Fabrication of BaTiO3 nanoparticles and its formation mechanism using the high temperature mixing method under hydrothermal conditions

Barium titanate (BaTiO₃) single-crystalline nanoparticles have been prepared via high temperature mixing method (HTMM) under hydrothermal conditions. The crystallized products were characterized by X-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), Raman spectra, transmission electron microscopy (TEM). The BaTiO₃ nanoparticles can be prepared at dilute KOH as compared with the method mixed at room temperature. The results show that the stoichiometric BaTiO₃ nanoparticles were synthesized at [Ba/Ti]_solution = 1. The high temperature will significantly narrow the solubility difference between the barium and titanium sources and leads to a burst nucleation from the solution. The defect mechanism is used to illustrate the time-dependent transformation from cubic to tetragonal phase.     

Characterization and synthesis of KTa0.1Nb0.9O3 particles via high temperature mixing method under hydrothermal conditions

KTa_0.1Nb_0.9O₃ (KTN) particles with an orthorhombic perovskite structure have been synthesized via a high temperature mixing method (HTMM) under hydrothermal conditions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influence of alkaline concentration and solvent composition on the phase structure and morphology of the obtained powders was investigated. The results show that the well-crystallized KTN powders with sizes of 200–500 nm are successfully prepared at temperatures as low as 240 °C when the KOH concentration is 2.0 M and the isopropanol/water (I/W) volume ratio equals to 100/0.     

Phase and morphology evolution of bismuth ferrites via hydrothermal reaction route

Phase-controlled synthesis of bismuth ferrites has been achieved via hydrothermal route by adjusting the KOH concentration. The as-prepared powders were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The particle morphologies of the as-prepared powders evolve from nanoflakes, to self-assembled particles, and microparticles when the concentration of KOH was changed from 1.5 M, 2.5 M, to 3.5 M, and 5 M. Correspondingly, the main phase of the samples changed from orthorhombic Bi₂Fe₄O₉, both Bi₂Fe₄O₉ and BiFeO₃, to pure rhombohedral BiFeO₃. On the basis of these experiments, the phase formation and morphology evolution mechanism of the samples are discussed. Furthermore, the photocatalytic activity of the as-prepared samples was investigated by the photo-degradation of rhodamine-B solution.     

Formation and Annealing of BaTiO_3 and SrTiO_3 Nanoparticles in KOH Solution

Barium titanate (BaTiO3) and strontium titanate (SrTiO3) nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba(OH)2 and Sr(OH)2 respectively, in 50 mol·dm-3 KOH solution at 150℃. Each structural evolution of BaTiO3 and SrTiO3 during the hydrothermal treatment was investigated by X-ray diffraction (XRD), field emission scanning elec- tron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM...     

La0.5Sr0.5TiO3 nanopowders prepared by the hydrothermal method

La_0.5Sr_0.5TiO₃ nanopowders were prepared by the hydrothermal method. The influence of processing parameters, including KOH concentration, reaction temperature and reaction time on the obtained products were studied. The structure and morphology of the obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that pure phase La_0.5Sr_0.5TiO₃ nanopowders can be successfully synthesized with 2 M KOH concentration at a low temperature of 220 °C for 24 h. In addition, the product has a plate-like shape with particle sizes in the range of 25–100 nm as estimated by TEM.     

Hydrothermal-polyol route to synthesis of β-Ni(OH)2 and NiO in mixed solvents of 1,4-butanediol and water

The β-Ni(OH)₂ with flower-like morphology assembled from nanosheets has been successfully synthesized by a hydrothermal-polyol method from Ni(CH₃COO)₂·4H₂O in mixed solvents of 1,4-butanediol and water at 200 °C for 24 h. The NiO with similar morphology was obtained by a simple thermal decomposition of the precursor (β-Ni(OH)₂) at 400 °C for 3 h in air. The products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TG) and differential scanning calorimetric analysis (DSC). We expect that this hydrothermal-polyol method may be extended to the preparation of nanostructures of other kinds of metal oxides.     

