Synthesis,structure and optical properties of x(CuO)/(1−x)Ni(OH)2 [x=0, 0.1 and 0.3] nanocomposites

The x(CuO)/(1−x)Ni(OH)₂ [x=0, 0.1 and 0.3] nanocomposites were prepared by the hydrothermal method in the presence of the surfactant polyethylenglycol-10000 (PEG-10000). X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the as-prepared samples. The increase of the CuO content led to the increase of the crystallite size of both, the β-Ni(OH)₂ and the CuO. The increase in the crystallite size greatly affects the band gap energy of the as-prepared nanocomposites. The band gap energies of the x(CuO)/(1−x)Ni(OH)₂ nanocomposites were estimated by UV–vis spectroscopic method. UV–vis spectroscopic results showed an apparent decrease in the direct band gap energies. The x(CuO)/(1−x)Ni(OH)₂ [x=0, 0.1 and 0.3] nanocomposites show low band gap energies compared to the Ni(OH)₂ bulk materials. The enhanced optical properties lead to their possible use in photocatalytic and photovoltaic applications.     

Improvement of luminescent properties of GdPO4 doped with optimal europium concentration by Co-doping with lanthanum

Hexagonal gadolinium Phosphate Hydrate doped with different europium amounts (Gd_1-xPO₄:Eu_x·H₂O; x = 0.01, 0.05, 0.10, 0.15, and 0.20) was synthesized by hydrothermal synthesis method and the obtained samples were analyzed giving the optimal dopant concentration. Furthermore, gadolinium was additionally replaced by Lanthanum Gd_0.85-yLa_yPO₄:15%Eu (y = 0.25, 0.5, 0.75) in hopes of improving luminescence properties even more. This may be possible due to the fact that LaPO₄ exhibits a monoclinic crystal structure, which usually shows better luminescence properties. All of the synthesized compounds were analyzed by X-ray diffraction in order to investigate their crystal structure. SEM analysis was used to characterize the morphology of synthesized particles, while surface area and the pore size of Gd_0.85-xLa_xPO₄:15%Eu samples were measured using Nitrogen adsorption by the BET method and BJH method. The luminescence properties were also characterized and discussed in detail. Lastly, the cytotoxicity study demonstrated that the replacement of gadolinium with lanthanum leads to a reduction in the toxicity of the samples.     

Effect of Zr substitution on structural,magnetic, and optical properties of Bi0.9Dy0.1Fe1−xZrxO3 multiferroic ceramics prepared by rapid liquid phase sintering method

Zr substituted Bi_0.9Dy_0.1Fe_1−xZr_xO₃ (x=0.03, 0.06 and 0.10) multiferroic ceramics were synthesized by rapid liquid phase sintering technique to improve its multiferroic properties. Rietveld structural refinement of XRD patterns and Raman spectra revealed a partial structural phase transition from rhombohedral (R3c) to biphasic structure (R3c+P4mm) on codoping. The substitution of larger ionic radii and higher valence Zr⁴⁺ ions at Fe-site leads to decrease in the grain size as a result of charge compensation at Fe site. The weak ferromagnetic behavior were observed in all samples along with maximum M_r value of 0.159 emu/g for x=0.03 concentration, which is also endorsed by second order Raman modes. The distortion in FeO₆ octahedra due to Zr substitution leads to splitting of electronic bands of 3.2 eV into multiplets, which in turn reduced the optical band gap value in the range of 2.06–2.10 eV for all samples.     

Single step synthesis of tungsten carbide (WC) nanoparticles from scheelite ore

To prepare tungsten carbide (WC) nanoparticles high purity precursors like W, WO₃, WCl₄, WCl₆ and W(CO)₆ are used. Moreover, these precursors are obtained after high temperature and multistage processing of the ore. In this article a single step synthesis method is reported to get tungsten carbide (WC) nanoparticles directly from scheelite ore. The mixture of scheelite, activated charcoal and magnesium was heated for 20 h at 800 °C in an autoclave which led to the direct conversion of scheelite to nanocrystalline WC. The undesired reaction products and impurities (CaO, MgO and SiO₂) were washed firstly with dilute HCl (1:1) and then with base (0.25 M NaOH). The obtained powders were characterized by high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction.     

