Narrow Results

Polycrystalline samples of double layered (DL) manganite system La_1.2(Sr_1-xBa_x)_1.8Mn₂O₇(0.0≤×≤0.4) were prepared by the sol-gel method. The anisotropic lattice expansion is observed with the substitution of Ba²⁺ into Sr²⁺ sites. The electrical resistivity and magnetoresistance (MR) measurements were carried out over the temperature range 4.2 K–300 K. The substitution of Ba results in the suppression of T_IM, insulator-to-metal transition temperature. A low temperature upturn of resistivity is seen in all the samples of the system, which is attributed to the spin-glass-like transition. The conduction mechanism above T_IM is explained by Mott variable range hopping (VRH) mechanism. The variation of MR with temperature and applied magnetic field is discussed. From the temperature dependent MR curves, it is observed that the large MR values are present over a wide temperature range and the maximum MR values occur at . The x=0.4 sample exhibits ~31% of MR with the application of a mere 0.4 T field at 5 K, which accounts for ~35% enhancement of MR of parent compound (~23% of MR% at 0.4 T at 5 K). The MR — H data is fitted to the power law ρ = ρ₀-αHⁿ, and it is found that the low temperature MR varies as square root of the applied magnetic field, as expected in conventional metals.

Niobium-substituted BiFeO₃(BiFe_1-xNb_xO₃BFNO) thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by spin coating with a sol–gel technology and rapid thermal annealing. The effects of Nb content (x = 0~0.08) on the microstructure, magnetic and multiferroic properties of thin films were investigated. The result of X-ray diffraction analysis shows that the BFNO thin films have rhombohedral (R3c) to tetragonal (P4mm) phase transition at x = 0.06. The Nb doping in the B-site of BiFeO₃ could induce the appearance of the spontaneous magnetization and polarization by the phase transition of rhombohedral-to-tetragonal. The BFNO thin films with x = 0.06 exhibits the maximum remanent magnetization (2Mr) of 5.2 emu/g.

TiO₂ thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol–gel technique. The influence of annealing temperature on the structural, morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO₂ films has also been examined by optical polaromicrograph (OPM). TiO₂ films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.

The citrate complexing sol–gel process to fabricate lead-free (K,Na)NbO₃ ferroelectric thin films was studied. Soluble niobium source of niobium–citric acid (Nb–CA) solution was utilized as a raw material to synthesize (K,Na)NbO₃ thin films, by pyrolyzing at 450–550${}^{\circ }$C and annealing at 650${}^{\circ }$C. The film pyrolyzed at 450${}^{\circ }$C shows poor crystallization with porous morphology, whereas the film pyrolyzed at 550${}^{\circ }$C appear to be well-crystallized and denser, and the ferroelectricity was also proved by the $P$–$E$ hysteresis loop measurement.

Sm–Co nanoparticles have promising applications in both scientific and industrial fields. In this paper, Sm–Co single-crystal nanoparticles were prepared using respective metal salts and complexing agents, such as citric acid by Pechini-type sol–gel method. The mixture solution was heated to form a highly viscous gel, and then heated at different temperatures to achieve SmCo-oxide. And then Sm–Co particles were yielded by reductive annealing of the precursors. Phase analysis, microstructural investigation and magnetic properties were performed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared (FT-IR) and VSM. TGA trace analysis of the gel determined the heat treatment temperature. XRD results showed that SmCoO₃ and Co₃O₄ were obtained at 800${}^{\circ }$C, FT-IR spectrometry analysis also verified the results. In the calcium-thermal reduction process, Sm₂O₃ and Co were obtained after reductive annealing at 800${}^{\circ }$C, meanwhile Sm–Co nanoparticles were formed at 850${}^{\circ }$C. FESEM analysis revealed that the Sm–Co nanoparticles were composed in the form of spherical granules and exhibited well distribution with size in the range of 100 nm. The room temperature saturation magnetization and coercivity of the Sm–Co nanoparticles were 49.61 emu/g and 3.53 kOe, respectively.

