Preparation and characterization of pure single-phase BiFeO3 nanoparticles through thermal decomposition of the heteronuclear Bi[Fe(CN)6]·5H2O complex

The heteronuclear Bi[Fe(CN)₆]·5H₂O complex was synthesized and single-phase perovskite-type BiFeO₃ nanoparticles with an average size of 30 nm were obtained by its decomposition at 600 °C. The complex and its decomposition products were analyzed using elemental analysis, thermal analysis (TGA/DTA/DSC), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), UV–Vis spectroscopy, BET specific surface area measurement, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and magnetic measurements. The magnetic measurement confirms that the product shows a ferromagnetic order at room temperature, which may be ascribed to the size confinement effect. The DTA and DSC results confirm the multiferroic nature of the BiFeO₃ nanoparticles with Neel and Curie points at 372 and 825 °C, respectively. The BiFeO₃ prepared by this method could be an appropriate visible-light photocatalytic material due to its strong absorption band in the visible region. This method is simple, low-cost, safe and also suitable for industrial production of high purity perovskite-type BiFeO₃ nanoparticles for electromagnetic applications.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

Porous α-Fe2O3 hollow microspheres and their application for acetone sensor

Porous α-Fe₂O₃ hollow microspheres were synthesized through a simple and efficient carbon sphere template method. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption. Structural characterization indicated that as-prepared α-Fe₂O₃ hollow microspheres had porous structure with around 200 nm in diameter and thin shell about 10 nm thick. The average pore size and Brunauer-Emmett-Teller specific surface area of α-Fe₂O₃ hollow microspheres were 6.5 nm and 111.6 m²/g, respectively. The gas sensing behavior investigation showed that as-synthesized α-Fe₂O₃ hollow microspheres exhibited very good gas sensing property to acetone vapor.     

Low-temperature synthesis of K2NbO3F powders by an alternative approach of solid-state reaction

K₂NbO₃F powders were directly synthesized by an alternative solid-state method at low temperature. Stoichiometric ammonium niobium oxalate, K₂C₂O₄ and KF were mixed with small amounts of water and then dried at room temperature. X-ray diffraction results show that layered perovskite K₂NbO₃F powders can be obtained by calcining the mixture in temperature range from 550 to 700 °C for 3 h. The elemental composition, powder morphology and particle size of calcination products were analyzed by scanning electron microscope-energy dispersive spectroscopy (SEM/EDS). The SEM images suggest that the particles of the powders obtained at 550 °C are irregular platelets with a diameter of 0.5-1 μm and a thickness of 100-200 nm. The platelets are 3-5 μm in diameter and 1-2 μm in thickness when the calcination temperature reaches 700 °C. K₂NbO₃F decomposes to K₅(NbO₃)₄F and KF when the temperature reaches 800 °C.     

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4:Eu phosphors via sol-gel process

Europium-doped nanocrystalline GdVO₄ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO₂@Gd_0.95Eu_0.05VO₄ core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd_0.95Eu_0.05VO₄ layers begin to crystallize on the SiO₂ spheres after annealing at 600 ^°C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd_0.95Eu_0.05VO₄ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by ⁵D₀-⁷F₂ transition of Eu³⁺ (618 nm, red). The PL and CL intensities of Eu³⁺ increase with increasing the annealing temperature and the number of coating cycles. The optimum concentration for Eu³⁺ was determined to be 5 mol% of Gd³⁺ in GdVO₄ host.     

Sol-gel deposition and luminescent properties of LaMgAl11O19:Ce/Tb phosphor films

Rare earth ions (Ce³⁺, Tb³⁺)-doped LaMgAl₁₁O₁₉ phosphor films were deposited on quartz glass substrates by Pechini sol-gel and dip coating method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), field emission scanning electronic microscopy (FESEM), photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the magnetoplumbite structure LaMgAl₁₁O₁₉ phase can be obtained at 1200 °C on quartz glass substrates. This was further verified by the results of FT-IR and TG-DTA. AFM study showed that uniform films have an average grain size of 150 nm and a root mean square (RMS) roughness of 4 nm. The thickness of the films characterized by FESEM is about 340 nm. LaMgAl₁₁O₁₉:Ce³⁺ film showed the parity and spin allowed 5d-4f band emission of Ce³⁺ with a maximum at 350 nm. Ce³⁺, Tb³⁺-codoped LaMgAl₁₁O₁₉ films showed the band emission of Ce³⁺ and characteristic emission of Tb³⁺, namely, ⁵D_3,4-⁷F_J (J=6, 5, 4, 3) due to an efficient energy transfer from Ce³⁺ to Tb³⁺ in the host.     

