Synthesis, Structural and Optical Characterization of Sol–Gel-Derived Y-Doped Mesoporous CeO2

Highly crystalline and thermally stable undoped CeO₂ and Y-doped mesoporous CeO₂ particles have been synthesized from cerium(III) nitrate hexahydrate [Ce(NO₃)₃·6H₂O] by the sol–gel method. Mesoporous CeO₂ doped with 2 mol.% Y₂O₃ and calcined at 500°C possesses specific surface area of 130.39 m²/g and retains a surface area of 91.84 m²/g at 600°C. In comparison, undoped calcined materials have smaller specific surface areas of 43.23 m²/g and 20.24 m²/g at 500°C and 600°C, respectively. Results from x-ray diffraction (XRD) analysis, Raman spectroscopy, and selected-area electron diffraction (SAED) analysis indicated that the synthesized undoped CeO₂ and Y-doped mesoporous CeO₂ have the fluorite structure of bulk CeO₂. The crystallite size of CeO₂ is also considerably reduced by doping. The optical bandgap was found to be 3.24 eV for the undoped and 3.36 eV for the doped samples with calcination at 600°C. These results suggest that there are potential applications of Y-doped mesoporous CeO₂ with nanocrystals in the design of photocatalysts and optical devices.     

Tuning the Properties of CZTS Films by Controlling the Process Parameters in Cost-Effective Non-vacuum Technique

Highly dispersive Cu₂ZnSnS₄ (CZTS) nanoparticles were successfully synthesized by a simple solvothermal route. A low cost, non-vacuum method was used to deposit CZTS nanoparticle ink on glass substrates by a doctor blade process followed by selenization in a tube furnace to form Cu₂ZnSn (S,Se)₄ (CZTSSe) layers. Different selenization conditions and particle concentrations were considered in order to improve the crystallinity and surface morphology; the annealing temperature was varied between 400°C and 550°C and the annealing time was varied between 5 min and 20 min in a selenium-nitrogen atmosphere. The influence of annealing conditions on structural, compositional, optical and electrical properties of CZTSSe thin films was studied. An improvement in the structural and surface morphology was observed with increasing of annealing temperature (up to 500°C). An enhancement in the crystallinity and surface morphology were observed for thin films annealed for 10–15 min. Absorption study revealed that the band gap energy of as-deposited CZTS thin film was approximately 1.43 eV, while for CZTSSe thin films it ranged from 1.15 eV to 1.34 eV at different annealing temperatures, and from 1.33 eV to 1.38 eV for different annealing times.     

Photochemical Deposition of Highly Dispersed Pt Nanoparticles on Porous CeO2 Nanofibers for the Water‐Gas Shift Reaction

Ceria (CeO₂) nanofibers with high porosity are fabricated using an approach involving sol–gel, electrospinning, and calcination. Specifically, cerium(III) acetylacetonate and polyacrylonitrile (PAN) are dissolved in N,N‐dimethylformamide (DMF) and then electrospun into nanofibers. The PAN matrix plays a critical role in stabilizing the porous structure from collapse during calcination in air up to 800 °C. CeO₂ porous nanofibers comprising an interconnected network of single crystalline and fully oxidized CeO₂ nanoparticles about 40 nm in size are obtained. The hierarchically porous structure of the CeO₂ nanofibers enables the facile deposition of Pt nanoparticles via heterogeneous nucleation in a photochemical method. When conducted in the presence of poly(vinyl pyrrolidone) (PVP) and 4‐benzyolbenzoic acid, uniform Pt nanoparticles with an average diameter of 1.7 nm are obtained, which are evenly dispersed across the entire surface of each CeO₂ nanofiber. The high porosity of CeO₂ nanofibers and the uniform distribution of Pt nanoparticles greatly improve the activity and stability of this catalytic system toward the water‐gas shift reaction. It is believed that this method could be extended to produce a variety of catalysts and systems sought for various industrial applications.     