In this work, Sr-substituted samples of single-phase spinel monoferrites with chemical formula ${\mathrm{\text{Ba}}}_{1-x}{\mathrm{\text{Sr}}}_x{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ (x = 0.00, 0.33, 0.67, 1.00) were synthesized using sol–gel auto-combustion method. In order to confirm the single-phase formation of these samples, a sample (x = 0.00) was chosen for heat treatment at different temperatures (100, 300, 400, 600 and $700^{\circ }\mathrm{\text{C}}$) for 4 h. The heat treated sample was then investigated by X-ray diffraction (XRD) analysis and results showed that a single-phase sample can be successfully synthesized at a temperature of $600^{\circ }\mathrm{\text{C}}$, which is much lower than that reported in earlier literature for synthesis of same structured samples. All the synthesized samples were then sintered at $700^{\circ }\mathrm{\text{C}}$ for 4 h to achieve better crystallinity. From XRD patterns, lattice parameters, cell volume and XRD density as a function of Sr-substitution were calculated. Scanning electron microscopy (SEM) results showed that the grain size increased as the temperature was increased. Fourier transform infrared spectroscopy (FTIR) results confirmed the single-phase spinel monoferrites at $700^{\circ }\mathrm{\text{C}}$. From M–H loops (x = 0.0, 0.33, 0.67 and 1.00), different magnetic parameters such as saturation magnetization $(M_s)$, remanance $(M_r)$, coercivity $(H_c)$ and magnetic moment $(n_B)$ were calculated. Magnetocrystalline anisotropy constant and Y–K angles of Sr-doped Ba monoferrites were also calculated. In addition, the variation of different dielectric parameters (real permittivity, imaginary permittivity, real permeability, imaginary permeability, ac conductivity and loss tangent) as a function of frequency (1–6 GHz) has been discussed in this work. The results suggest that the synthesized materials have many advantages over previously reported single-phase spinel monoferrites.

The properties of the cotton fabric with water-repellence finishing by sol method with the hexadecyltrimethoxysilane as additive were observed. The cotton fabrics were immersed in the prepared sols with double dip and double nip dried at 90°C, annealed at 160°C for 3 min. The water repellence and the physical properties such as gas permeability, bending properties, beetling properties, tensile strength, elongation at break, abrasion resistance, and anti-crease properties of the cotton fabrics were investigated. The results showed that anti-crease and tensile strength were improved. However, the abrasion resistance of the cotton fabrics decreased in some way. Both the bending and beetling properties measurement proved that the handle of the treated cotton fabrics changed stiffness. For the dyed fabrics by the water-repellent finishing, the hue was slightly changed, the deeper color was achieved. There is no adverse effect for treated fabric by water-repellent finishing on the fastness.

Y₂SiO₅:Ce³⁺ particles was synthesized by sol–gel process. In all samples treated at 1100°C, monoclinic X₁ phase for all cerium concentration. Luminescence spectra shows broad Ce³⁺ luminescence in Y₂SiO₅ host, which picks around 450 nm. The synthesized and calcined powders were characterized by thermogravimetry-differential scanning calorimeter (TG-DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and photoluminescence spectra (PL).

Nanosized and highly reactive Mg₄Ta₂O₉ were successfully synthesized by aqueous sol–gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg₄Ta₂O₉ was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol–gel process showed great advantages over conventional solid-state method and Mg₄Ta₂O₉ nanopowders with the size of 20–30 nm were obtained at 800°C.

Sintering characteristics and microwave dielectric properties of Mg₄Ta₂O₉–5wt% B₂O₃ ceramics were investigated. With the sintering temperature increasing in the range of 1100${}^{\circ }$C–1350${}^{\circ }$C, the apparent density, ${\epsilon }_r$ and $Q\cdot f$ values increased firstly and then saturated at 1250${}^{\circ }$C with excellent microwave properties: ${\epsilon }_r\sim 12.1$, $Q\cdot f\sim 77,575$GHz and ${\tau }_f\sim -40$ppm/${}^{\circ }$C. Compared to the pure MT ceramics, the B₂O₃ additives effectively decreased the sintering temperature of MT ceramics and had no detrimental effect on the properties of the MT ceramics due to the liquid phase effect.

Microporous silica-alumina thin films were prepared by a simple and robust sol-gel method. Tetraethoxysilane was mixed with an acidic alumina hydrosol. Urea was added for the preparation of the alumina hydrosol, for controlling the polycondensation of the mixed oxide network and also as porogen agent. Thin films were deposited by dip-coating on dense substrates.

