A simple method to synthesize single-crystalline β-wollastonite nanowires

The single-crystalline β-wollastonite (β-CaSiO₃) nanowires were prepared via a simple hydrothermal method, in the absence of any template or surfactant using cheap and simple inorganic salts as raw materials. Xonotlite [Ca₆(Si₆O₁₇)(OH)₂] nanowires were first obtained after hydrothermal treatment at a lower temperature of 200 °C for 24 h, and after being calcinated at 800 °C for 2 h, xonotlite nanowires completely transformed into β-wollastonite nanowires and the wire-like structure was preserved. The synthesized β-wollastonite nanowires had a diameter of 10–30 nm, and a length up to tens of micrometers, and the single-crystalline monoclinic parawollastonite structured β-wollastonite was identified by XRD with the space group of P2₁/a and cell constants of a=15.42 Å, b=7.325 Å, c=7.069 Å and β=95.38°. A possible growth mechanism of β-wollastonite nanowires was also proposed. The advantages of this method for the nanowire synthesis lie in the high yield, low temperature and mild reaction conditions, which will allow large-scale production at low cost.     

Simple hydrothermal preparation of -MnOOH nanowires and their low-temperature thermal conversion to β-MnO2 nanowires

Without the use of any extra surfactant or template, γ-MnOOH single crystalline nanowires were synthesized directly through the hydrothermal reaction between KMnO₄ and toluene in distilled water at 180 °C for 24 h; and β-MnO₂ single crystalline nanowires could be obtained just by calcination of the γ-MnOOH nanowires in air at 280 °C for 5 h. The as-prepared γ-MnOOH and β-MnO₂ nanowires were characterized by X-ray powder diffraction, atomic absorption spectroscopy, Fourier transformed infrared spectroscopy, scanning electron microscope, transmission electron microscope, high-resolution transmission electron microscope and selected area electron diffraction.     

Synthesis and characterization of volatile metal β-diketonate chelates of M(DPM)n (M=Ce, Gd, Y, Zr, n=3,4) used as precursors for MOCVD

High pure Ce(DPM)₄, Gd(DPM)₃, Y(DPM)₃ and Zr(DPM)₄ (DPM=dipivaloylmethanate=2,2,6,6-tetramethyl-3,5-heptanedionato) powders were successfully synthesized from inorganic salts and HDPM in ethanol/aqueous solution followed by recrystallization from toluene. Freshly prepared samples have been characterized by elemental analysis, X-ray diffraction, thermogravimetry-differential thermal analysis, nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Aged samples, obtained by exposing fresh ones into air for 30 days, were also represented. Various structures, stabilities and volatilities result from different metal atoms and coordination numbers. Those metal β-diketonate chelates are served as precursors of metalorganic chemical vapor deposition for single and multi-component oxide thin films.     

The photoluminescence of ZnO thin films grown on Si (1 0 0) substrate by plasma-enhanced chemical vapor deposition

High-quality ZnO thin films have been grown on a Si(1 0 0) substrate by plasma-enhanced chemical vapor deposition (PECVD) using a zinc organic source (Zn(C₂H₅)₂) and carbon dioxide (CO₂) gas mixtures at a temperature of 180°C. A strong free exciton emission with a weak defect-band emission in the visible region is observed. The characteristics of photoluminescence (PL) of ZnO, as well as the exciton absorption peak in the absorption spectra, are closely related to the gas flow rate ratio of Zn(C₂H₅)₂ to CO₂. Full-widths at half-maximum of the free exciton emission as narrow as 93.4 meV have been achieved. Based on the temperature dependence of the PL spectra from 83 to 383 K, the exciton binding energy and the transition energy of free excitons at 0 K were estimated to be 59.4 meV and 3.36 eV, respectively.     

