Synthesis of transparent BaTiO<Subscript>3</Subscript> nanoparticle/polymer hybrid

Transparent BaTiO₃ nanoparticle/polymer hybrid was synthesized by polymerization and hydrolysis of barium titanium alkoxide modified with 2-vinyloxyethoxy ligand. Barium alkoxide, titanium alkoxide and 2-vinyloxyethanol were reacted affording a BaTiO₃ precursor, which was then hydrolyzed and polymerized to form BaTiO₃ particle/polymer hybrids below 100°C. BaTiO₃ particles increased in crystallinity with increasing water amount for hydrolysis. The absorption edge of the hybrid film on silica plates shifted to shorter wavelength with decreasing crystallite size. Nano-sized BaTiO₃ particle/polymer hybrid polymerized with methyl methacrylate (MMA) was shaped into a transparent and self-standing film with a refractive index of 1.595 at 589 nm.     

Electrical characterization of the [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>][N(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>]ZnCl<Subscript>4</Subscript> compound

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed an orthorhombic system with P2₁2₁2 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz, respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified. Dielectric data were analyzed using the complex electrical modulus M ^* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of a non-exponential decay function ϕ(t) = exp[(−t/τ) ^β ]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process. The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law.     

Structural and sensing properties of nanocrystalline SnO<Subscript>2</Subscript> films deposited by spray pyrolysis from a SnCl<Subscript>2</Subscript> precursor

We report the fabrication and characterization of tin dioxide gas sensing layers. The tin dioxide layers were synthesized using a convenient, simple and low-cost technique of spray pyrolysis. The formation of stoichiometric SnO₂ layers with fine-grain structure is revealed by Rutherford backscattering spectroscopy. The microstructure, phase, nanoparticle size distribution and surface morphology were studied by transmission electron microscopy, electron diffraction and atomic force microscopy. Most of the grains were of 10–20 nm size; however, some particles were up to 100 nm in size and had a microtwin lamellae structure of SnO₂ phase (cassiterite) with lattice parameters a= 0.474 nm and c= 0.319 nm. The sensitivity of the layers with respect to 1000–10000 ppm CH₄ in air was obtained from both resistivity (S_R) and capacity (S_C) measurements at 330 °C and values of S_R=5–7 and S_C=22–31 were extracted. PACS 68.43.-h; 68.55.-a; 81.05.Hd; 81.07.-b; 81.15.Rs     

Dielectric and polar order behaviors of BaTiO<Subscript>3</Subscript>-Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics

New perovskite solid solution ceramics of (1−x)BaTiO₃-xBi(Mg_1/2Ti_1/2)O₃ ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features of ferroelectrics with diffuse phase transition, though the temperature T _m of their dielectric constant maximum ε _m is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Effects of BaTiO<Subscript>3</Subscript> and SrTiO<Subscript>3</Subscript> as the buffer layers of epitaxial BiFeO<Subscript>3</Subscript> thin films

BiFeO₃ (BFO) thin films with BaTiO₃ (BTO) or SrTiO₃ (STO) as buffer layer were epitaxially grown on SrRuO₃-covered SrTiO₃ substrates. X-ray diffraction measurements show that the BTO buffer causes tensile strain in the BFO films, whereas the STO buffer causes compressive strain. Different ferroelectric domain structures caused by these two strain statuses are revealed by piezoelectric force microscopy. Electrical and magnetical measurements show that the tensile-strained BFO/BTO samples have reduced leakage current and large ferroelectric polarization and magnetization, compared with compressively strained BFO/STO. These results demonstrate that the electrical and magnetical properties of BFO thin films can be artificially modified by using a buffer layer.     

Characterization of Y<Subscript>2</Subscript>BaCuO<Subscript>5</Subscript> nanoparticles synthesized by nano-emulsion method

Nanoscale yttrium–barium–copper oxide (Y₂BaCuO₅, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant content, and surfactant/n-octane ratio affected the droplet size which was in the range of 3–8 nm, and hence the w/o emulsion system was referred to as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y₂(NO₃)₃) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM, and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using the nano-emulsion method was in the range of 30–100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K.     

PLD and RF-PLD synthesis of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films for electrically controlled devices

Ba_0.6Sr_0.4TiO₃ (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.     

