Narrow Results

The Ni${}_{1-x}$Co_xTiO₃$(0\le x\le 1)$ solid solution powders were prepared by an aqueous sol–gel method. The structural, optical, magnetic and ferroelectric properties of NiTiO₃ were investigated by X-ray diffraction, scanning electron microscope, UV–Vis absorption, vibration samples magnetometer and ferroelectric test system. The X-ray diffraction analysis revealed that prepared materials were in a single phase with rhombohedral structure with $x$ up to 1. The increasing Co content resulted in decreasing of tolerance factor and increasing of the lattice constant. The crystalline size increased with an increase of Co content. The optical bandgap value of solid solution increased from 2.23eV for NiTiO₃ to 2.36eV for CoTiO₃. The magnetic hysteresis loop results indicate that all samples showed paramagnetic state at room temperature. A correlation between magnetization values and composition of the materials was observed with magnetization values which increased with increasing of CoTiO₃ content in solid solution. Ferroelectric polarization analysis showed that the polarization of the Ni${}_{1-x}$Co_xTiO₃ solid solution depended on x value and reached the maximum with $x=0.4$.

In this paper, Eu³⁺-doped CaTiO₃ (CTO) nanoparticles were prepared by a sol-gel method. Three different charge compensation mechanisms were realized by substituting Eu ion at different sites. (i) Ca site substitution with Ca vacancy compensation (CTO-A); (ii) Ti site substitution with O vacancy compensation (CTO-B); (iii) simultaneous substitution at both Ca and Ti sites with self-compensation (CTO-AB). Strongly related to the site substitution, the photoluminescent (PL) intensities were increasing in the sequence of CTO-B > CTO-AB > CTO-A. The absorbance spectra analysis of pure CTO nanoparticles showed absorption in the UV light region, while the absorption of Eu-doped CTO samples exhibited the blue shift owing to the presence of Eu³⁺. Moreover, the photocatalytic activities of samples for decomposing dyes were reverse to the sequence of PL intensities. The PL properties and photocatalytic activity of the Eu³⁺-doped CTO nanoparticles were thus discussed in detail from the viewpoints of the microstructures and charge transfer-related processes.

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x%Ce₂O₃ + y%La₂O₃ + z%Y₂O₃ compounds (named BNT–BT– x/y/z) were synthesized by a sol–gel technique, for (x,y,z) = (0,0,0), (0.25, 0.25, 0.25), (0.25, 0.5, 0.5), (0.5, 0.25, 0.25) and (0.5, 0.5, 0.25). The structural variation according to the different system compositions is investigated by X-ray diffraction analyses. The results shows that the addition of Ce₂O₃, La₂O₃ or Y₂O₃ in BNT–BT system, do not modify the crystalline structure, and a rhombohedral–tetragonal morphotropic phase boundary is maintained for different dopant addition. The BNT–BT–x/y/z-based ceramics sintered at relatively low temperature (1100°C) exhibit a good densification ratio. The optimum dielectric and piezoelectric properties are obtained with the BNT–BT–0.5/0.25/0.25 composition. High dielectric properties at room temperature (ε_r > 1000) and low dielectric losses (tan δ < 4 × 10^-2) are obtained for this composition. This compound exhibits a piezoelectric constant d₃₃ of 95 pC/N, a good polarization behavior is observed with high remanent polarization P_r of 9.21 μC/cm² and low value coercitive field E_c of 2.66 kV/mm.