Growth and spectral properties of Nd:LaVO4 crystal

This paper reports the growth and spectral properties of 3.5 at% Nd³⁺:LaVO₄ crystal with diameter of 20×15 mm² which has been grown by the Czochralski method. The spectral parameters were calculated based on Judd–Ofelt theory. The intensity parameters Ω_λ are: Ω₂=2.102×10⁻²⁰ cm², Ω₄=3.871×10⁻²⁰ cm², Ω₆=3.235×10⁻²⁰ cm². The radiative lifetime τ_r is 209 μs and calculated fluorescence branch ratios are: β₁(0.88μm)=45.2, β₂(1.06μm)=46.7, β₃(1.34μm)=8.1. The measured fluorescence lifetime τ_f is 137 μm and the quantum efficiency η is 65.6%. The absorption band at 808 nm wavelength has an FWHM of 20 nm. The absorption and emission cross sections are 3×10⁻²⁰ and 6.13×10⁻²⁰ cm², respectively.     

Selective-controlled synthesis of one-dimensional strontium phosphates

Anorthic SrHPO₄ nanobelts and hexagonal Sr₁₀O(PO₄)₆ nanorods were obtained by a simple hydrothermal method without adding any surfactant as template. The as-synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM and HRTEM observations of the products revealed that the as-prepared SrHPO₄ nanobelts and Sr₁₀O(PO₄)₆ hexagonal nanorods are single crystals with their preferential growth direction along the normal of (1 0 0) and (0 0 1) planes, respectively.     

Synthesis, thermal and magnetic properties of new metal iodate: (LiFe1/3)(IO3)2

This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe_1/3)(IO₃)₂, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6₃.     

Growth and spectral properties of Nd-doped Sr3Y(BO3)3 crystal

A new crystal of Nd³⁺:Sr₃Y(BO₃)₃ with dimension up to 25×35 mm² was grown by Czochralski method. Absorption and emission spectra of Nd³⁺: Sr₃Y(BO₃)₃ were investigated . The absorption band at 807 nm has a FWHM of 18 nm. The absorption and emission cross sections are 2.17×10⁻²⁰ cm² at 807 nm and 1.88×10⁻¹⁹ cm² at 1060 nm, respectively. The luminescence lifetime τ_f is 73 μs at room temperature     

The growth and spectroscopic characteristics of Ca3Y2(BO3)4:Er laser crystal

The Ca₃Y₂(BO₃)₄:Er³⁺ crystal with a size up to 20 mm×30 mm was grown by the Czochralski method. The absorption spectrum was measured and its absorption peaks were assigned to the corresponding transitions between the Er³⁺ energy levels. A broad emission spectrum from 1429.4 to 1662.8 nm was exhibited from 530 nm wavelength pumping. This crystal is promising as a tunable infrared laser crystal.     

Hydrothermal synthesis of MoS2 nanowires

The MoS₂ nanowires with diameters of 4 nm and lengths of 50 nm were synthesized by a hydrothermal method using 0.36 g MoO₃ and 1.8 g Na₂S as precursors in 0.4 mol/l HCl solution at 260°C. The products are characterized by XRD, XPS, TEM, HTEM and BET. Results show that the as-prepared MoS₂ nanowires consist of 1–10 sulfide layers with BET surface areas of 107 m²/g. The possible reaction route and the formation mechanism of the MoS₂ nanowires are discussed. The effects of exterior conditions such as pH value, temperature, concentration of precursors and additives on the particle size and morphology of MoS₂ crystallites were investigated.     

Facile synthesis of submicron BaTiO3 crystallites by a liquid–solid reaction method

Uniform, submicron BaTiO₃ crystallites in tetragonal structure were synthesized by a novel low-temperature liquid–solid reaction method mainly via two simple steps: firstly, BaO₂·H₂O₂ submicron particles of about 130–450 nm were precipitated from the reaction of BaCl₂ and H₂O₂ in a slightly alkaline (pH 8) aqueous solution under the ambient condition; secondly, tetragonal phase BaTiO₃ submicrocrystals with the size in the range of 180 to 400 nm could be produced by subjecting the as-prepared BaO₂·H₂O₂ and commercial TiO₂ submicron particles to thermal treatment in air at 700 °C for 10 h. The as-obtained products were characterized by X-ray powder diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectroscopy, and scanning electron microscopy.     

