Epitaxial growth of the CoFe2O4 film on SrTiO3 and its characterization

Cobalt ferrite (CoFe₂O₄) thin film is epitaxially grown on (0 0 1) SrTiO₃ (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe₂O₄ (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski–Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO₃ is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe₂O₄ film exhibits an enhanced out-of-plane magnetization (190 emu/cm³) with a large coercivity (3.8 kOe).     

Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

YBa₂Cu₄O₈ is a stoichiometric oxide superconductor of T_c80 K. Unlike YBa₂Cu₃O_7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T_c to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm³. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition.     

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.     

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.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Bi20TiO32 nanocones prepared from Bi–Ti–O mixture by metalorganic decomposition method

Bi₂₀TiO₃₂ in the form of nanocones are reported for the first time, which have been found during the formation of Bi₂Ti₂O₇ nanocrystals. Bi₂₀TiO₃₂ nanocones were prepared by metalorganic decomposition technique. From X-ray patterns, it was found that Bi₂₀TiO₃₂ is a metastable phase, and can transform gradually into Bi₂Ti₂O₇ phase with the annealing time increasing at a temperature of 550°C. The image of field emission scanning electron microscopy shows that the lengths of the nanocones are up to several micrometers and the diameters of cusps range from 20 to 200 nm. The studies of transmission electron microscopy show that the nanocones are crystalline Bi₂₀TiO₃₂. The growth mechanism of Bi₂₀TiO₃₂ nanocones has been proposed, which is similar to the vapor–liquid–solid growth mechanism.     

Synthesis of superparamagnetic Mn3O4 nanocrystallites by ultrasonic irradiation

Nanocrystalline Mn₃O₄ has been synthesized by ultrasonic irradiation of Mn acetate solution in water. Analysis of its X-ray diffraction data shows formation of a phase-pure compound with an average particle size of about 15 nm. DC magnetization measurements as a function of temperature and field show a reduced ferrimagnetic transition temperature as compared to those reported for the bulk , and a subsequent observation of superparamagnetic behavior at 40 K. The observed magnetic properties are suggestive of formation of a single domain magnetically ordered Mn₃O₄ nanoparticles below their ferrimagnetic transition temperature.     

Anisotropic vapor phase growth of Ga2O3 crystalline nanobelts

Ga₂O₃ nanobelts were synthesized by gas reaction at high temperature in the presence of oxygen in ammonia. X-ray diffraction and chemical microanalysis revealed that the nanostructures were Ga₂O₃ with the monoclinic structure. Electron microscopy study indicated the nanobelts were single crystalline with broad (0 1 0) crystallographic planes. The nanostructures grew anisotropically with the growth direction of . Statistical analysis of the anisotropic morphology of the nanobelts and electron microscopy investigation of the nanobelt tips indicated that both vapor–solid and vapor–liquid–solid mechanisms controlled the growth process. The anisotropic nature of crystallographic morphology is explained in terms of surface energy.     

Catalytic growth of In2O3 nanobelts by vapor transport

Indium oxide (In₂O₃) nanobelts have been fabricated by thermal evaporation of metallic indium powders with the assistance of Au catalysts. The as-synthesized nanobelts are single-crystalline In₂O₃ with cubic structure, and usually tens of nanometers in thickness, tens to hundreds of nanometers in width, and several hundreds of micrometers in length. The room temperature photoluminescence spectrum of In₂O₃ nanobelts features a broad emission band at 620 nm, which could be attributed to oxygen deficiencies in the as-synthesized belts. The formation of In₂O₃ nanobelts follows a catalyst-assistant vapor—liquid–-solid growth mechanism, which enables the controlled growth of individual belts on predetermined sites.     

Flux growth of BPO4 crystals

Single crystals of BPO₄ with sizes up to 15×10×12 mm³ were grown by top-seeded solution growth method using Li₂O–Li₄P₂O₇ as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO₄ was about 130 nm. Its density was 2.82 g/cm³ determined using drainage method.     

Crystallization behavior and hydrophilic performances of V2O5–TiO2 films prepared by sol–gel dip-coating

Homogeneous and transparent V₂O₅–TiO₂ composite nanometer thin films were prepared on glass substrates by sol–gel processing and dip-coating technique. The films as well as the dried powder of bulk gel were characterized by different techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscope (AFM) and thermogravimetry–differential thermal analysis (TG–DTA). The hydrophilicity of the films was determined by measuring the water contact angles on the films. The results showed that the dopant of V₂O₅ on TiO₂ thin films could produce a visible-light response to the films, and the introduction of V₂O₅ could suppress the structural phase transition and crystal growth of TiO₂ crystal. Finally, the relationship between crystalline size and hydrophilicity under sunlight was investigated in this article.     