Dielectric behavior of aluminum oxide (Al₂O₃) thin film under high DC electric field is presented and discussed. Aluminum oxide thin films were prepared starting from aluminum isopropoxide as a precursor via a wet chemistry route. Silicon substrates and silica glass substrates were used to deposit the films via spin-coating technique. The deposited films were then annealed under 450°C–700°C for 2–3 h. Dense, crack-free and uniform films were obtained. The thickness of the films is in the range of 200–800 nm. The films obtained are in amorphous state as revealed by the X-ray diffraction patterns. Voltage–Current (V–I) characteristics of the films were used to study the dielectric behavior of the films. Very low leakage current density J under high DC electric field E can be obtained. The breakdown electric field of the films is around 1.2 MV/cm. The V–I characteristics of the films are slightly nonlinear. With platinum as bottom electrode and gold as top electrode, successive breakdown phenomena of the films under high DC electric field were observed. Each breakdown event of the film corresponds to a sharp spike at the V–I plot of the sample. The shape of the breakdown spots of the films are in crater-like with a breakdown channel of diameter around a few micrometers as revealed by SEM images. The top gold electrode at the breakdown spots either splashed out or ripped off from the breakdown spots, which isolated the breakdown spots from rest of the electrode, and made the successive breakdown of the sample possible. The breakdown spots of the sample are concentrated at the edge of the electrode with proportional spacing, which can be easily understood as the edge effect of the parallel capacitor configuration, while the uniform distribution of the breakdown spots signifies that the uniformity of the films thus prepared are satisfied. Breakdown spots apart from the electrode edge can also be observed. Most of such spots associated with ripped-off gold film electrode in large area. We suppose such breakdown took place at higher electric field after the successive breakdown at the electrode edge and the isolation of the edge part from rest of the sample. Higher energy is needed to tear off larger section of the electrode. The breakdown characteristics of the films reported in this work are useful for the further study to enhance the breakdown strength of the film.

The influence of temperature on the dielectric properties of sol-gel routed spin-coated molybdenum trioxide (MoO${}_3)$ thin film has been investigated. Prepared films were annealed at temperatures 250${}^{\circ }$C, 350${}^{\circ }$C and 400${}^{\circ }$C. The phase transformation from amorphous to $\alpha$-orthorhombic phase with preferential orientation (0 2 2) has been found by XRD for the film annealed above 250${}^{\circ }$C. The vibration modes of $\alpha$-orthorhombic MoO₃ have been examined by Raman spectrum. The predominant Raman’s band of $\alpha$-orthorhombic MoO₃ thin film has been found at the frequency range 1000–600cm${}^{-1}$. Using the UV–Vis spectrum, the band gap of the film is found to be 3.3–3.8eV. The surface morphology of the MoO₃ films has been examined by scanning electron microscope. The AC conductivity measurement of the MoO₃ film has been carried out in the frequency range 10–10⁶ Hz. The frequency dependence of the impedance has been plotted in the complex plane. The variation of the capacitance and dielectric constant of MoO₃ film with respect to temperature and frequency has been analyzed. Tunability of capacitance and figure of merit of the film are also determined.

The nanostructured titanium dioxide (TiO${}_2)$ thin films have been prepared for the molar concentrations of titanium tetra isopropoxide (TTIP) 0.05M, 0.1M, 0.15M and 0.2M by sol–gel routed spin coating technique with calcination at 450${}^{\circ }$C. The processing parameters such as, pH value (8), catalyst HCl (0.1ml), spin speed (3000rpm) and calcination temperature (450${}^{\circ }$C) are optimized. The crystalline nature and surface morphology were analyzed by XRD, SEM and AFM analysis. The XRD results confirm that the films are crystalline with anatase phase, and are nanostructured. The SEM micrographs of the TiO₂ film reveal the spherical nature of the particle. AFM analysis establishes that the uniformity of the TiO₂ thin film was optimized at 0.2M. The optical measurements show that the transmittance depends on the molarity, and the optical band gap energy of TiO₂ films is found to be inversely proportional to molarity. The I–V characteristics exhibit that the molarity strongly influences the electrical conductivity of the film. The results indicate that the significant effect of molarity on structural, optical and electrical properties of the nanostructured TiO₂ thin films will be useful to photovoltaic application.