IR and ²⁷Al NMR spectroscopic analyses showed that for Si/Al molar ratios up to 6/1, a homogeneous mixed oxide is obtained with a random distribution of Al and Si atoms in the oxide lattice based on tetrahedral units. The deposited layers are crack-free as demonstrated by scanning electron microscopy (SEM) observations. Their microporosity was investigated using ellipsoporosimetry (EP) with films supported on flat substrates.

We synthesized Ba(Ti_1-xZr_x)O₃-based (BTZ) nanopowders modified with Cu and Nb, and sintered ceramics using a one-step sol–gel process. Characterization using TG-DTG, XRD, SEM, and TEM analysis methods revealed that the powders formed at a nanometer scale. The process was controlled by the composition and calcining temperature. BaZrO₃ formed earlier than BaTiO₃ during the calcining, then a Ba(Ti_1-xZr_x)O₃ solid solution formed incompletely, resulting in ceramics with huge permittivity and good temperature stability. Moreover, the maximum dielectric constant (ε_max) first increased and then decreased as the Curie temperature (T_c) shifted to a lower temperature. When the Zr concentration was 5.4 mol%, ε_max was greater than 24,000 and the dielectric loss (25°C) was only 0.005; this meets the Electronic Industries Alliance Y5V specifications. These nanopowders would permit a significant reduction in the thickness of multilayer ceramic capacitors and the huge permittivity of the ceramics will help meet the current demand for device miniaturization in the electronics industry.

(Sr${}_{0.5}$Ba${}_{0.5}$)Nb₂O₆ ultra-fine powders were synthesized by a novel sol–gel route, and the mechanism of the reaction was discussed. SrCO₃, BaCO₃, oxalate niobium and citric acid were used to initiate the sol–gel process, and ethylene glycol (EG) was added to further polymerize the cross-linking structure. The evolution of the (Sr${}_{0.5}$Ba${}_{0.5}$)Nb₂O₆ phase, the reaction process and the microstructures were investigated by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy, DSC-TG and scanning electron microscopy. The synthesis temperature of the (Sr${}_{0.5}$Ba${}_{0.5}$)Nb₂O₆ powders reached as low as 1200${}^{\circ }$C, and the size and morphology of the powders were controlled by temperature. By adjusting the calcination temperature, we obtained (Sr${}_{0.5}$Ba${}_{0.5}$)Nb₂O₆ powders with uniform sizes of 20nm to 500nm. Then, dense (Sr${}_{0.5}$Ba${}_{0.5}$)Nb₂O₆ ceramics were successfully prepared using these ultrafine powders. Finally, an enhanced electrocaloric effect (ECE) value of 0.35${}^{\circ }$C was obtained at 100kV/cm.

Development of novel biomaterials for bone regeneration is based on the sufficient bone-bonding ability, bioactivity and biocompatibility. In this study, novel flexible poly(butylene succinate)/polydimethysiloxane-modified bioactive glass/nano-hydroxyapatite (PBSu/PDMS-BG/nHA) hybrid bioceramic with various nHA concentration on the in vitro bone-like hydroxyapatite (HA) formation, biomineralization activity and osteoblast cell biocompatibility were investigated. The rapid precipitation of HA on the hybrid bioceramic surfaces was found after being immersed in simulated body fluid (SBF) for seven days. Results show that the amount of HA deposition increased with the increase of nHA concentration. The optimized PBSu/PDMS-BG/nHA hybrid bioceramic exhibited good flexibility, high biomineralization activity and good osteoblast cell biocompatibility.

Structural and dielectric properties of Ce-doped ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ powders, with the chemical formulation (Ba${{}_{1-}}_x$${\text{Ce}}_x)$(Ti(${{}_{0.97-}{}_x}_{/4})$- ${\text{Y}}_{0.03})$O₃ such as $x$ = 0%, 1%, 3%, 5%, 7% and 9%, produced by the sol–gel method, have been investigated. X-ray diffraction analysis showed that Ce${}^{3+}$ ions incorporated Ba sites until $x$= 7% indicating that this concentration represents a solubility limit of Ce${}^{3+}$ ions in ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ matrix. Scanning electron microscopy (SEM) analysis showed a decrease in grain size down to the same concentration of 7%. Raman spectroscopy analysis showed the appearance of ${\text{A}}_{1g}$ mode, which we attributed to the effect of incorporation of Ce${}^{3+}$ and Y${}^{3+}$ in BaTiO₃ matrix. Dielectric measurements revealed that doping with cerium lowers the temperature of permittivity maximum at the ferroelectric-to-paraelectric transition (FPT) of the ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ sample, and reaches a value that should be below ${40}^{\circ }$C for $x$= 9%. Moreover, the phenomenon of dielectric resonance was observed on all Ce-doped samples, which was not the case with other dopants as reported in the literature.