Effects of Laser Excitation and Temperature on Ag/GaSe0.5S0.5/C Microwave Filters

The effects of temperature, illumination, and microwave signals on Ag/GaS_0.5S_0.5/C Schottky-type microwave filters have been investigated. The devices, which were produced from thin layers of GaSe_0.5S_0.5 single crystal, had room temperature barrier height and ideality factor of 0.65 eV and 3.28, respectively. Barrier height increased uniformly with increasing temperature, at 2.12 × 10^?2 eV/K, and the ideality factor approached ideality. The devices can even function at 95°C. A current switching phenomenon from low to high injection (“On/Off”) was also observed; this current switching appears at a particular voltage, V _s, that shifts toward lower values as the temperature is increased. When the devices were reverse-biased and illuminated with a laser beam of wavelength 406 nm, a readily distinguishable V _s was observed that shifted with increasing laser power. When the devices were run in passive mode and excited with an ac signal of power 0.0–20.0 dBm and frequency 0.05–3.0 GHz they behaved as band filters that reject signals at 1.69 GHz. Device resistance was more sensitive to signal amplitude at low frequencies (50 MHz) than at high frequencies. The features of these Ag/GaS_0.5S_0.5/C Schottky devices imply that they may be used as optical switches, as self standing, low band-pass, band reject filters, and as high band-pass microwave filters.     

Synthesis of Size-Controlled SrFe12O19 Using Modified Spray Pyrolysis–Calcination Method and Their Magnetic Properties

Strontium hexaferrite (SrFe₁₂O₁₉, SrM) suitable for high-performance permanent magnet applications was synthesized by salt-assisted ultrasonic spray pyrolysis (SA-USP) and subsequent calcination. To control the particle size, the intermediate phase of SrM was collected by SA-USP and various sizes of SrM were obtained by calcining the as-prepared sample at temperatures ranging from 800°C to 1050°C. The synthesized SrM was magnetically aligned by using an external magnetic field to improve remanence. The synthesized particles were of nano- to submicron scale and nonagglomerated. The magnetic properties and squareness of the material depended on the particle size and distribution. Additionally, the NaCl added during synthesis facilitated the formation of nonagglomerated particles, while enhancing and controlling particle growth. The optimum magnetic properties were achieved at calcination temperature of 1000°C, resulting in coercivity of 5646 Oe, saturation magnetization of 73.3 emu/g, and remanence of 59.1 emu/g (80.6% of M _s).     

Effect of calcination temperature on Cu doped NiO nanoparticles prepared via wet-chemical method: Structural,optical and morphological studies

In the present study, NiO and Cu-doped NiO nanoparticles were successfully synthesized by wet chemical method at room temperature using sodium hydroxide (NaOH) as precipitating agent. The as-prepared Cu-doped NiO powder samples were subjected to three different calcination temperatures such as, 350 °C, 450 °C and 550 °C in order to investigate the impact of calcined temperatures on the phase formation, particle size and band gap evolution. The phase formation and crystal structure information of the prepared nanomaterials were examined by X-ray powder diffraction (XRD). XRD revealed the face-centered cubic (FCC) structure. Average crystalline size of pure and doped samples estimated using Scherer formula was found to be 15 nm and 9 nm respectively. With increase in the calcination temperature from 350 °C to 550 °C for the Cu doped NiO samples the particle size of the nanoparticles was found to increase from 4 nm to 9 nm respectively. The optical study for both pure and doped NiO nanoparticles was performed using an UV–Vis spectrophotometer in the wavelength range of 200–800 nm. The strong absorption in the UV region confirms the band gap absorption in NiO and was estimated from the UV–Vis diffuse reflectance spectra via Tauc plot. Systematic studies were also carried out to study the effect of calcination on the optical transmittance. Samples were also investigated using Raman and Fourier Transform Infrared Spectroscopy (FTIR). Furthermore, morphology of the pure NiO and Cu-doped NiO Nanoparticles were examined by scanning electron microscope (SEM).     