Surface photovoltage properties and photocatalytic activities of nanocrystalline CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> particles with porous superstructure fabricated by a modified chemical coprecipitation method

In this study, nanocrystalline CoFe₂O₄ particles with porous timber-like superstructure were synthesized by a modified chemical co-precipitation route with calcination temperatures of 573, 673, 773, 873, and 973 K, respectively. The structural properties of the samples were systematically investigated by X-ray powder diffraction, scanning electronic microscopy, energy-dispersive X-ray spectra, UV–Vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the CoFe₂O₄ samples were comparatively studied by the degradation of 4-chlorophenol under Xe lamp irradiation. The results indicated that the sample calcined at 673 K exhibited the highest photocatalytic efficiency among the five samples.     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

HgO-added YB<Subscript>a2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>−δ superconductors

The HgO-added YB_a2Cu₃O_7−δ (YBCO) superconductor has been studied for its structural and superconducting properties. Polycrystalline YBCO samples were synthesized through solid-state reaction method by adding HgO in different concentrations without using oxygen annealing. All the samples showed a sharp superconducting transition temperature around 90 K. The X-ray diffraction patterns of all the samples revealed monophasic Y-123 nature. The structural studies were carried out by neutron scattering and Rietveld analysis. The neutron scattering revealed that Hg is not incorporated in the Y-123 system and has shown optimum oxygen concentration. The significant role played by the HgO is to provide oxygen ambient through its decomposition, thus changing the oxygen balance in favour of high Cu-valence state.     

Influence of Sm<Superscript>3+</Superscript> ion in structural,morphological, and electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by microwave calcination

LiSm_xMn_2–xO₄ samples were synthesized via co-precipitation technique. The structural properties of the synthesized materials were studied using X-ray diffraction analysis and it confirmed the cubic spinel structure for all the compounds. The lattice parameter of LiMn₂O₄ was observed to be 8.2347 Ǻ and it decreased with Sm³⁺ concentration, due to the shrinkage in cell volume aided by higher binding energy between Sm-O bond. The SEM micrographs were analyzed using Image processing software (Image-J) to ascertain the pore and grain properties. The microwave synthesis had been observed to control the bulk grain formation and had yielded lesser porous and nanoparticles. The particle size distributions obtained through photocross correlation laser diffraction analysis had shown that LiMn₂O₄ with 60 nm and Sm-doped compounds with ∼30 nm, respectively. The cyclic voltammetry studies had revealed the decrease in electrocatalytic behavior in the initial cycle for compounds doped with Sm³⁺ ion. The initial capacities of LiMn₂O₄, LiSm_0.05Mn_1.95O₄ and LiSm_0.10Mn_1.90O₄ substituted compounds were observed to be 134.87 mAhg⁻¹, 132.22 mAhg⁻¹ and 126.41 mAhg⁻¹, respectively. The cells were simulated using 1D model namely Dualfoil5.1 program. The simulated results coincide well with the measured results. The cycle life studies reveal 93% capacity retention of samarium-0.05-doped samples when compared with 78.4% of the LiMn₂O₄.     

Synthesis,characterization and magnetic properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanotubes

Well-aligned Co₃O₄ nanotubes were synthesized within the nanochannels of porous anodic alumina membranes using a single-source chemical vapor deposition method. Scanning electron microscopy and transmission electron microscopy showed that the Co₃O₄ nanotubes are highly ordered with uniform diameter in the range of 100–300 nm and length up to tens of microns. X-ray diffraction, the Raman spectrum, energy-dispersive spectroscopy and selected-area electron diffraction demonstrated that the nanotubes are composed of pure cubic phase polycrystalline Co₃O₄. Magnetic measurements using a SQUID magnetometer suggested the presence of a strong antiferromagnetic interaction with Weiss constant θ= -248 K. The real and imaginary parts of the ac susceptibility at f= 10 Hz had a maximum at 4.0 K, and the field dependence of the magnetization at 1.8 K showed a small hysteresis loop with a coercivity of ∼ 98 Oe. PACS 81.07.De; 81.15.Gh; 78.30.-j; 75.75.+a; 61.46.Np     

Synthesis of nanocrystalline SnO<Subscript>2</Subscript> in supercritical water

Nanocrystalline SnO₂ was synthesized in supercritical water at 385–415°C and 30 MPa (38–106 s residence time) in a tubular flow reactor from an aqueous solution of 0.1–0.4 M SnCl₄. The conversion rate was between 53 and 81%, but increased to 97.8% when 0.1 M NaOH was added. Nanoparticles were analyzed by a series of independent analytical techniques, including TEM, Raman, XRD, SEM, EDX and FT-IR. The initial size of the particles was about 3.7 nm. After calcination at 450°C for 2 h, the particle size increased to 4 nm. The particles were of low crystallinity, as indicated by the weak Raman and XRD signals. All particles were composed of Sn and O, as verified by the EDX spectra. The crystals were tetragonal, as confirmed by the weak XRD spectrum. After calcination at 600°C for 10 h, the particle size increased to 9 nm, while high crystallinity was confirmed by Raman and XRD analyses. All the crystals had the same structure, as indicated by TEM electron diffraction patterns. Using this one-step supercritical water process, nanoparticles of SnO₂ can be conveniently produced continuously in a flow reactor in less than 2 min.     