In this study, ferroelectric CaBi₄Ti₄O₁₅ (CBT) thin films prepared by sol-gel method and deposited on ITO/glass substrates for applications in system-on-panel (SOP) devices were fabricated and investigated. The electrical and physical characteristics of as-deposited and annealed CBT thin films for metal-ferroelectric-metal (MFM) structures was discussed and investigated. In addition, the ferroelectric properties in annealed CBT thin films on ITO/glass substrate showed and exhibited clear polarization versus electrical field curves. From p-E curves, the 2P_r value and coercive field of annealed CBT thin films were calculated to be 10μC/cm² and 180 kV/cm, respectively. Finally, the maximum capacitance, leakage current density, and transmittance within the ultraviolet-visible (UV–vis) spectrum were also investigated and discussed.

Lithium molybdosilicate (LMS) glasses in different formers compositions, of 20% Li₂O – 80 % [xMoO₃ + (1-x) SiO₂]; where x = 0.1 to 0.5 in steps of 0.1, were synthesized through sol-gel process. Structural characterisations of LMS glasses were made using XRD, FTIR and DSC techniques. XRD pattern of LMS samples showed amorphous phase for gels heat treated to 573 K and further heat treatment above 583 K showed the formation of crystalline multiphases. FTIR spectra for dried LMS gels heated between 338 K – 443 K showed the presence of hydroxyl group on the surface of silicate and molybdoates in the matrix and on further heat treatment, the FTIR spectra revealed the formation of silicate and molybdoate linkages in LMS glassy matrix. DSC curve confirmed the presence of adsorbed water molecules in LMS glassy matrix. Impedance measurements were carried out on LMS samples of different former compositions and the data were analyzed using Boukamp equivalent circuit software. The conductivity was calculated from analyzed impedance data and it is found to be 6.36 × 10^-5 Scm^-1 for x = 0.1 composition of LMS glass.

MoO₃-TiO₂ thin films have been prepared by the sol-gel process. The films were deposited onto alumina substrates with interdigitated electrodes and single crystal silicon substrates using the spin-coating technique. The films were annealed at 400, 450, 500 and 600°C for 1 hour. The energy band gap, morphology and chemical composition of the films have been analyzed using optical, SEM, RBS and XPS techniques. The SEM analysis showed that the films annealed at 500°C are smooth and uniform with nanosized grains and pores. RBS and XPS characterizations have revealed that the films are nearly stoichiometric. Adding TiO₂ to MoO₃ dramatically reduces the resistance of the thin films. The response of the MoO₃-TiO₂ thin films to CO and NO₂ has been investigated at concentrations of 10 to 400 ppm and 0.5 to 10 ppm, respectively. Preliminary results indicate that the films are stable at an operating temperature of 300°C and are sensitive to CO and NO₂. The response and recovery times are approximately one minute. The thin film morphology, chemical composition and its influence on the electrical response of CO and NO₂ gases is discussed in this paper.

The effects of TiO₂ content and heat treatment on the bioactivity and mechanical behavior of polydimethyl-siloxane(PDMS)-modified CaO-SiO₂-TiO₂ hybrid materials were investigated. Samples were prepared by hydrolysis and polycondensation of PDMS, tetraethoxysilane (TEOS), tetraisopropyltitanate (TiPT) and calcium nitrate. The samples with varying (TiPT)/(TEOS + TiPT) molar ratios from 0 to 0.30 were prepared. The apatite-forming ability in a simulated body fluid (SBF) increased with increasing TiO₂ content. The Young’s modulus and strain at failure increased and decreased, respectively, with increasing TiO₂ content. The samples with a fixed molar ratio, (TiPT)/(TEOS + TiPT) = 0.10 were heat-treated at various temperatures from 60 to 300°C for 24 h. The Young’s modulus and failure strain of the heat-treated samples increased and decreased, respectively, with increasing heat treatment temperature, but the bending strength was found to be independent of treatment temperature. Pore- and crack-free trasparent hybrids exhibiting high apatite-forming ability as well as mechanical properties analogous to those of human cancellous bone were developed. These hybrids may be used as a new kind of bioactive bone-reparing materials.