Sol–Gel Grown SnO<Subscript>2</Subscript> Nanoparticles: Evaluation of Structure,Morphology, and Raman Spectra

Tin oxide (SnO₂) nanoparticles (TONPs) were prepared using sol–gel method under different growth conditions. The influence of calcination temperature (450°C and 600°C) and molecular weight of polyethylene glycol (PEG 300 and PEG 4000) on the nanocrystallinity, surface morphology, and Raman spectra of as-prepared TONPs were evaluated. Variation of calcination temperature and dopant (sulfosuccinic acid, SA) was found to affect considerably the structure, surface morphology, and Raman activities of the TONPs. The size of TONPs estimated using Scherrer equation was discerned to be in the range of 15–32 nm. The observed intensity enhancement in the Raman vibrational modes at lower calcination temperature was attributed to the enlargement of TONPs size. The absorption of molecules at the TONPs surface led to a quenching in the A ₂ g and Eu Raman peaks. Raman peaks centered around 673 cm^?1, 799 cm^?1, 640 cm^?1 , and 432 cm^?1 corresponding to A1g, B2g, A1g, and Eg modes, respectively have manifested highest peaks intensity. Furthermore, the enhancement of the Eg mode due to the addition of SA dopant was ascribed to the Jahn–Teller distortion mechanism.     

Thermally induced structural changes and optical properties of tin dioxide nanoparticles synthesized by a conventional precipitation method

Tin dioxide (SnO₂) nanoparticles were synthesized by a conventional precipitation method using the reaction between tin chloride pentahydrate and ammonia solutions. The obtained powders were calcined at varied temperatures from 300 to 1050 °C, and then characterized by using thermogravimetric analysis, differential thermal analysis and Fourier transformation infrared spectroscopy. The average crystallite size, determined by x-ray diffraction, was found to be in the range of 3.45–23.5 nm. The analysis exhibited a tetragonal phase. The activation energy of crystal growth was calculated and found to be 12.12 kJ/mol. The microstructure of nanoparticles was examined by high resolution transmission electron microscopy. Optical properties were investigated by a UV–vis absorption spectrophotometer. The calculated optical band gap lies between 4.75–4.25 eV as a result of increasing the calcination temperatures and crystallite size.     

Structure and electrical properties of polycrystalline SiGe films grown by molecular beam deposition

The structural and electrical properties of polycrystalline Si_0.5Ge_0.5 films 150 nm thick grown by molecular beam deposition at temperatures of 200–550°C on silicon substrates coated with amorphous layers of silicon oxynitride were studied. It is shown that the films consist of a mixture of amorphous and polycrystalline phases. The amorphous phase fraction decreases from ～50% in films deposited at 200°C to zero in films grown at 550°C. Subsequent 1-h annealing at a temperature of 550°C results in complete solid-phase crystallization of all films. The electron transport of charge carriers in polycrystalline films occurs by the thermally activated mechanism associated with the energy barrier of ～0.2 eV at grain boundaries. Barrier lowering upon additional annealing of SiGe films correlates with an increase in the average grain size.     

Synthesis based structural and optical behavior of anatase TiO2 nanoparticles

The effect of synthesis method on optical and photoconducting properties of titanium dioxide (TiO₂) nanoparticles has been investigated. Sol–gel and co-precipitation methods have been employed to prepare pure anatase phased TiO₂ nanoparticles calcinated at different temperatures below 500 °C. The optimized value of average crystallite size is within the range of 19−21 nm for a common calcination temperature of 400 °C for both the methods. The redshift in optical band gap of 0.9 eV has been observed for the sample synthesized by co-precipitation method with respect to the sol–gel method. The photoluminescence spectrum exhibits broad visible emission in both routes of synthesis while photoconductivity shows fast growth and decay of photocurrent in TiO₂ prepared by co-precipitation method as compared to TiO₂ prepared by the sol–gel method under visible illumination. Crystal structure based Rietveld refinement of X-ray diffraction data, scanning electron microscopy as well as photoluminescence and photoconductivity measurements were performed to characterize nanocrystalline anatase TiO₂.     

