induced structural transformations and their effect on functional properties of Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

The influence of thermal treatment on microstructure and functional properties of Fe_89.8Ni_1.5Si_5.2B₃C_0.5 amorphous alloy and their mutual correlations were studied. Structural transformations were identified using DSC and characterized using X-ray diffraction. The alloy was found to exhibit a wide supercooled liquid region before crystallization, while kinetic parameters of observed structural transformation indicated high complexity of these processes, involving simultaneous movement of large groups of atoms. Investigation of magnetic and electrical properties of the alloy showed that structural relaxation prior to crystallization affected both magnetic susceptibility and electrical resistivity of the alloy, leading to an increase in both, which can be correlated to a decrease in number of defects and an increase in free volume in the alloy sample, enabling greater mobility of magnetic domain walls, but also decreasing electron density of states at the Fermi level.     

Cu2S nanostructures prepared by Cu-cysteine precursor templated route

A facile Cu-cysteine precursor templated route for the synthesis of Cu₂S nanowires, dendritic-like and flowerlike nanostructures is reported. The Cu-cysteine precursors are prepared through the reaction between Cu²⁺, l-cysteine and ethanolamine at room temperature, and the morphologies of Cu-cysteine precursors can be controlled by adjusting the molar ratio of l-cysteine to Cu²⁺. The Cu-cysteine precursors are used as both templates and source materials for the subsequent preparation of polycrystalline Cu₂S nanostructures by thermal treatment, and the morphologies of the precursors can be well preserved after the thermal transformation to Cu₂S nanostructures. The samples are characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy.     

Generation of annularly symmetric periodic ferroelectric domains in Nd doped near stoichiometric LiTaO3 crystals by the vapor transport equilibration processing

Annually symmetric periodic ferroelectric domain and near stoichiometry have been generated simultaneously from Nd-doped congruent LiTaO₃ crystals by using the vapor transport equilibration (VTE) processing for the first time. The periodic width in the domain structure of 0.5 mol% Nd doped stoichiometric LiTaO₃ crystal was found to be about 70 μm, and the wavelength decreased with the increasing Nd concentration. It can be noticed by transmission spectra that VTE treated LT crystals shows blue shift as compared to congruent LT crystals. Also, various absorption bands were observed in Nd-doped LiTaO₃ crystals corresponding to the transitions from ⁴I_9/2 ground state of Nd³⁺ ions, indicating its potential in the self-lasing quasi-phase matching (QPM) applications.     

Flux growth of KGaP2O7 single crystals

Transparent potassium gallium pyrophosphate single crystals, KGaP₂O₇, have been grown by a spontaneous nucleation method using K₄P₂O₇-4KPO₃ as flux. The as-grown crystals were characterized by X-ray powder diffraction (XRPD), differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) techniques. The results show that the as-grown crystals were well crystallized and indexed in a monoclinic crystal system with space group P2₁/c. The crystal is stable in the measurement temperature range of 25-939.9 °C, and it melts congruently at 947 °C. The frequencies of the vibrational modes of the crystal were also obtained from measurements of the infrared spectrum.     

Agglomerates of amorphous carbon nanoparticles synthesized by a solution-phase method

A novel solution-phase method is developed for preparation of agglomerates of amorphous carbon nanoparticles under ambient atmosphere by the reaction of ferrocene and ammonium chloride in diglycol at 200 °C. Samples are characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. It is found that the nanoparticles are complete amorphous and agglomerate together due to the strong surface tension. The agglomerates of amorphous carbon nanoparticles with a diameter of 20-50 nm have a wide size distribution of mesopores with a Brunauer-Emmett-Teller surface area of 75.2 m² g^− 1. It is proposed that the dissolved reactants uniformly dispersing in the solutions could react at a molecular level to form uniform carbon nanoparticles.     

Improved nonvolatile holographic storage properties in Zr:Ru:Fe:LiNbO3 crystal by blue light recording

Lithium niobate crystal triply doped with zirconium, ruthenium and iron was grown by conventional Czochralski method and its nonvolatile storage characteristics were investigated by means of two-wavelength technology, where blue and red beam were used as recording and readout light, respectively. In oxidized Zr:Ru:Fe:liNbO₃ crystal, short response time of 9.1 s and high recording sensitivity of 0.92 cm/J were demonstrated, together with high fixed diffraction efficiency of 44.9% maintained. These excellent properties were attributed to the elimination of intrinsic defects by ZrO₂ doping and effective excitation of electrons by blue light. Our experimental results indicated this doped LiNbO₃ crystal was an outstanding medium for holographic storage applications.     

Influence of NH4Cl on the < 1 0 0> directed growth and properties of ADP crystal

Good quality, pure and ammonium chloride added < 1 0 0> directed ADP single crystals with different sizes were grown by Sankaranarayanan-Ramasamy method with the vision to improve the properties of the crystal. The grown crystals have cylindrical morphology and the crystals were subjected to UV-Vis., DTA, microhardness, laser damage threshold, dielectric, piezoelectric and SHG studies. The addition of ammonium chloride improves the quality and yields crystals with transparency more than 80% in minimum duration of growth. Higher laser damage threshold and mechanical stability were observed in ammonium chloride added ADP crystals. Low dielectric loss shows that the grown crystal contains minimum defects. Good piezoelectric behaviour was observed for the grown crystals. The SHG efficiency of the crystals was obtained using Nd-YAG laser, which is approximately 3 times that of pure ADP and shows the suitability of the ingot for nonlinear optical applications.     