Hydrothermal synthesis of cobalt carbonates using different counter ions: An efficient precursor to nano-sized cobalt oxide (Co3O4)

Synthesis of submicrometer crystalline particles of cobalt carbonate was achieved hydrothermally using different cobalt salts and urea with a molar ratio from 1:3 to 1:20 (cobalt salt:urea) in aqueous solutions at 160 °C for 24-36 h, in the presence of cetyltrimethylammonium bromide (CTAB) as a surfactant. Nanoparticles of Co₃O₄, with an average size from 30 to 39 nm, were obtained by thermal decomposition of CoCO₃ samples at 500 °C for 3 h in an electrical furnace. The as-synthesized products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-Vis spectra and thermal analysis. Studying the optical properties of the as-prepared cobalt oxide nanoparticles showed the presence of two band gaps, the values of which confirmed the semiconducting properties of the prepared Co₃O₄.     

Thermal decomposition route for synthesis of Mn3O4 nanoparticles in presence of a novel precursor

The synthesis of manganese oxide (Mn₃O₄) nanoparticles by using thermal decomposition and its physicochemical characterization are being reported in present investigation. As a new precursor, [bis(2-hydroxy-1-naphthaldehydato)manganese(II)] complex was used in the presence of oleylamine (C₁₈H₃₇N) as both surfactant and solvent to control the size of resulting nanoparticle. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. Synthesized manganese oxide nanoparticles have a tetragonal structure with average size of 9–24 nm. The phase pure samples were characterized by using X-ray photoelectron spectroscopy (XPS) for Mn 2p level. The values of binding energies are consistent with the relative values are reported in the literature. As a comparison between two methods, the novel precursor thermally was treated in solid state reaction in different temperature, 400, 500, and 600 °C and the products were characterized by SEM images. Magnetic property of the as-prepared Mn₃O₄ nanoparticle shows a ferromagnetic behavior with high saturation magnetization and coercivity.     

The effects of ZnGa2O4 formation on structural and optical properties of ZnO:Ga powders

Gallium-doped zinc oxide (ZnO:Ga 1, 2, 3, 4 and 5 at%) samples were prepared in powder form by modifying the Pechini method. The formation of zinc gallate (ZnGa₂O₄) with the spinel crystal structure was observed even in ZnO:Ga 1 at% by X-ray diffraction. The presence of ZnGa₂O₄ in ZnO:Ga samples was also evidenced by luminescence spectroscopy through its blue emission at 430 nm, assigned to charge transfer between Ga³⁺ at regular octahedral symmetry and its surrounding O²⁻ ions. The amount of ZnGa₂O₄ increases as the dopant concentration increases, as observed by the quantitative phase analysis by the Rietveld method.     

Synthesis of nano-sized crystalline oxide ion conducting fluorite-type Y2O3-doped CeO2 using perovskite-like BaCe0.9Y0.1O2.95 (BCY) and study of CO2 capture properties of BCY

Formation of nano-sized Y₂O₃-doped CeO₂ (YCO) was observed in the chemical reaction between proton conducting Y₂O₃-doped BaCeO₃ (BCY) and CO₂ in the temperature range 700-1000 °C, which is generally prepared by wet-chemical methods that include sol-gel, hydrothermal, polymerization, combustion, and precipitation reactions. BCY can capture CO₂ of 0.13 g per ceramic gram at 700 °C, which is comparable to that of the well-known Li₂ZrO₃ (0.15 g per ceramic gram at 600 °C). Powder X-ray diffraction (PXRD), energy dispersive X-ray analysis (EDX), laser particle size analysis (LPSA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ac impedance spectroscopy were employed to characterize the reaction product obtained from reaction between BCY and CO₂ and subsequent acid washing. PXRD study reveals presence of fluorite-like CeO₂ (a=5.410 (1) Å) structure and BaCO₃ in reaction products. TEM investigation of the acid washed product showed the formation of nano-sized material with particle sizes of about 50 nm. The electrical conductivity of acid washed product (YCO) in air was found to be about an order higher than the undoped CeO₂ reported in the literature.     