Dielectric Properties and Defect Chemistry of WO3-Doped K0.5Na0.5NbO3 Ceramics

The dielectric properties and conductivity behavior of WO₃-doped K_0.5Na_0.5 NbO₃ ceramics were investigated as a function of temperature (25°C to 600°C) and frequency (40 Hz to 10⁶ Hz). The dielectric loss and direct-current (DC) conductivity of the ceramics depend strongly on the tungsten content. A high-temperature dielectric relaxation near temperature of 500°C was observed and analyzed using the semiempirical complex Cole–Cole equation. The activation energy of the dielectric relaxation was estimated to be ～2 eV and increased with increasing WO₃. The frequency-dependent conductivity can be well described by the universal dielectric response law. The activation energy obtained from the DC conductivity changes from 0.93 eV to 1.49 eV. A possible mechanism for the high-temperature dielectric relaxation and conductivity is proposed based on the activation energy value and defect compensation.     

The Role of the Nickel Catalyst and Its Chemical and Structural Evolution During Carbon Nanopearl Growth

The role of the nickel catalyst size and its chemical and structural evolution during the early stages of carbon nanopearl nucleation and growth, by chemical vapor deposition from acetylene/argon mixture, were investigated and correlated with the resulting nanopearls’ morphological and structural properties. Carbon nanopearls were grown using Ni nanoparticles that were 20 nm and 100 nm in size, at a growth temperature of 850°C, for the following growth times: 10 s, 30 s, 60 s, 90 s, 120 s, and 300 s. x-Ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy were performed on the carbon nanopearl samples. The x-ray diffraction and x-ray photoelectron spectra showed that the following chemical constituents were present during the growth of carbon nanopearls: NiO, Ni₂O₃, Ni₃C, Ni, CO, and C (both amorphous and graphite). Transmission electron microscopy showed an increase in carbon nanopearl size with larger Ni nanoparticles. Raman results concluded that the smaller catalyst resulted in a more crystalline graphitic structure. Finally, the results showed that the 20 nm Ni nanoparticles chemically reacted sooner than the 100 nm Ni nanoparticles.     

Dynamics of SiO2 Buried Layer Removal from Si-SiO2-Si and Si-SiO2-SiC Bonded Substrates by Annealing in Ar

Silicon-on-silicon-carbide substrates could be ideal for high-power and radiofrequency silicon devices. Such hybrid wafers, when made by wafer bonding, contain an intermediate silicon dioxide layer with poor thermal characteristics, which can be removed by high-temperature annealing in an inert atmosphere. To understand the dynamics of this process, removal of 2.4-nm-thick SiO₂ layers from Si-SiO₂-Si and Si-SiO₂-SiC substrates has been studied at temperatures ranging from 1100°C to 1200°C. The substrates were analyzed by transmission electron microscopy, electron energy-loss spectroscopy, secondary-ion mass spectroscopy, and ellipsometry, before and after annealing. For oxide thickness less than 2.4 nm, the activation energy for oxide removal was estimated to be 6.4 eV, being larger than the activation energy reported for removal of thicker oxides (4.1 eV). Under the same conditions, the SiO₂ layer became discontinuous. In the time domain, three steps could be distinguished: bulk diffusion, bulk diffusion with void formation, and bulk diffusion with disintegration. The void formation, predominant here, has an energetic cost that could explain the larger activation energy. The oxide remaining after prolonged annealing corresponds to one layer of oxygen atoms.     