Hydrothermal growth of single-crystal CaV6O16·3H2O nanoribbons

CaV₆O₁₆·3H₂O nanoribbons have been prepared by the hydrothermal method in the presence of sodium dodecyl sulfate (SDS) at 160°C for 10 h. X-ray diffraction pattern indicates that the sample is monoclinic phase of CaV₆O₁₆·3H₂O with the lattice contents a=12.18 Å, b=3.598 Å, c=18.39 Å, β=118.03°. Field emission scanning electron microscopy shows that the nanoribbons have widths in the range of 150–500 nm, thicknesses of 30–60 nm and lengths of 500 mm X-ray photoelectron spectrum measurements further confirm the formation of the CaV₆O₁₆·3H₂O phase. The formation of CaV₆O₁₆·3H₂O nanoribbons is a self-assembling process, in which surfactant SDS plays the role of soft template.     

Growth and morphology of ruby crystals with unusual chromium concentration

Single crystals of ruby have been obtained from fluxed melts based on the systems Li₂O–MoO₃, Li₂O–WO₃, Na₂O–WO₃, 2PbO–3V₂O₅, PbO–V₂O₅–WO₃, PbF₂–Bi₂O₃ and Na₃AlF₆ by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al₂O₃ solubility has been measured for the flux composition of 2Bi₂O₃–5PbF₂ in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.     

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     

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.     

Solvothermal synthesis of K2V3O8 nanorods

A solvothermal route has been developed to synthesize K₂V₃O₈ nanorods via the reduction of V₂O₅ using ethanol as the reducing agent as well as the solvent at 200°C. X-ray diffraction and selected area electron diffraction analysis revealed that the as-synthesized products are of tetragonal structure K₂V₃O₈. Transmission electron spectroscopy image showed that the obtained K₂V₃O₈ comprises rod-like nanocrystallites. The formation mechanism of K₂V₃O₈ was studied.     

Surface and interfacial structure of epitaxial SrTiO3 thin films on (0 0 1) Si grown by molecular beam epitaxy

Effects of relaxation of interfacial misfit strain and non-stoichiometry on surface morphology and surface and interfacial structures of epitaxial SrTiO₃ (STO) thin films on (0 0 1) Si during initial growth by molecular beam epitaxy (MBE) were investigated. In situ reflection high-energy electron diffraction (RHEED) in combination with X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS) and transmission electron microscopy (TEM) techniques were employed. Relaxation of the interfacial misfit strain between STO and Si as measured by in situ RHEED indicates initial growth is not pseudomorphic, and the interfacial misfit strain is relaxed during and immediately after the first monolayer (ML) deposition. The interfacial strain up to 15 ML results from thermal mismatch strain rather than lattice mismatch strain. Stoichiometry of STO affects not only surface morphology but interfacial structure. We have identified a nanoscale Sr₄Ti₃O₁₀ second phase at the STO/Si interface in a Sr-rich film.     

Effect of NH3 on the growth characterization of TiN films at low temperature

Titanium nitride (TiN) films were obtained by the atmospheric pressure chemical vapor deposition method of the TiCl₄–N₂–H₂ system with various flow rates of NH₃ at 600°C. The growth characteristics, morphology and microstructure of the TiN films deposited were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Without NH₃ addition, no TiN was deposited at 600°C as shown in the X-ray diffraction curve. However, by adding NH₃ into the TiCl₄–N₂–H₂ system, the crystalline TiN was obtained. The growth rate of TiN films increased with the increase of the NH₃ flow rate. The lattice constant of TiN films decreased with the increase of the NH₃ flow rate. At a low NH₃ flow rate, the TiN (2 2 0) with the highest texture coefficient was found. At a high NH₃ flow rate, the texture coefficient of TiN (2 0 0) increased with the increase of the NH₃ flow rate. In morphology observation, thicker plate-like TiN was obtained when the NH₃ flow rate was increased. When the flow rate of NH₃ was 15 sccm, Moiré fringes were observed in the TiN film as determined by TEM analysis. The intrinsic strain was found in the TiN film as deposited with 60 sccm NH₃.     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.