A new simple route for the preparation of nanosized copper selenides under different conditions

In this paper copper selenide nanostructures were synthesized via a simple hydrothermal method based on the reaction between copper salt and SeCl₄ in water. The reduction reaction of SeCl₄ to Se and then Se²⁻ was carried out by three types of reductants: N₂H₄.H₂O, KBH₄, and metallic Zn. Different compositions of copper selenides were obtained by changing the molar ratio of the precursors. At the temperature of 120 °C for a 12 h period of time, when the molar ratio of Cu/Se is 1:1 or 2:1, the product is pure and found to be CuSe and Cu_1.8Se, respectively. A mixture of the different phases of copper selenides is obtained by making use of 1:2, 3:2 and 3:1 M ratios between Cu and Se. With an increasing reaction temperature up to 210 °C, the mixture of Cu₃Se₂ and CuSe is prepared from 1:1 M ratio of precursors. The effects of copper salt, surfactant, amount of hydrazine, reaction time and temperature on the morphology and particle size of products are also investigated. The synthesis can be performed conveniently and safely. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. Photoluminescence (PL) is used to study the optical property of copper selenides.     

Synthesis and characterization of multiferroic BiFeO3 powders fabricated by hydrothermal method

The influence of processing parameters on phase formation and particle size of hydrothermally synthesized BiFeO₃ powders was investigated. BiFeO₃ powder was synthesized by dissolving bismuth nitrate and iron nitrate in KOH solution at temperatures ranging from 150 to 225 °C. X-ray diffraction patterns and scanning electron microscopy observation indicated that rod-like α-Bi₂O₃ phase was formed at initial stage of reaction and dissolved into ions to form thermodynamically stable BiFeO₃ phase. Single-phase perovskite BiFeO₃ has been formed using a KOH concentration of 8 M at a temperature of ≥175 °C in a 6 h reaction period. BiFeO₃ particle growth was promoted by lowering the KOH concentration, or increasing the duration time or reaction temperature. The effects of processing conditions on the formation of crystalline BiFeO₃ powders were discussed in terms of a dissolution–precipitation mechanism. The magnetization of the BiFeO₃ powders at room temperature showed a weak a ferromagnetic nature.     

Spin-glass behavior and redox catalytic properties of room temperature produced ZnCrMnO4

Recognizing the multifunctional capability of spinels, synthesis, and properties of oxide spinel with an equal concentration of Jahn Teller active Mn³⁺ and geometrically frustrated Cr³⁺ with non-magnetic Zn²⁺ have been explored. ZnCrMnO₄, resulting from the room temperature oxidation reaction, has an average crystallite size of 16 nm. Nearly 25% of Zn occupies the octahedral sites along with Cr and Mn, as revealed by the successful structural refinement in the Fd-3m space group. Electron microscopic results confirm cubic spinel formation. Raman spectrum shows the disordered nature of the spinel. X-ray photoelectron spectral (XPS) analysis establishes mixed valences of manganese ((III), (IV)) and chromium ((III) and (VI)). ZnCrMnO₄ displays electronic transitions typical of Mn³⁺ and Cr³⁺ in its UV–Visible diffuse reflectance spectrum. Spin-glass frustration at 26 K, followed by an antiferromagnetic ordering at 10 K, is noticed for the sample from the magnetic measurements. The sample exhibits a surface area of 138 m²/g (BET measurements) and catalyzes the oxidation of aromatic alcohols (phenol, benzyl alcohol) and reduction of nitroaromatics efficiently.     

Influence of surface treatments on topography and bond strength of densely-sintered zirconium-oxide ceramic

The aim of this study was to evaluate the effect of surface treatments on the roughness and bond strength of dental materials containing MDP to zirconium oxide ceramic. Forty square-shaped zirconium-oxide ceramic blocks (Lava Zirconia, 3M-ESPE) were treated as follows: (CT) polished only; (SB) sandblasting (110 µm aluminum oxide particles) or (SC) silica coating (110 µm particles). Roughness of treated surface was measured using a profilometer (Ra) and by atomic force microscope (AFM). Two resin luting agents were used after silane application: self-adhesive (Rely X U200, 3M-ESPE) and dual cure (Rely X Ultimate, 3M-ESPE). The samples were submitted to microshear bond strength test. The failure analysis was performed. Data were submitted to ANOVA and Tukey test (α=0.05). Bond strength results ranged from 20.44 (CT+Ultimate) to 34.37 MPa (SC+U200) after 24 h and from 12.03 (CT+Ultimate) to 27.44 MPa (SC+U200) after 12 months of storage with SC statistically superior to the other treatments. Mean values of roughness varied from 0.07 (CT) to 0.85 µm (SC). The both resin luting agents showed similar results to all surface treatment groups. Silica coating provided the best treatment of the ceramic surface.     