Magnetic state of the structural separated anion-deficient La<Subscript>0.70</Subscript>Sr<Subscript>0.30</Subscript>MnO<Subscript>2.85</Subscript> manganite

The results of neutron diffraction studies of the La_0.70Sr_0.30MnO_2.85 compound and its behavior in an external magnetic field are stated. It is established that in the 4–300 K temperature range, two structural perovskite phases coexist in the sample, which differ in symmetry (groups R[`3]cR\bar 3c and I4/mcm). The reason for the phase separation is the clustering of oxygen vacancies. The temperature (4–300 K) and field (0–140 kOe) dependences of the specific magnetic moment are measured. It is found that in zero external field, the magnetic state of La_0.70Sr_0.30MnO_2.85 is a cluster spin glass, which is the result of frustration of Mn³⁺-O-Mn³⁺ exchange interactions. An increase in external magnetic field up to 10 kOe leads to fragmentation of ferromagnetic clusters and then to an increase in the degree of polarization of local spins of manganese and the emergence of long-range ferromagnetic order. With increasing magnetic field up to 140 kOe, the magnetic ordering temperature reaches 160 K. The causes of the structural and magnetic phase separation of this composition and formation mechanism of its spin-glass magnetic state are analyzed.     

Preparation of TiO<Subscript>2</Subscript>-coated LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by electrostatic self-assembly method and its properties

A precursor of TiO₂–LiCo_1/3Ni_1/3Mn_1/3O₂ was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO₂-coated material can be indexed by α-NaFeO₂ layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO₂ compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was improved.     

Dielectric and phase transition of BaTi<Subscript>0.6</Subscript>Zr<Subscript>0.4</Subscript>O<Subscript>3</Subscript> ceramics prepared by a soft chemical route

BaTi_0.6Zr_0.4O₃ (BTZ) ceramic was synthesized by a soft chemical route. X-ray diffraction at room temperature shows that the sample has cubic perovskite structure with space group Pm-3m. Temperature dependent dielectric study of the sample has been investigated in the frequency range from 50 Hz to 1 MHz. The density of the sample was determined using Archimedes’ principle and found to be ∼ 97% of the X-ray density. The average grain size in the pallet was found to be ∼ 1 μm. The dielectric constant peaks at temperature T_m which is dependent on the frequency. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy = 0.0185 eV, and freezing temperature = 186 K. All these measurements confirm that BTZ is a relaxor ferroelectric. PACS 77.22.Jp; 77.84.-s; 77.80.Bh; 77.22.Gm     

Luminescence properties of transparent ceramics Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Yb

We present the results of studying the luminescence properties of transparent ceramics Y₃Al₅O₁₂:Yb obtained by the vacuum sintering and nanocrystalline technology. In the course of research, we measured the luminescence and luminescence excitation spectra, as well as the temperature and kinetic behavior of luminescence. Our results are analyzed in comparison with the characteristics of corresponding single crystals. We revealed that processes of generation and relaxation of electronic excitations that occur in ceramics, in particular, in the charge transfer state, are similar to processes occurring in crystals. The behavior of two charge-transfer luminescence bands at 340 and 490 nm is studied. In the range 300–600 nm, we revealed a broad emission band of radiation of other type, which is also observed in spectra of undoped ceramics. This broad band is attributed to F⁺ centers. Emission and excitation spectra of charge transfer luminescence at a maximum of the temperature dependence of 100 K are measured for the first time. We found that, upon excitation in the charge transfer band, luminescence in ceramics is more intense than in single crystals with similar concentrations of Yb and has a higher quenching temperature.     

Phase transition and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)(Nb<Subscript>1-x</Subscript>Ta<Subscript>x</Subscript>)O<Subscript>3</Subscript> lead-free piezoelectric ceramics

(K_0.5Na_0.5)(Nb_1-xTa_x)O₃ lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta⁵⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO₃, the (K_0.5Na_0.5)(Nb_1-xTa_x)O₃ ceramics can be sintered at higher temperatures. The partial substitution of Ta⁵⁺ for the B-site ion Nb⁵⁺ decreases both paraelectric/cubic–ferroelectric/tetragonal and ferroelectric/tetragonal–ferroelectric/orthorhombic phase transition temperatures, T_C and T_O-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become ‘softened’, leading to improvements in d₃₃, k_p, k_t and ε_r and a decease in E_c, Q_m and N_p. The ceramics with x=0.075–0.15 become optimum, having d₃₃=127–151 pC/N, k_p=0.43–0.44, k_t=0.43–0.44, ε_r=541–712, tanδ=1.75–2.48% and T_C=378–329 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s