Growth of SiC nanowires within stacked SiC fiber fabrics by a noncatalytic chemical vapor infiltration technique

An atmospheric pressure chemical vapor infiltration (CVI) process without metallic catalysts was applied for the growth of SiC nanowires within stacked SiC fiber fabrics. We investigated the effect of the concentration of a reactant gas (CH₃SiCl₃, MTS) on the growth behavior and microstructure of the SiC nanowires. At high concentration of MTS in a H₂+MTS mixture gas, one-dimensional (1D) SiC deposits with diameters of several hundreds of nanometers were formed. Microstructures of the 1D SiC deposits exhibited a strong positional dependency throughout the thickness direction of the stacked fabric due to a depletion of the MTS gas. On the other hand, single-crystalline SiC nanowires with average diameters of 50–60 nm could be obtained at a low concentration of MTS. The SiC nanowires also exhibited a homogeneous growth both in the plane of each fabric layer and throughout the thickness of the sample.     

Formation of single-crystal γ-MnO2 nanowires at room temperature

In this study, single-crystal γ-MnO₂ nanowires have been successfully synthesized at room temperature in the absence of catalysts or templates, the diameter was found to be ca. 10–20 nm and the characteristic lengths up to several micrometers. The crystal phase of nanowires was confirmed by XRD and TEM measurements. Further, a dissolution– condensation–recrystallization process was proposed for the formation of nanowires under the room temperature condition.     

Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide

The hydrothermal carbonation of calcium hydroxide (Ca(OH)₂) at high pressure of CO₂ (initial P_CO2=55 bar) and moderate to high temperature (30 and 90 °C) was used to synthesize fine particles of calcite. This method allows a high carbonation efficiency (about 95% of Ca(OH)₂–CaCO₃ conversion), a significant production rate (48 kg/m³ h) and high purity of product (about 96%). However, the various initial physicochemical conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals. The present study is focused on the estimation of the textural properties of synthesized calcite (morphology, specific surface area, average particle size, particle size distribution and particle size evolution with reaction time), using Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer–Emmett–Teller (BET) measurements, and scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. This study demonstrate that the pressure, the temperature and the dissolved quantity of CO₂ have a significant effect on the average particle size, specific surface area, initial rate of precipitation, and on the morphology of calcium carbonate crystals. In contrast, these PTx conditions used herein have an insignificant effect on the carbonation efficiency of Ca(OH)₂.

Finally, the results presented here demonstrate that nano-calcite crystals with high specific surface area (S_BET=6–10 m²/g) can be produced, with a high potential for industrial applications such as adsorbents and/or filler in papermaking industry.     

Synthesis of Y2O3:Eu phosphors by bicontinuous cubic phase process

A novel approach for preparation of red-emitting europium-doped yttrium oxide phosphor (Y₂O₃:Eu) by using the bicontinuous cubic phase (BCP) process was reported in this paper. The BCP system was composed of anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and aqueous yttrium nitrate/europium nitrate solution. Energy dispersive spectrometer analysis revealed the homogeneous precipitation occurred in the BCP structure. Thermogravimetric analysis measurements indicated the precursor powder was europium-doped yttrium hydroxide, Y_1−xEu_x(OH)₃. Scanning electron microscopy micrographs showed the precursor powder had a primary size about 30 nm and narrow size distribution. After heat treatment in furnace above 700 °C for 4 h, high crystallinity Y₂O₃:Eu phosphors was obtained. However, the primary size of particles grew to 50–200 nm and the dense agglomerates with a size below 1 μm were formed. X-ray diffraction patterns indicated the crystal structure of precursor powders and Y₂O₃:Eu phosphors were amorphous and body-centered cubic structure, respectively. The photoluminescence analysis showed that the obtained Y₂O₃:Eu phosphor had a strong red emitting at 612 nm and the quenching started at a Eu concentration of 10 mol%. This study indicated that the BCP process could be used to prepare the highly efficient oxide-based phosphors.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Growth of nanowires from annealing SiBONC nanopowders