Zinc substituted cobalt ferrite nanoparticles with elemental composition Co${}_{1-x}$Zn_xFe₂O₄ ($x=0.0$, 0.2, 0.4, 0.6) were prepared by the sol-gel auto-combustion technique using Co, Fe, Zn nitrate as a precursor where nitrates to citrate was 1:3. The as prepared powder of cobalt zinc ferrite was sintered at 900^∘C for 3h. Structural, morphological, dielectric and magnetic properties were studied by x-ray diffractometer (XRD), scanning electron microscope (SEM), high precision impedance analyzer and vibrating sample magnetometer (VSM), respectively. The peaks obtained from the XRD confirmed samples having crystallite ($\sim$32–36nm) single phase inverse spinel structure without any traceable impurity. Lattice parameters were calculated from XRD and it increases with Zn content. SEM revealed irregularly shaped grains ($\sim 0.5$–0.7$\mu$m) morphology with heterogeneous distribution. The dielectric constant (${\epsilon }^{\prime }$) and dielectric loss ($tan\delta$), have been measured as a function of frequency at room temperature. The dependence of ${\epsilon }^{\prime }$ and $tan\delta$ with frequency showed the normal dielectric behavior in accordance with the Maxwell-Wagner type of interfacial polarization and electron hopping change between Co${}^{2+}$ and Co${}^{3+}$ as well as between Fe${}^{2+}$ and Fe${}^{3+}$ ions at octahedral sites.

Polycrystalline NiCuZn ferrite (Ni_xCu${}_{0.3}$Zn${}_{0.7-x}$Fe₂O₄; $x=0.2$, 0.3, 0.4 and 0.5) were prepared through sol–gel auto combustion method applying double sintering technique. Structural, morphological, elemental analyses (EDS), Fourier-transform infrared spectroscopy (FTIR), Direct Current (DC) electrical resistivity, dielectric, magnetic and optical properties of prepared samples were analyzed. XRD profiles reveal the formation of simple cubic spinel structure without any traceable impurity. The average crystallite size lies within the range of 22–29nm. Lattice parameter decreases with increasing Ni concentration. Room temperature DC resistivity was recorded from $6.39\times 10^5$ to $3.79\times 10^5$$\mathrm{\Omega }$cm. Both dielectric constant ($\dot{\epsilon }$) and loss factor (tan$\delta$) were decreased with increase of frequency while AC conductivity increases. FTIR absorption peak occurred at three different frequency ranges at 570–577cm${}^{-1}$, 1635–1662cm${}^{-1}$ and 3439–3448cm${}^{-1}$. Magnetic properties were investigated by using vibrating sample magnetometer (VSM). Decreasing trends were observed for saturation magnetization ($M_s$), magnetic coercivity ($H_c$) and remanant magnetization ($M_r$) with the increase of Ni content. Optical band gap ($\sim$2.70–2.79eV) were calculated from diffuse reflectance data by using Kubelka–Munk function.

Sol–gel technology was applied to fabricate Eu-doped BaTiO₃/SiO₂ multilayer structures by spinning on silicon and fused silica substrates. Eu photoluminescence (PL) was investigated depending on the annealing temperature of these structures. The samples demonstrate the room temperature luminescence corresponding to ⁵${\text{D}}_0\to {}^7$F_J ($J=1$, 2, 3, 4) transitions of trivalent europium with the most intensive band at 615 nm. For the structure on fused silica with Eu in the BaTiO₃ cavity, increase of the annealing temperature from $450^{\circ }$C to $700^{\circ }$C results in modification of the luminescence indicatrix and lowering of the luminescence intensity in the direction along the surface normal. For BaTiO₃/SiO₂ multilayer structure generated on silicon, scanning electron microscopy (SEM) analyses reveal disordering after annealing at $1000^{\circ }$C. This heat treatment provides also an increase of the Eu luminescence intensity.

Erbium-doped barium titanate (BaTiO₃:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate (${\text{SrTiO}}_3)$ xerogel film on Si substrate after annealing at 800${}^{\circ }$C or 900${}^{\circ }$C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to ²${\text{H}}_{11/2}\to$⁴${\text{I}}_{15/2}$, ⁴${\text{S}}_{3/2}{\to }^4$${\text{I}}_{15/2}$, ⁴${\text{F}}_{9/2}{\to }^4$${\text{I}}_{15/2}$ and ⁴${\text{I}}_{9/2}\to$⁴${\text{I}}_{15/2}$ transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO₃:Er\porous SrTiO₃\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.