Structural,magnetic, vibrational and impedance properties of Pr and Ti codoped BiFeO3 multiferroic ceramics

Single-phase (Bi_1−xPr_x)(Fe_1−xTi_x)O₃ ceramics (x=0.03, 0.06, and 0.10 as BPFT-3, BPFT-6 and BPFT-10, respectively) were synthesized by conventional solid state reaction method. The effect of varying Pr and Ti codoping concentration on the structural, magnetic, dielectric and optical properties of the BPFT ceramics have been investigated. X-ray diffraction indicated pure rhombohedral phase formation for BPFT-3 and BPFT-6 ceramics, however, a structural phase transition from a rhombohedral to an orthorhombic phase has been observed for BPFT-10 ceramic. The maximum remnant magnetization of 0.1824 emu/g has been observed in BPFT-6. With increasing codoping concentration the room temperature dielectric measurements showed enhancement in dielectric properties with reduced dielectric loss. UV–vis diffuse reflectance spectra demonstrated the strong absorption of light in the visible region for a band gap variation 2.31–2.34 eV. Infrared spectroscopy indicated the shifting of Bi/Pr–O and Fe/Ti–O bonds vibrations and change in Fe/Ti–O bond lengths. Decrease in the conductivity on increasing Pr and Ti concentration in BFO is attributed to an enhancement in the barrier properties leading to suppression of lattice conduction path arising due to lattice distortion as confirmed from impedance analysis.     

Microstructure and physicomechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al₂O₃) nanocomposites containing CNT from 0.15 vol.% to 2.4 vol.% have been successfully fabricated by simple wet mixing of as-received commercial precursors followed by pressureless sintering. Extent of densification of nanocomposites sintered at low temperature (e.g. 1500 °C) was <90%, but increased up to ∼99% when sintered at 1700 °C and offered superior performance compared to pure Al₂O₃. Nanocomposites containing 0.3 vol.% MWCNT and sintered at 1700 °C for 2 h in Argon led to ∼23% and ∼34% improvement in hardness and fracture toughness, respectively, than monolithic Al₂O₃. In addition, the highest improvement (∼20%) in bending strength was obtained for 0.15 vol.% MWCNT/Al₂O₃ nanocomposite compared to pure Al₂O₃. Weibull analysis indicated reliability of nanocomposites increased up to 0.3 vol.% MWCNT, whereas, beyond that loading consistency was the same as obtained for pure Al₂O₃. Detailed microstructure and fractographic analysis were performed to assess structure-property relationship of present nanocomposites.     

Structure and electrical properties of Ca2+-doped (Na0.47Bi0.47Ba0.06)TiO3 lead-free piezoelectric ceramics

The lead-free piezoelectric ceramics (Na_.47Bi_.47Ba_.06)_1-xCa_xTiO₃ (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca²⁺-doped (Na_.47Bi_.47Ba_.06)TiO₃ ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca²⁺ quantity. A small quantity of Ca²⁺ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca²⁺ content and electric poling. The results demonstrate that the electrical properties of the (Na_.47Bi_.47Ba_.06)TiO₃ lead-free ceramics can be well tuned by varying the Ca²⁺ quantity.     

Synthesis, characterization and optical properties of Mg(OH)2 micro-/nanostructure and its conversion to MgO

Magnesium hydroxide (Mg(OH)₂) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH)₂ with hexagonal crystal structure. An optical band gap of 5.7 eV is determined for Mg(OH)₂ nanodisks from the UV–vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH)₂ nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH)₂ has been converted to MgO by calcination at 450 °C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eV and a broadband PL emission in the UV region. Mg(OH)₂ and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications.     

Microstructure and optical properties of electrodeposited Al-doped ZnO nanosheets

This study grew A1-doped ZnO nanosheets on polycrystalline zinc foils using cathodic electrodeposition in an aqueous solution consisting of 0.02 M Zn(NO₃)₂ and 0.001 M Al(NO₃)₃ at 90 °C. The effects of the electrodepositing potential and thermal annealing on the physical properties of the Al-doped ZnO sheets were investigated. This study observed a high quality sheet-like structure of the electrodeposited Al-doped ZnO for the applied potential larger than −1.1 V, and the sheets were interconnected over the area of interest. The X-ray diffraction patterns showed that the intensity of the Bragg reflections of the electrodeposited Al-doped ZnO sheets increases with the electrodepositing potential because a larger applied potential results in the Al-doped ZnO sheets having a larger lateral dimension and thickness. However, the appearance of the Al-doped ZnO sheets becomes coarse and rough after thermal annealing at 400 °C in ambient air for 4 h. The intensity of the Bragg reflections of the Al-doped ZnO sheets was markedly increased through the thermal annealing due to the improvement of the crystalline quality of the annealed Al-doped ZnO sheets. Annealing caused a large decrease in structural defects of the Al-doped ZnO sheets electrodeposited at −1.3 V causing the sheets to exhibit a sharp photoluminescence peak at ∼380 nm.     