Photoluminescence properties of the In2O3 octahedrons synthesized by carbothermal reduction method

In₂O₃ octahedrons were synthesized by carbothermal reduction method. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction analysis (SAED) and room-temperature photoluminescence (PL) spectra. The results show that the products are single-crystalline In₂O₃ octahedrons with the arrises length in the range of 400-3000 nm. The PL spectra displays blue and green emission peaks which can be indexed to default and oxygen vacancies; blue-shift and intensity decrease was observed when excitation wavelength decreases from 380 nm to 325 nm. The growth mechanism of the In₂O₃ octahedrons is discussed.     

Hydrothermal synthesis of Fe3O4 nanoparticles and its application in lithium ion battery

Well dispersed Fe₃O₄ nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe₃O₄ as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g^− 1 at a current density of 0.1 mA cm^− 2.     

Synthesis of sphere-like Co3O4 nanocrystals via a simple polyol route

A simple polyol method was developed to synthesize uniform sphere-like Co₃O₄ nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co₃O₄ nanocrystals were spherical with the crystallite size in the range of 90-110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co₃O₄ nanocrystals. The magnetic properties of the Co₃O₄ nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.     

Fabrication and photoluminescence properties of large-scale hierarchical CdS dendrites

Large-scale hierarchical CdS dendrites were synthesized by a simple hydrothermal method using 3CdSO₄·8H₂O and SC(NH₂)₂ as the original reactant. X-ray powder diffraction, transmission electron microscopy, selected-area electronic diffraction and X-ray photoelectron spectroscopy were carried out to characterize the product. The room-temperature photoluminescence (PL) reveals that the as-prepared CdS products have visible emission of about 485, 561 and 617 nm, and an infrared red (IR) emission centered at 750 nm. The possible photoluminescence mechanisms are proposed in this report. The photoluminescence of CdS dendrites enables them to have great applications in optoelectronic devices.     

Microwave synthesis of SrCO3 one-dimensional nanostructures assembled from nanocrystals using ethylenediamine additive

One-dimensional SrCO₃ nanostructures assembled from nanocrystals have been successfully synthesized by a microwave-assisted aqueous solution method at 90 °C using Sr(NO₃)₂, (NH₄)₂CO₃ and ethylenediamine (C₂H₈N₂). Our experiments show that the microwave heating time plays an important role in the size and morphology of SrCO₃. A rational mechanism based on the oriented attachment self-assembly is proposed for the formation of SrCO₃ nanostructures. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). This method is simple, fast, low-cost and suitable for large-scale production of SrCO₃ nanostructures with different morphologies. We expect that this method may be extended to the preparation of nanostructures of other kinds of carbonates.     

Hydrothermal synthesis and characterization of CePO4/C core-shell nanorods

The CePO₄/C nanocomposite with core-shell nanostructure has been successfully synthesized using glucose and CePO₄ by a facile and simple hydrothermal method at 160 °C for 24 h. The new material consists of a monoclinic CePO₄ core and an amorphous-C shell. The TEM micrograph indicated that the CePO₄/C nanocomposite was core-shell nanorods. The effects of glucose concentration on the C shells and luminescent intensity of CePO₄/C nanocomposite were investigated. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). This method is simple, low-cost and does not need any surfactant.     

A simple route to synthesis of BaCO3 nanostructures in water/ethylene glycol mixed solvents

Barium carbonate (BaCO₃) nanostructures with different morphologies were synthesized using Ba(NO₃)₂ and (NH₄)₂CO₃ in the water/ethylene glycol (EG) mixed solvents by oil bath heating at 80 °C for 30 min. The molar ratio of water to EG had an effect on the morphology of BaCO₃. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM).     

Large-scale synthesis and characterization of fan-shaped rutile TiO2 nanostructures

Large-scale fan-shaped rutile TiO₂ nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl₄ as titanium source and chloroform/water as solvents. The physicochemical features of the fan-shaped TiO₂ nanostructures are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), nitrogen absorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTIR). Structural characterization indicates that the fan-shaped TiO₂ nanostructures are composed of several TiO₂ nanorods with diameters of about 5 nm and lengths of 300-350 nm. The average pore size and BET surface area of the fan-shaped TiO₂ nanostructures are 6.2 nm and 59 m²/g, respectively. Optical adsorption investigation shows that the fan-shaped TiO₂ nanostructures possess optical band gap energy of 3.11 eV.     