Lead-free (${\text{K}}_{0.5}$${\text{Na}}_{0.5}$)NbO₃ (KNN) and ${\text{Li}}_{0.06}$(${\text{K}}_{0.5}$${\text{Na}}_{0.5}$)${}_{0.94}$NbO₃ (LKNN) thin films were fabricated by a sol-gel method. The effects of Li substitution on crystal structure, microstructure and electrical properties of KNN film were systematically studied. Li doping can enhance the ferroelectric and piezoelectric properties of KNN film. Compared with pure KNN film, the LKNN film possesses larger remanent polarization ($P_r$$\sim$ 9.3 $\mu$C/${\mathrm{\text{cm}}}^2$) and saturated polarization ($P_s$$\sim$ 41.2 $\mu$C/${\mathrm{\text{cm}}}^2$) and lower leakage current density ($\sim {10}^{-5}$A/${\mathrm{\text{cm}}}^2$ at 200 kV/cm). Meanwhile, a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient ($d_{33}$$\sim$ 105 pm/V). Excellent fatigue resistance ($\sim$${10}^9$ switching cycles) and aging resistance ($\sim$ 180 days) demonstrate the long-term working stability of LKNN film. These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems (MEMS).

Ba_0.7Sr_0.3TiO₃ was prepared via simple sol-gel method by using titanium tetrabutoxide, barium and strontium carbonates, citric acid and ethylene glycol as starting materials. Simultaneous Thermal Analysis (STA) was used to examine thermal behavior of xerogel. The crystallite size of BST was about 21nm calculated by X-Ray diffraction (XRD) and confirmed by transition electron microscopy (TEM). Using these nanocrystalline powders, BST pellets were prepared and sintered in various temperatures. The grain size effect on electrical properties was studied and found that as the grain size decreased, the dielectric constant decreased too.

Titanium diboride (TiB₂) has attracted great interests for its excellent mechanical properties, chemical resistance and good thermal and electrical conductivities. So it is widely applied as cutting tool composites, wear resistant parts, metal melting crucibles and electrode materials. This paper presents synthesis of nano titanium diboride powders via sol-gel method using a mixture of TTIP and B₄C as precursors. In the hydrolysis step, B₄C to TTIP molar ratio varied from 1.3 to 2.5. Solution samples stirred well and after aging and drying process, they were heat treated in an argon atmosphere. X-ray diffraction (XRD) patterns and Scanning electron microscopy (SEM) analysis showed that the percentage of synthesized TiB₂ increased gradually as the molar ratio of B₄C to TTIP reached to 2.3, afterward increasing the B₄C to TTIP molar ratio caused decreasing of titanium diboride percentage.

Nanostructured hybrid silica/epoxy films containing boehmite nanoparticles were investigated in the present work as pretreatments for AA2024 alloy. To produce the nanocomposite sol-gel films, boehmite nanoparticles prepared from hydrolysis/condensation of aluminum isopropoxide (AlI) were doped into another hybrid organosiloxane sol. The produced oxide nanoparticles have the capability to act as nanoreservoirs of corrosion inhibitors, releasing them controllably to protect the metallic substrate from corrosion. For this purpose the corrosion inhibitor, cerium nitrate, was introduced into the sol-gel system via loading the nanoparticles. The morphology and the structure of the hybrid sol-gel films were studied by Scanning Electron Microscopy (SEM). The corrosion protection properties of the films were investigated by Potentiodynamic Scanning (PDS) and Electrochemical Impedance Spectroscopy (EIS). The results show that the presence of boehmite nanoparticles highly improved the corrosion protection performance of the silica/epoxy coatings. Moreover, they can act as nanoreservoirs of corrosion inhibitors and provide prolonged release of cerium ions, offering a self-healing property to the film.

The particles of TiO₂ core/ SnO₂ shell nanocomposite were prepared by hydrolysis of SnCl₄.5H₂O in the presence of titania nanoparticle after drying and calcinations treatments. TiO₂ particle were produced from titanium isopropoxide sol by hydrothermal processing. X-ray diffraction (XRD), Fourier transformed infrared (FTIR), and transmission electron microscopy (TEM) were used to characterize the TiO₂/ SnO₂ core shell nanocomposites. The obtained results from XRD show that the SnO₂ nanoparticles coated on TiO₂ yields diffraction peaks correspond to the crystalline SnO₂ phase. Also, TEM results show that the nanocomposite particles have a spherical morphology and a narrow size distribution. The thickness of SnO₂ shell on the surface of TiO₂ particles were about 8 nm. Moreover, the results obtained from EDX analysis show that the core-shell structured nanocomposites have crystalline structure.