Substrate temperature effect on structural,optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO₂) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T_s) from 250 to 450 °C reduced resistivity of SnO₂ thin films from 18×10⁻⁴ to 4×10⁻⁴▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO₂ films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO₂ films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.     

On the electrical and optical properties of oxide nanolayers produced by the thermal oxidation of metal tin

Thin SnO_2–x layers, 30 nm in thickness, are produced by the thermal oxidation of metal tin nanolayers at a temperature of 450–750°C. The electrical and optical properties of the layers are studied. During the thermal oxidation of tin nanolayers, an unsteady variation in their conductivity is observed. For the oxide films produced at 450 and 550°C, an absorption band at 340 nm (3.65 eV) is detected in the optical spectra. The conductivity-activation energy is determined for samples oxidized to different degrees. On the basis of experimental data and the data reported in publications, an oxidation mechanism controlling the properties of Sn nanolayers is proposed.     

The Effects of Heat Treatment on the Crystallinity and Luminescence Properties of YInGe<Subscript>2</Subscript>O<Subscript>7</Subscript> Doped with Eu<Superscript>3+</Superscript> Ions

Yttrium indium germanate, YInGe₂O₇, doped with Eu³⁺ ions was synthesized by a solid-state reaction using a vibrating mill with metal oxides. The compound was characterized and its optical properties were investigated. The yielded powders were heated at various temperatures from 1100°C to 1400°C in air for 10 h. The X-ray diffraction profiles showed that all peaks could be attributed to the monoclinic YInGe₂O₇ phase at the various calcination temperatures for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. A second phase of In₂O₃ was observed in the X-ray powder diffractometry pattern when the calcination temperature was over 1200°C. Scanning electron microscopy showed that the particle sizes increased significantly with increasing calcination temperature. The calcined powders emitted a reddish luminescence centered at 611 nm under excitation of 393 nm due to the electric dipole transition ⁵D₀ → ⁷F₂. Powders fired at 1200°C were found to have the maximum photoluminescent intensity for YInGe₂O₇ doped with 5 mol.% Eu³⁺ ions. Furthermore, the existence of the second phase caused the decay time to decrease with increasing calcination temperature.     

Structural Properties and Ionic Conductivity of Nanocrystalline Zr5Ti7O24 Ceramic Synthesized by Autoignited Combustion Technique

Nanoparticles of Zr₅Ti₇O₂₄ ceramic have been prepared by the autoignited combustion technique. The phase purity of the ceramic was examined by x-ray diffraction method, yielding lattice parameters of a = 14.3 Å, b = 5.2 Å, and c = 5.1 Å. A narrow size distribution of the nanoparticles was determined by transmission electron microscopy with a peak at 21.55 nm. Coexistence of Zr/TiO₆ octahedra and Zr/TiO₄ tetrahedra was observed in the Raman spectrum. The optical bandgap of the ceramic was found to be 2.36 eV. The sample was pressed into a circular pellet and sintered at 1490°C, obtaining 94.7% of theoretical density. The microstructure of the sintered pellet was analyzed by scanning electron microscopy, and the elemental composition was confirmed by energy-dispersive spectrometry. Impedance spectroscopic analysis of the sample showed that ions are the main source of conduction. Two semicircles in the Cole–Cole plot provide evidence of grain and grain boundary contributions to the conductivity. The total ionic conductivity of the sample was 5.57 × 10^?1 S/m at 700°C. The activation energies of grains and grain boundaries above 500°C were 1.08 eV and 0.72 eV, respectively. Nanocrystalline Zr₅Ti₇O₂₄ ceramic is a promising material for use as an electrolyte in solid oxide fuel cells.     