Coprecipitation-assisted hydrothermal synthesis of PLZT hollow nanospheres

Lanthanum-modified lead zirconate titanate Pb_1−xLa_x(Zr_1−yTi_y)O₃ (PLZT) hollow nanospheres have been successfully prepared via a template-free hydrothermal method using the well-mixed coprecipitated precursors and the KOH mineralizer. The structure, composition, and morphology of the PLZT hollow nanospheres were characterized by XRD (X-ray diffraction), ICP (inductive coupled plasma emission spectrometer), FTIR (Fourier transform infrared spectra), TG/DTA (thermogravimetric analysis and differential thermal analysis), TEM (transmission electron microscopy) and SEAD (selected area diffraction). The results show that the composition and the morphology control of the PLZT products are determined by the KOH concentration. The PLZT hollow nanospheres with uniform size of about 4 nm were synthesized in the presence of 5 M KOH. The crystalline nanoparticles can be prepared at dilute KOH, in contrast to the amorphous powders prepared at concentrated KOH. Formation mechanisms of the PLZT hollow nanospheres are also discussed.     

Microstructure and ferroelectric properties of epitaxial BaTiO3/SrRuO3/SrTiO3 (001) films grown by pulsed laser deposition under high oxygen pressure

BaTiO₃ films were epitaxially grown on SrTiO₃ (001) substrates buffered with SrRuO₃ films as bottom electrode by pulsed laser deposition under high oxygen pressure of 30 Pa. The quality of the BaTiO₃/SrRuO₃/SrTiO₃ multilayer films was analyzed by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy. BaTiO₃ films were found to be highly c-axis-oriented tetragonal phase with c/a = 1.002. The dielectric constant first increased with increasing temperature, and showed a peak at the Curie temperature of about 356 K. The films had well-saturated hysteresis loops with a remnant polarization of 7.3 μC/cm² and a coercive field of 29.5 kV/cm at room temperature.     

Self-assembly growth of BiFeO3 powders prepared by microwave-hydrothermal method

With FeCl₃·6H₂O and Bi(NO₃)₃·5H₂O powder as raw materials and KOH as a mineralizer, the pure phase BiFeO₃ (BFO) powder was synthesized by microwave-hydrothermal (MH) method at 200 °C, with the reaction time as little as 30 min. The range of preparing the BFO powders had been summarized. The field emission scanning electron microscopy (FE-SEM) images revealed that the little BFO plate grew together forming rock sugar-like BFO powders, and then they grew further to form the mussel-like BFO powders. The transmission electron microscope (TEM) images also improved the self-assembly growth of BFO powders. The X-ray diffraction (XRD), the high resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) results indicated that the BFO powders grew along the [110] and [104] crystal orientation. The B-H loops of BFO indicated that the weak magnetism existed in the pure phase BFO powders.     

Molten salt synthesis of single-crystal Co3O4 nanorods

The synthesis of the single-crystal Co₃O₄ nanorods by molten salt approach was reported for the first time. The products were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and Selected-area electron diffraction (SAED). TEM results indicate that these nanorods have diameters of about 150 nm and lengths of about 2 μm. According to the analysis of the SAED and HRTEM results, we drew the conclusion that these nanorods grew along an unusual [− 1,− 1,15] direction by Ostwald ripening mechanism.     

Synthesis of (K, Na)NbO3 particles by high temperature mixing method under hydrothermal conditions

In order to prepare the pure (K, Na)NbO₃(KNN) particles with higher crystallinity, the high temperature mixing method (HTMM) under hydrothermal conditions was carried out in this work. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). The results indicate that the KNN particles size decrease gradually with the increase of mineralization concentration in the starting solution. The ratio of K⁺/(K⁺ + Na⁺) in the starting solution has a great effect on the phase of the products, and several phases coexist in the product when the ratio of K⁺/(K⁺ + Na⁺) in the starting solution is 0.7.     

Facile hydrothermal route to the controlled synthesis of α-Fe2O3 1-D nanostructures

Single-crystalline α-Fe₂O₃ 1-D nanostructures can be obtained via a facile one-step hydrothermal synthetic route. It was found that the introduction of SnCl₄ played a key role in determining the composition and morphology of α-Fe₂O₃. The addition of SnCl₄ favours the formation of Fe₂O₃ rather than FeOOH, and the morphology can be tuned from nanorod to double-shuttle as the increase of SnCl₄ concentration. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). This simple method does not need any seed, catalyst, or template, thus is promising for large-scale and low-cost production.