Synthesis and characterization of one-dimensional magnetic photocatalytic CNTs/Fe3O4–ZnO nanohybrids

One dimensional bifunctional magnetic-photocatalytic CNTs/Fe₃O₄–ZnO nanohybrids were synthesized by one-pot polyol sequential process. The as synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectrometer, transmission electronic microscope, energy dispersive spectrometer, physical properties measurement system and UV–Vis absorption spectroscopy. The results exhibit the ZnO forms heterogenerously on the surface of CNTs/Fe₃O₄ and the nanohybrids display superparamagnetic behavior at room temperature. Photocatalytic studies verify the as-prepared sample have high photocatalytic activity toward the photodegradation of methyl orange in solution. In addition, the photocatalyst can be recycled using magnetic field and maintain high photocatalytic activity.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

Study of structural and magnetic properties of (Co–Cu)Fe2O4/PANI composites

The nanocomposites of the polyaniline and Co_1−xCu_xFe₂O₄ (PANI/CoCuFe) were prepared by in-situ oxidative polymerization of aniline. Prepared nanocomposites samples were characterized by using various experimental techniques like X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), Mössbauer spectroscopy and ultraviolet–visible spectrophotometry (UV–VIS). The elemental analysis as obtained from the energy dispersive X-ray spectroscopy (EDAX) measurement is in close agreement with the expected composition from the stoichiometry of the reactant solutions. XRD result confirms that all the samples have the single phase cubic spinel structure. Unit cell parameter ‘a’ is found to decrease with the increase in copper ion substitution. The crystallite size was investigated by using the Debye–Scherer formula and it was found in the range of ∼28–37 nm. FE-SEM confirmed the homogeneous and well defined surface morphology of the synthesized samples. FT-IR study showed the main absorption bands corresponding to the spinel structure those arose due to the tetrahedral and octahedral stretching vibrations. Cation distribution was estimated using XRD data. Hysteresis measurements revealed that the saturation magnetization decreased with increase in Cu²⁺ substitution. Magnetic environment of ⁵⁷Fe in Cu-doped cobalt ferrite was investigated by using Mössbauer spectroscopy. Mössbauer study evidenced the ferrimagnetic behavior of the synthesized samples.     

Synthesis and properties of β-Ga2O3 nanostructures

A novel method was utilized to synthesize one-dimensional β-Ga₂O₃ nanostructures. In this method, β-Ga₂O₃ nanostructures have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Mo films under flowing ammonia in a quartz tube. The as-obtained samples were analyzed in detail using the methods of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) attached to the HRTEM instrument. The results show that the formed nanostructures are single-crystalline Ga₂O₃. The annealing temperature has an evident influence on the morphology of the β-Ga₂O₃ nanostructures. The growth mechanism of the β-Ga₂O₃ nanostructures is also discussed by conventional vapor-solid (VS) mechanism.     

Synthesis,conductivity and dielectric characterization of salicylic acid–Fe3O4 nanocomposite

We report on the synthesis of water dispersible salicylic acid –Fe₃O₄ nanocomposites via a co-precipitation route by using Fe(III) and Fe(II) chloride salts, and salicylic acid. Crystalline phase was identified as Fe₃O₄ and the crystallite size was obtained as 13 ± 6 nm from X-ray line profile fitting. As compared to the particle size of 20 nm obtained from TEM analysis these particles show polycrystalline nature. The capping of salicylic acid around Fe₃O₄ nanoparticles was confirmed by FTIR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface. ac and dc conductivity measurements performed on the nanocomposite revealed semiconductor characteristics and varying trends with temperature due to reorganization of the nanocomposite. Permittivity measurements showed increasing dielectric constant with increasing temperature as expected from semiconductors. Analysis of electrical modulus and dielectric permittivity functions suggest that ionic and polymer segmental motions are strongly coupled in the nanocomposite.     