Molybdenum-Loaded Anatase TiO<Subscript>2</Subscript> Nanoparticles With Enhanced Optoelectronics Properties

The structural, optical and electrical properties of molybdenum nanoparticles (Mo-NPs)-loaded anatase TiO₂ were investigated using x-ray diffraction, UV–Vis diffuse reflectance, and Fourier transform infrared and complex impedance spectroscopy. x-ray diffraction showed that Mo-NPs incorporation induced a decrease in particle size from 30 nm to 21 nm of TiO₂ and TiO₂-Mo, respectively, producing a slight structure expansion. Mo-NPs dispersion resulted in a slight decrease in the optical band gap energy from 3.85 eV to 3.51 eV. Slight shifts towards higher wavelengths were attributed to the change in the acceptor capacity level induced by Mo-NPs. In addition, the ac impedance studies show the effect of Mo-NPs incorporation that appeared to be responsible for conductance of enhancement. The conduction mechanism is based on space charge-limited current via deep levels with different energy positions in the band gap. The temperature dependence of electrical properties showed that both capacitance and conductance of TiO₂-Mo samples increased with increasing temperature. At low frequency, the relaxation phenomenon is related to the surface effect. The results will be beneficial to further developing titanium dioxide photo-catalysts.     

Synthesis and Characterization of Electro-Crystallized Alumina Nanoparticles and Investigation of Their Application in Removal of Cobalt and Cadmium from Seimareh and Karoon Rivers in Iran

Al₂O₃ nanoparticles were successfully synthesized in an electrolytic cell containing two Al sheets as electrodes and an aqueous solution in the presence of an amine. To measure the effect of growth parameters on the properties of alumina nanoparticles, different samples were synthesized under different voltages (5–25 V), electrolyte concentration (0.02–0.1 M) and growth temperatures (10–60°C). X-ray diffraction patterns clearly approved the formation of the Al₂O₃ phase with cubic structure after annealing at 600°C for 2 h, and no sign of impurities was observed. SEM images showed that the particles are quasi-spherical and their mean size ranged from 7 to 270 nm depending on the growth conditions. The ultraviolet–visible results showed that the alumina nanoparticles mainly disperse rather than absorb light. The photoluminescence emission spectrum of nanoparticles showed an original peak at 395 nm, which is related to the electron transition between the levels and the photon emission. The removal of cobalt and cadmium from experimentally polluted water and the Seimareh and Karoon Rivers in Iran has been investigated. The water treatments were studied in an electrochemical cell with polluted water as the electrolyte, and by mixing the alumina nanoparticles with polluted water in a shaker. The results of atomic absorption spectroscopy showed that it is possible to remove about 100% of cadmium from the Seimareh and Karoon rivers. Also, by mixing the alumina nanoparticles with polluted water in a shaker, about 37.77% and 91.06% of cobalt were removed from the Seimareh and Karoon rivers, respectively.     

Effect of Sintering Temperature on Microstructure, Electrical Properties, and Thermal Expansion of Perovskite-Type La0.8Ca0.2CrO3 Complex Oxides Synthesized by a Combustion Method

Perovskite-type La_0.8Ca_0.2CrO₃ complex oxides were synthesized by a combustion method. Microstructural evolution, electrical properties, and thermal expansion behavior of the ceramics were investigated in the sintering temperature range of 1250°C to 1450°C. It was found that the electrical conductivity (σ _e) remarkably improved with increasing sintering temperature from 1250°C to 1400°C, ascribed to the development of microstructural densification, whereas it declined slightly above 1400°C due to generation of excessive liquid. The specimen sintered at 1400°C had a maximum conductivity of 31.6 S cm^?1 at 800°C, and lowest activation energy of 0.148 eV. The improvement of the thermal expansion coefficient (TEC) with increasing sintering temperature was monotonic as a result of the microstructural densification of the materials. The TEC of La_0.8Ca_0.2CrO₃ sintered at 1400°C was about 10.5 × 10^?6 K^?1, being consistent with other components as high-temperature conductors. With respect to microstructure, electrical properties, and thermal expansion, the preferable sintering temperature was ascertained to be about 1400°C, which is much lower than for the traditional solid-state reaction method.