Silicon carbide (SiC) nanowires were prepared by the gas pressure annealing of SiBONC powders, which were synthesized by pyrolysis of a polymeric precursor. The yield, morphology and composition of the nanowires were influenced by the Si/B ratio in the original ceramic powders, annealing temperature and atmosphere. Annealing temperatures between 1500 and 1600 °C and Si/B molar ratios between 70:30 to 60:40 were suitable for growth of the nanowires. When annealing in an argon (Ar) atmosphere, the SiC nanowires contained little oxygen (O); and the diameters ranged from 20 to 200 nm. Then annealing in a nitrogen (N₂) atmosphere, the nanowires were thicker and rougher, and consisted of a relatively high level of nitrogen. Varied shapes and morphologies of the nanowires were observed for different synthesis conditions. The present novel method makes possible the large-scale fabrication of β-SiC nanowires.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

Preparation and characterization of Ni-incorporated FeS2 single crystals

Nickel-incorporated FeS₂ single crystals with various Ni compositions of Fe_0.99S₂:Ni_0.01, Fe_0.98S₂:Ni_0.02, Fe_0.96S₂:Ni_0.04, and Fe_0.9S₂:Ni_0.1 were grown by chemical vapor transport (CVT) method using ICl₃ as a transport agent. Physical properties of the Ni-incorporated FeS₂ single crystals were characterized using X-ray diffraction, Raman spectroscopy, electrical conductivity, and photoconductivity (PC) measurements. By means of the analyses of the X-ray diffraction patterns, the whole series of Ni-doped FeS₂ single crystals were determined to be single-phase and isostructural. Raman spectroscopy of the Ni-doped FeS₂ crystals was carried out at room temperature. Raman resonant peaks of the Ni-doped FeS₂ crystals demonstrate an energy red-shift behavior with respect to the increase of the dopant densities. Conductivity measurements show the resistivity of the Ni-doped FeS₂ decreased as the doping concentration of Ni is increased. Nickel is an n-type dopant, which behaves like a donor level existed near the conduction band edge of the synthetic FeS₂. On the other hand, dopant effect of nickel on the synthetic FeS₂ also destroys the photoconductive sensitivity in the photoconductivity measurements.     

Synthesis and characterization of type-II textured tungsten disulfide thin films by vdWR process with Pb interfacial layer as texture promoter

The growth of type-II textured tungsten disulfide (WS₂) thin films by solid state reaction between the spray deposited WO₃ and gaseous sulfur vapors with Pb interfacial layer has been studied. X-ray diffraction (XRD) technique is used to measure the degree of preferred orientation ‘S’ and texture of WS₂ films. Scanning electron microscopy (SEM) and transmission electron microscopy techniques have been used to examine the microstructure and morphology. The electronic structure and chemical composition were studied using X-ray photoelectron spectroscopy (XPS). The use of Pb interfacial layer for the promotion of type-II texture in WS₂ thin films is successfully demonstrated. The presence of (0 0 3 l), (where l=1, 2, 3, …) family of planes in the XRD pattern indicates the strong type-II texture of WS₂ thin films. The crystallites exhibit rhombohedral (3R) structure. The large value of ‘S’ (1086) prompts the high degree of preferred orientation as well. The stratum of crystallites with their basal plane parallel to the substrate surface is seen in the SEM image. The EDS and XPS analyses confirm the tungsten to sulfur atomic ratio as 1:1.75. We purport that Pb interfacial layer enhances type-II texture of WS₂ thin films greatly.