Crystallization and magnetic properties of a 10Li2O–9MnO2–16Fe2O3–25CaO–5P2O5–35SiO2 glass

The crystallization behavior and magnetic properties of 10Li₂O–9MnO₂–16Fe₂O₃–25CaO–5P₂O₅–35SiO₂ (10LFS) glass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to observe the crystallization behavior and a superconducting quantum interference device (SQUID) for measurements of the magnetic properties. The DTA shows that the 10LFS glass has one broad exothermic peak at approximately 674 °C and one sharp (the highest) exothermic peak at 764 °C. When the 10LFS glass crystallized at 850 °C for 4 h, the crystalline phases identified by XRD were lithium silicate (Li₂SiO₃), β-wollastonite (β-CaSiO₃), lithium orthophosphate (Li₃PO₄), magnetite (FeFe₂O₄) and triphylite (Li(Mn_0.5Fe_0.5)PO₄). The SEM surface analysis revealed that the β-wollastonite and lithium silicate have a lath morphology. The TEM microstructure examination showed that the largest FeFe₂O₃ particles have a size of approximately 0.3 μm. When the 10LFS glass was heat treated at 850 °C for 16 h and a magnetic field of 1000 Oe was applied, a very small remnant magnetic induction of 0.01 emu g⁻¹ and a coercive force of 50 Oe were obtained, which revealed an inverse spinel structure.     

Structural and dielectric properties of Li2O–ZnO–BaO–B2O3–CuO glasses

Glass samples of the system (15Li₂O–30ZnO–10BaO–(45 − x)B₂O₃–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant εφ, loss tan δ, a.c. conductivity, σ_ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration. The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content indicates structural changes of the glass matrix. The glass transition temperature, T _g, and crystallization temperature, T _c, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter (T _c − T _g) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BO₃, BO₄, and ZnO₄. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction.     

Dielectric and magnetic properties of bulk and layered tape cast CoFe2O4–Pb(Fe1/2Ta1/2)O3 composites

The microstructure, dielectric and magnetic properties of bulk and layered CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ composites were studied. Ceramic samples based on previously mixed ferrite and relaxor powders were sintered at 950 °C. Ferrite and relaxor green tapes 150 μm thick were prepared by tape casting, then cut, stacked alternately, laminated and co-sintered at 950 °C. High and broad maxima of dielectric permittivity reaching 2000 at 1 kHz were found for bulk CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ ceramic. Measurements of the magnetization of the investigated composites as a function of magnetic field and temperature exhibited behavior typical of hard magnetic materials. The layered composites showed lower coercivity, higher saturation magnetization and a higher magnetoelectric coefficient than the bulk ceramics. Distinct changes in field- and zero field-cooled magnetization curves at −200 °C could be ascribed to the antiferromagnetic transition of the PFT relaxor phase. Multilayer CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ composites exhibited a magnetoelectric coefficient of 200 mV/(cm Oe) at a frequency of the modulation magnetic field equal to 5 kHz.     

Natural Fe3O4 nanoparticles embedded zinc–tellurite glasses: Polarizability and optical properties

Modifying the optical behavior of zinc–tellurite glass by embedding magnetic nanoparticles has implication in nanophotonics. A series of zinc–tellurite glasses containing natural Fe₃O₄ nanoparticles with composition (80 − x)TeO₂·xFe₃O₄·20ZnO (0 ≤ x ≤ 2) in mol% are synthesized by melt quenching method and their optical properties are investigated using FTIR and UV–vis–NIR spectroscopies. Lorentz–Lorenz relations are exploited to determine the refractive index, molar refraction and electronic polarizability. The sharp absorption peaks of FTIR spectra show a shift from 667 cm⁻¹ to 671 cm⁻¹ in the presence of nanoparticles that increase the non-bridging oxygen, confirmed by the intensity change of the TeO₃ peak at 752 cm⁻¹. A new peak around 461 cm⁻¹ is also observed which is attributed to the band characteristic of covalent Fe–O linkages. A decrease in the Urbach energy as much as 0.122 eV and the optical energy band gap with the increase of Fe₃O₄ concentration (0.5–1.0 mol%) is evidenced. Electronic polarizability of the glasses increases with increasing Fe₃O₄ nanoparticles concentration up to 1 mol%. Interestingly, the polarizability tends to decrease with the further increase of Fe₃O₄ concentration at 2 mol%. The role of magnetic nanoparticles in influencing the structural and optical behavior are examined and understood.     