Preparation and characterization of optical spectroscopy of Lu2O3:Eu nanocrystals

Nanoscale Lu₂O₃:Eu powders were prepared by solution combustion synthesis. X-ray diffraction (XRD), high-resolution electronic microscope (HREM), Fourier transform infrared spectroscopy (FT-IR), excitation and emission spectra, as well as fluorescent decay curves were measured to characterize the structure and luminescent properties of the samples. The results show that the compound of composition Lu₂O₃ crystallizes in pure cubic structure. By changing the ratio of glycine to nitrate in the combustion process, the particle size varies from 40 nm to less than 5 nm. The emission and excitation spectra strongly depend on the particle size of the samples. Novel emission band, red-shift of charge transfer band (CTB) and shortening of lifetime were observed in nanoscale samples.     

Photocatalytic activity of ZrO2 nanoparticles prepared by electrical arc discharge method in water

ZrO₂ nanoparticles were synthesized through arc discharge of zirconium electrodes in deionized (DI) water. X-ray diffraction (XRD) analysis of the as prepared nanoparticles indicates formation a mixture of nanocrystalline ZrO₂ monoclinic and tetragonal phase structures. Transmission electron microscopy (TEM) images illustrate spherical ZrO₂ nanoparticles with 7–30 nm diameter range, which were formed during the discharge process with 10 A arc current. The average particle size was found to increase with the increasing arc current. X-ray photoelectron spectroscopy (XPS) analysis confirms formation of ZrO₂ at the surface of the nanoparticles. Surface area of the sample prepared at 10 A arc current, measured by BET analysis, was 44 m²/g. Photodegradation of Rhodamine B (Rh. B) shows that the prepared samples at lower currents have a higher photocatalytic activity due to larger surface area and smaller particle size.     

Microstructure and luminescence of transparent glass ceramic containing Er:BaF2 nano-crystals

Transparent BaF₂-SiO₂ glass ceramics doped with different content of Er³⁺ were prepared by sol-gel method. The microstructural evolution of the samples was studied with X-ray diffraction (XRD), transmission electron microscope (TEM), absorption and infrared spectra (IR). BaF₂ nano-crystals with 2-15 nm in size, depending on the crystallization temperature, distributed homogeneously among the amorphous silica matrix. The BaF₂ lattice parameters decreased with the increasing of Er³⁺ doping, indicating the incorporation of Er³⁺ into nano-crystals, which was further confirmed by energy dispersive X-ray spectroscopy (EDS) and absorption spectra analysis. The upconversion emissions of Er³⁺ emerged under the excitation at 980 nm for glass ceramic heat-treated at 800 °C.     

Preparing nanometer scaled Tb-doped Y2O3 luminescent powders by the polyol method

Sub-micrometer Tb-doped Y₂O₃ luminescent powders were prepared from nitrate precursors using the polyol method. Just after precipitation, the powders consist of agglomerates with a spherical shape and a size ranging between 400 and 500 nm. Each agglomerate is composed of ultra-small crystallites (from 3 to 6 nm) of a bcc oxide phase whose luminescence presents original features in comparison with bulk materials. Powders were further calcinated at different temperatures and for annealing below 900 °C, highly crystalline samples with the classical green ⁵D₄→⁷F₅ luminescent transitions of Tb³⁺ ions are obtained. For optimized annealing temperatures, sintering between the agglomerates is avoided and a sub-micrometric powder with a narrow size distribution and a high luminescence is obtained.     