Physicochemical properties of solid-solid interactions in nanosized NiO-substituted Fe2O3/TiO2 system at 1200 °C

The solid-solid interactions between nanosized pure and NiO-substituted ferric and titanium(IV) oxides have been investigated using XRD technique and microstructure studies, also magnetic properties were studied using vibrating samples magnetometer (VSM). The amounts of substituting Ni²⁺ were x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mole. A mixture equimolar proportions of finely powdered Fe₂O₃ and TiO₂ were mixed with NiO, ball milled, compressed at 250 kg/cm² and fired at 1200 °C for 4 h.The obtained results showed that with substituting Ni²⁺ concentration x = 0 only Fe₂TiO₅ phase is present (∼80 nm) which showed a very small saturation magnetic flux density (B_s), remnant magnetic flux density (B_r) and the maximum energy product (BH)_max. By the addition of x = 0.2 NiO, new phases were observed NiTiO₃ and NiFe₂O₄ of crystallite sizes 160 and 110 nm, respectively. By the increase of substituting Ni²⁺ concentration the NiTiO₃ and NiFe₂O₄ phases increased on the expense of Fe₂TiO₅ up to x = 0.4, then the increase in substituting Ni²⁺ concentration led to a decrease in Fe₂TiO₅ and NiTiO₃ while NiFe₂O₄ increases which results in a great improvement of magnetic properties.All samples exhibit a catalytic activity towards H₂O₂ decomposition and the values of rate constant increase with increasing amount of Ni²⁺ substituting. The most acidic active sites are shown by specimens substituted with x = 0 this concludes that H₂O₂ decomposition is not favored on acidic active sites.     

Effects of polarized excitation on the PJ manifolds emission in KYF4:Pr single crystal

A room temperature spectroscopic investigation on KYF₄:1.25 at%Pr³⁺ is presented. The effects on the optical properties of the multisite-disordered nature of the sample are studied and discussed. In particular we report on the broadening of the ³P_J absorption lines, at 10 and 300 K, and the 450–770 nm emissions as a function of observation and pump polarization. The evidence of a peculiar difference between emission under polarized excitation, parallel or orthogonal to the c axis, is shown. The ³P₀ lifetime was 45 μs in agreement with that measured in other fluoride hosts.     

Variable section ZnO nanostructures electrodeposited by dynamic polarization currents

In this work we propose a single procedure for the electrochemical growth of variable section, self-assembled ZnO columns by dynamic polarization currents instead of the conventional potentiostatic/galvanostatic procedures. A flexible ITO electrode was submerged in 5 mM ZnCl + 0.1KCl and the ZnO structures were formed by galvanodynamic current ramps. Some of the structures analyzed showed columns with variable sections and others showed hollow columns. The possibility of modifying the section would enhance the properties of ZnO nanostructured layers, since this would increase the specific area and the light-capturing capacity of solar devices and sensors.     

Micromechanical properties of amorphous carbon coatings deposited by different deposition techniques

Amorphous carbon coatings about 20 nm thick are commonly used as an overcoat on magnetic thin-film rigid disks and tape and disk head surfaces to improve their wear performance. In this study, we deposited amorphous carbon coatings with thicknesses ranging from 20 to 400 nm on single-crystal silicon substrates by four deposition processes: cathodic arc, ion beam deposition, r.f.-plasma-enhanced chemical vapor deposition, and r.f. sputtering. R.f.-sputtered SiC coatings were also deposited for comparison. The hardness, elastic modulus, and scratch resistance of these coatings were measured by nanoindentation and microscratching using a nanoindenter. The cathodic arc carbon coatings followed by sputtered SiC coatings exhibited the highest hardness, elastic modulus, scratch resistance/adhesion, and residual compressive stresses. The critical load, a measure of the scratch resistance/adhesion of the coating, increases with thickness. The cathodic arc coatings of lower thicknesses (˜ 30 nm) exhibited instant damage when the normal load exceeded the critical load, whereas thick coatings (greater than or equal to 100 nm) exhibited gradual damage through the formation of tensile cracks. The sputtered carbon coatings exhibited damage to the coating at very low loads and ploughing of the tip into the coating occurred right from the beginning of the scratch.     

Multilayer antireflective and protective coatings comprising amorphous diamond and amorphous hydrogenated germanium carbide for ZnS optical elements

To effectively protect and improve the transmittance of ZnS optical elements in the far infrared band, combined amorphous diamond (a-D) and amorphous hydrogenated germanium carbide (a-Ge_1−xC_x:H) films have been developed. The optical interference coatings were designed according to the layer optics theory. The a-D films, of which refractive index and film thickness were controlled by changing substrate bias and deposition time respectively, were deposited by filtered cathodic vacuum arc technology. The a-Ge_1−xC_x:H films were prepared by radio frequency sputtering technology. During this process their refractive index was modulated by changing the gas flow rate ratio and their film thickness was controlled by the flow rate ratio and deposition time. It has been shown that the combined films are superexcellent antireflective and protective coatings for ZnS optical elements.