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a₁ and a₂ crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.     

Temperature dependence of macroscopic and microscopic PZT properties studied by thermo-mechanical analysis,dielectric measurements and X-ray diffraction

The main objective of the paper is to point out the influence of composition and of poling state (poled and unpoled samples) on the evolution of various parameters (?_r, dilatation coefficients, lattice parameters) at different scales (lattice, bulk) using X-ray diffraction (XRD), thermo-mechanical analysis (TMA) and dielectric methods. The transition temperatures have been determined from the above measurements and compared. The composition has an influence on the transition temperature and not on the dilatation coefficient value. The poling state influences only the macroscopic dilatation evolution and not the value of the transition temperature. A scale effect is only observed on majoritary tetragonal compositions which show different values of transition temperatures from microscopic and macroscopic methods.     

Hydrothermal synthesis of NaNbO3 with low NaOH concentration

NaNbO₃ fine powders were prepared by reacting niobium pentoxide with low NaOH concentration solution under hydrothermal conditions at 160 °C. The reaction ruptured the corner-sharing of NbO₆ octahedra in the reactant Nb₂O₅, yielding various niobates, and the structure and composition of the niobates depended on the [OH⁻] and reaction time. The fine Nb₂O₅ powder first aggregated to large particles and then turned to metastable intermediates with multifarious morphology. The reaction was fast for the situation of [OH⁻] = 2 M. The [OH⁻] determined the structure of final products, and three types of NaNbO₃ powder with the orthorhombic, tetragonal and cubic symmetries were obtained, respectively, depending on the [OH⁻]. The low [OH⁻] was propitious to yield orthorhombic NaNbO₃. The present work demonstrated that higher [OH⁻] was not favored to synthesize NaNbO₃ powders and the conversion speed in this reaction was not in proportion to the [OH⁻].     

Microwave dielectric properties of multi-ions Ba(Zn,Ta)O3-based perovskite ceramics

In this study, Ba(Zn_1/3Ta_2/3)O₃-based complex perovskite compounds, including Ba(Zn_1/3Ta_2/3)O₃, Ba(Zn_1/3Ta_1/3Nb_1/3)O₃, Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, were prepared and characterized. There was no second phase formation shown in the XRD patterns. Though it has been suggested that substitutions of multiple ions over A-site or B-site of the Ba(Zn_1/3Ta_2/3)O₃ ceramics may not be beneficial to their microwave dielectric properties, the Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramics in this study were found to perform in a fairly acceptable manner. The Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1575 °C for 6 h) and the Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1550 °C for 6 h) reported the following characteristics after annealing at 1400 °C for 10 h: 24.9 and 27.0 for dielectric constants (?_r), 83,000 and 32,100 GHz for quality factors (Q × f) values and −12.8 and −22.6 ppm/°C for temperature coefficients of resonance frequency (τ_f).     

Effects of mechanical-activation and TiO2 addition on the behavior of two-step sintered steatite ceramics

Steatite, as ceramic with composition predominantly resting on magnesium silicate, was produced from economic resources – talc, aluminosilicate clays, and either BaCO₃ or feldspar as flux. Titanium dioxide was a doping agent. Four steatite mixtures were mechanically activated in a planetary ball mill for 30, 45 or 60?min, prior to the thermal treatment. Two-step sintering with initial phase set at 1350?°C and holding period conducted at 1250?°C was applied to initiate diffusion and prevent grain growth. Thereby, a high density ceramic material with low-porous submicron structure was acquired. The effects of TiO₂ addition on densification, microstructure, and dielectric characteristics of steatites were monitored. The thermal stability of green mixtures was tested by differential thermal and thermogravimetric analyses. Changes in crystallinity and mineral phase composition were observed by the X-ray diffraction technique. Microstructural visualization with spatial arrangements of individual chemical elements on surface of the sintered ceramics was acquired by scanning electron microscopy accompanied with EDS mapping. In order to test the possibility of employment of the obtained steatites in insulation materials, electrical measurements were conducted by recording variations of the dielectric constant and loss tangent as a function of alternations in the mix-design and the mechanical activation period.