Sol–gel derived CaO–B2O3–SiO2 glass/CaSiO3 ceramic composites: processing and electrical properties

The CaO–B₂O₃–SiO₂ glass/CaSiO₃ ceramic (CBS/CS) composites were fabricated via sol–gel processing routes. Their densification behavior, structures and dielectric properties were investigated. The precursors of CBS glass and CS ceramic filler were firstly obtained via individual soft chemical route and then mixed together in various proportions. The results indicated that the structures of CBS/CS composites are characteristic of CS and CaB₂O₄ (CB) ceramic phases distributed in the matrix of glass phase at 800–950 °C. The CS ceramic phase not only acts as fillers, but nuclei for the crystallization of CBS glass as well such that the CS content exhibits an effect on the densification and dielectric properties of the composites. The CBS/CS composites with 10% CS sintered at 850 °C own dielectric properties of ε_r < 5 and tanδ = 6.4 × 10⁻⁴ at 1 MHz.     

Synthesis and abrasive properties of nanoparticulate MoO2-modified Al2 ? xFexO3 and Fe2 ? yAlyO3 solid solutions

X-ray diffraction, IR spectroscopy, particle-size analysis, and chemical analysis are used to elucidate the general mechanisms of the formation of nanoparticulate molybdenum-dioxide-modified Al_{2 − x} Fe _x O₃ and Fe_{2 − y} Al _y O₃ solid solutions prepared via heat treatment of ammonium hydroxycarbonate complexes, (NH₄)₂Al₂Fe(OH)₅(CO₃) · nH₂O. The addition of molybdenum dioxide (within 0.005 mol %) is shown to enhance the polishing performance of the oxides for final polishing of nonferrous metals and alloys (copper and brass) by a factor of 6–7 relative to unmodified aluminum iron oxides, which is attributable to the increased chemical activity of the abrasive material. The surface roughness value R _a achieved is below 0.005 μm.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Preparation of polybenzoxazine-functionalized Fe3O4 nanoparticles through in situ Diels–Alder polymerization for high performance magnetic polybenzoxazine/Fe3O4 nanocomposites

Hybrids and nanocomposites of polymer and magnetic Fe₃O₄ nanoparticles have been utilized as magnetically-responsive materials and magnetically-directed nanoparticles. In this work, we prepare polymer-functionalized Fe₃O₄ nanoparticles through in situ Diels–Alder polymerization using maleimide-functionalized Fe₃O₄ nanoparticle as a precursor. Polybenzoxazine-functionalized Fe₃O₄ nanoparticles (MNP-PBz) have been obtained and characterized with Fourier Transform Infrared, X ray photoelectron, and Raman spectroscopies. The high saturation magnetization value of 51.9 emu g⁻¹ of the MNP-PBz nanoparticles demonstrates its superparamagnetism. Moreover, MNP-FBz has been utilized as a nanofiller for preparation of cured PBz/MNP-PBz nanocomposites, which contain various MNP-PBz contents of 67, 50, 33, and 17 wt.%. The sample of PBz/MNP-PBz-67 shows a storage modulus of 8.0 GPa, a saturation magnetization value of 37.6 emu g⁻¹, and a glass transition temperature above 380 °C. As a result, the PBz/MNP-PBz nanocomposites could be classified as magnetically-responsive high performance materials.     

Structure and electrical conductivity relaxation studies of Nb2O5-doped B2O3–Bi2O3–LiF glasses

Glasses with composition (70 − x) B₂O₃·15Bi₂O₃·15LiF·xNb₂O₅ with x = 0–1.0 mol% were prepared by conventional glass-melting technique. The molar volume V _m values decrease and the glass transition temperatures T _g increase with increase of Nb₂O₅ content up to 0.2 mol%, which indicates that Nb⁵⁺ ions act as a glass former. Beyond 0.2 mol% Nb₂O₅ the V _m increases and the T _g decreases, which suggests that Nb⁵⁺ ions act as a glass modifier. The FTIR spectra suggest that Nb⁵⁺ ions are incorporated into the glass network as NbO₆ octahedra, substituting BO₄ groups. The temperature dependence of the dc conductivity follows the Greaves variable range hopping model below 454 K, and follows the small polaron hopping model at temperatures >454 K. σ _dc, σ _ac conductivity and dielectric constant (ε) decrease and activation energy for dc conduction ΔE _dc which increases with increasing Nb₂O₅ content up to 0.2 mol%, whereas σ _dc, σ _ac and (ε) increase and ΔE _dc decreases with increasing Nb₂O₅ content beyond 0.2 mol%. The impedance spectroscopy shows a single semicircle or arcs which indicate only the ionic conduction mechanism. The electric modulus formalism indicates that the conductivity relaxation is occurring at different frequencies exhibit temperature-independent dynamical process. The (FWHM) of the normalized modulus increases with increase in Nb₂O₅ content suggesting that the distribution of relaxation times is associated with the charge carriers Li⁺ or F⁻ ions in the glass network.     