One of the most important objectives in the field of biomaterials science and engineering is development of new materials as bone substitutes. Silica (SiO₂) has an important role in the biomineralization and biological responses. The aim of this research was to prepare and characterize hydroxyapatite-silica (HA-SiO₂) composite nanopowder with different content of silica. Hydroxyapatite-silica composite nanopowders with 20 and 40 wt% silica were prepared using a sol–gel method at 600°C with phosphoric pentoxide and calcium nitrate tetrahydrate as a source of hydroxyapatite; also, tetraethylorthosilicate and methyltriethoxisilane as a source of silica. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques were used for characterization and evaluation of the products. The results indicated the presence of nanocrystalline hydroxyapatite phase beside amorphous silica phase in prepared composite nanopowders. Moreover, by increasing the content of silica in composite nanopowders, the crystallinity will be decreased,and the ability of the product as a bone substitute material might be controlled by changing the content of the ingredients and subsequently its structure.

TiO₂ thin films were deposited on glass substrates by sol-gel method. Nanocrystalline TiO₂ thin films were prepared at ambient conditions and titanium tetraisopropoxide [C₁₂H₂₈O₄Ti] was used as a Ti-precursor. The effect of annealing temperature on optical properties of nanocrystalline TiO₂ thin films was studied. The as-deposited films were dried at 100 °C for 1 hr. The films formed were further heated in temperature between 200 and 500 °C for 1 hr. The films were characterized by different techniques: XRD, UV-visible spectroscopy, FTIR spectroscopy and FESEM. The characterization studies revealed that the films are crystallized as anatase phase and nano-structured with better optical properties α = 0.89 as compared to reported data. The optical measurement showed the indirect band gap between 3.31 and 3.35 eV with corresponding crystallite sizes between 8.9 and 3.7 nm. The FESEM image of film annealed at 400 °C showed spherical nanocrystalline structure of TiO₂ particles. The crystallite sizes obtained from FESEM image are found to be between 30 and 100 nm. It is also observed that refractive index of the film increases with increasing the annealing temperature. The smaller crystallite size gives larger band gap due to quantum size effects.

We report a novel synthesis technique of ceria nanoparticles by a sol-gel type chemical process using poly-vinyl alcohol (PVA) as a capping as well as a reducing agent. The as-synthesized CeO₂ nanoparticles were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The XRD analysis reveals the fluorite type face centered cubic structure in the ceria nanoparticles with an average crystallite size of 6 nm and 9 nm for the samples calcined at 350°C and 400°C, respectively.

The structural and magnetic measurements have been carried out on La_0.67Sr_0.33Mn_0.93Zn_0.07O₃ (LSMZO) polycrystalline sample. The sample has been prepared through Sol-Gel route. X-ray diffraction (XRD) pattern confirms the single phase nature of the sample with orthorhombic crystal symmetry. Field dependent magnetization shows the hysteresis loop with very low coercive field and the magnetization does not saturate up to the field of 5000 gauss in magnitude.

Dielectric behaviour of Nanocrystalline CaFe₂O₄ ferrite synthesized by advanced sol- gel method has been investigated as a function of frequency at different temperatures. Rietveld profile refinement of the XRD pattern confirms formation of cubic spinel structure of the specimen.The dispersion in dielectric behavior of CaFe₂O₄ferrite sample has been observed in the temperature range of 100-250˚C as a function of frequency in the range 75 kHz to 10 MHz Both the real value of dielectric constant (ɛ′) and the dielectric loss factor (tanδ) decrease with frequency. This decrease in the values of ɛ′ and tanδ could be explained on the basis of available ferrous, i.e. Fe²⁺, ions on octahedral sites such that beyond a certain frequency of applied electric field the electronic exchange between the ferrous and ferric ions i.e. Fe²⁺↔Fe³⁺ cannot follow the applied alternating electric field.