Synthesis of nanospherical Fe3BO6 anode material for lithium-ion battery by the rheological phase reaction method

This paper developed a novel method, the rheological phase reaction method, to synthesize nanospherical Fe₃BO₆. The sizes and morphologies of products vary with the calcination temperatures. Spherical particles with a uniform size about 40 nm in a monodisperse state were obtained at 800 °C, while the spherical particles with a larger size of 100-500 nm were obtained at 900 °C. The electrochemical properties of these Fe₃BO₆ nanospheres were investigated. Sample synthesized at 800 °C delivers a high reversible capacity above 500 mAh g⁻¹. Sample synthesized at 900 °C possesses relatively good cycleability with a capacity retaining of 376 mAh g⁻¹ after 10 cycles. The measurement of electrochemical impedance spectra for the first time indicated that smaller Fe₃BO₆ nanoparticles intend to give higher impedance of solid-electrolyte interface layer and lower charge-transfer impedance after the first discharge. Additionally, it can be speculated that the increase of resistance charge-transfer is the possible reason for the capacity fading during cycling.     

Efficient photoluminescence of Dy at low concentrations in nanocrystalline ZrO2

Nanocrystalline ZrO₂:Dy³⁺ were prepared by sol-gel and the structural and photoluminescence properties characterized. The crystallite size ranges from 20 to 50 nm and the crystalline phase is a mixture of tetragonal and monoclinic structure controlled by dopant concentration. Strong white light produced by the host emission band centered at ∼460 nm and two strong Dy³⁺ emission bands, blue (488 nm) and yellow (580 nm), under direct excitation at 350 nm were observed. The highest efficiency was obtained for 0.5 mol% of Dy³⁺. Emission is explained in terms of high asymmetry of the host suggesting that Dy³⁺ are substituted mainly into Zr⁴⁺ lattice sites at the crystallite surface. Luminescence quenching is explained in terms of cross-relaxation of intermediate Dy³⁺ levels.     

CTAB-Mn3O4 nanocomposites: Synthesis,NMR and low temperature EPR studies

We are reporting on the synthesis of Mn₃O₄ nanoparticles and CTAB-Mn₃O₄ nanocomposites via a sonochemical route using MnCl₂, ethanol, NaOH and CTAB. The crystalline phase was identified as Mn₃O₄. The crystallite size of the CTAB-Mn₃O₄ nanocomposite was identified as 13 ± 5 nm from X-ray line profile fitting and the particle size from TEM was 107.5 ± 1.4 nm. The interaction between CTAB and the Mn₃O₄ nanoparticles was investigated by FTIR and ¹H NMR spectroscopies. Two different magnetic phase transitions were observed for both samples below the Curie temperature (43 °C) by using a low temperature Electron Paramagnetic Resonance (EPR) technique. Also we determined the effect of the capping with CTAB on the reduction in absorbed power.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

Synthesis of MnOOH nanorods by cluster growth route from [Mn12O12(RCOO)16(H2O)n] (R=CH3, C2H5). Rational conversion of MnOOH into Mn3O4 or MnO2 Nanorods

Single-crystalline nanorods of γ-MnOOH (manganite) phase with diameters of 120 nm and lengths of 1100 nm have been prepared using a new cluster growth route under low-temperature hydrothermal conditions starting from [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄]·2CH₃COOH·4H₂O or [Mn₁₂O₁₂(C₂H₅COO)₁₆(H₂O)₃]·4H₂O without any catalyst or template agents. The so-obtained nanorods were studied by X-ray diffraction (XRD), infrared (IR) spectroscopy, Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Their thermal conversion opens an access to Mn₃O₄ (hausmannite) and β-MnO₂ (pyrolusite) nanorods, respectively, under argon or air atmosphere. A coercive field of 12.4 kOe was obtained for the Mn₃O₄ nanorods.     

Flash microwave synthesis of trevorite nanoparticles

Nickel ferrite nanoparticles have several possible applications as cathode materials for rechargeable batteries, named “lithium-ion” batteries. In this study, NiFe₂O₄ was prepared by microwave induced thermohydrolysis. The obtained nanoparticles were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), BET method, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). All the results show that the microwave one-step flash synthesis leads in a very short time to NiFe₂O₄ nanoparticles with elementary particles size close to 4-5 nm, and high specific surfaces (close to 240 m²/g). Thus, microwave heating appears as an efficient source of energy to produce quickly nanoparticles with complex composition as ferrite.