Dielectric properties and microstructure of TiO2 modified (ZnMg)TiO3 microwave ceramics with CaO–B2O3–SiO2

The low-fired (ZnMg)TiO₃–TiO₂ (ZMT–TiO₂) microwave ceramics using low melting point CaO–B₂O₃–SiO₂ as sintering aids have been developed. The influences of Mg substituted fraction on the crystal structure and microwave properties of (Zn_1−x Mg _x )TiO₃ were investigated. The result reveals that the sufficient amount of Mg (x ≥ 0.3) could inhibit the decomposition of ZnTiO₃ effectively, and form the single-phase (ZnMg)TiO₃ at higher sintering temperatures. Due to the compensating effect of rutile TiO₂ (τ_f = 450 ppm/°C), the temperature coefficient of resonant frequency (τ_f) for (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ with biphasic structure was adjusted to near zero value. Further, CaO–B₂O₃–SiO₂ addition could reduce the sintering temperature from 1150 to 950 °C, and significantly improve the sinterability and microwave properties of ZMT–TiO₂ ceramics, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ dielectrics with 1 wt% CaO–B₂O₃–SiO₂ sintered at 950 °C exhibited the optimal microwave properties: ε ≈ 25, Q × f ≈ 47,000 GHz, and τ_f ≈ ± 10 ppm/°C.     

Synthesis and properties of glasses in the K2O–SiO2–Bi2O3–TiO2 system and bismuth titanate (Bi4Ti3O12) nano glass–ceramics thereof

Glasses were prepared by the melt-quench technique in the K₂O–SiO₂–Bi₂O₃–TiO₂ (KSBT) system and crystallized bismuth titanate, BiT (Bi₄Ti₃O₁₂) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and third-order susceptibility (χ³) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ³ with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants (ε_r) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in ε_r in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the glass matrix.     

Synthesis and electrical and magnetic properties of LaSr2Mn2 ? yNiyO7 ? δ solid solutions

LaSr₂Mn_{2 − y} Ni _y O_{7 − δ} layered manganite solid solutions with 0 < y ≤ 0.6 have been prepared by solid-state reactions and sol-gel processing. The synthesis procedure is shown to have a significant effect on the electrical and magnetic properties of LaSr₂Mn_{2 − y} Ni _y O_{7 − δ} ceramics. The highest conductivity is offered by the y = 0.2 material, which is due to partial destruction of Mn³⁺/Mn⁴⁺ charge order. Increasing the degree of nickel substitution on the manganese site influences the ferromagnetic properties of LaSr₂Mn_{2 − y} Ni _y O_{7 − δ} and shifts the magnetoresistance peak to lower temperatures.     

Morphological and magnetic properties of the hydrothermally prepared α-Fe2O3 nanorods

α-Fe₂O₃ nanorods were synthesized via hydrothermal method. X-ray powder diffraction revealed the formation of rhombohedral α-Fe₂O₃ single crystal phase with fiber texture. Scanning and transmission electron micrographs analyses showed that the rhombohedral α-Fe₂O₃ has nanorods in shape with diameters of 40–85 nm and lengths of 150–45,000 nm. Isothermal magnetization vs. applied magnetic field curves measured at room and liquid nitrogen temperatures displayed a variation on magnetic ordering: from weak ferromagnetism at room temperature to not hysteretic behavior at liquid nitrogen temperature that is well described by a Langevin function. Moreover, the zero field cooling-field cooling curves under applied magnetic field of 100 Oe confirms the decreasing of Morin temperature transition due to nanometric size of the samples.