Dielectric properties of bismuth doped CaCu3Ti4O12 ceramics

Ca_1?3x/2Bi_xCu₃Ti₄O₁₂ (x = 0.0–0.3) ceramics were prepared by the conventional solid-state reaction method. X-ray powder diffraction analysis confirmed the formation of cubic CCTO phase except for subtle peaks of CuO. SEM micrographs suggested that the morphologies of doped CCTO ceramics had been sheet-like for high Bi-doping amount, and the dominant grain size decreasing could be seen for the small content of Bi-doping CCTO. Dielectric properties of pure and doped CCTO were investigated in a broad temperature range of 20–420 K. The results showed that bismuth doping could decrease the dielectric loss but suppress the dielectric temperature stability at the same time. Bi doped CCTO ceramics presented different relaxation properties. As to pure CCTO and BCCTO (x = 0.3) only one MW relaxation (Relaxation I) could be found, which moves to higher frequency with temperature increasing. However, two relaxation processes (Relaxation I and II) appear for BCCTO (x = 0.1–0.2). By means of complex impedance spectra analysis and Arrhenius fitting, we successfully separated the different conductive segments and explained the mechanisms of the two relaxation processes. Relaxation I appeared at low temperature could be attributed to the V_O doping energies inside CCTO grains which did not showed significant changing of activation energy after bismuth doping. For Relaxation II at higher temperature than Relaxation I, with activation energy obviously depending on the Bi-ion concentration, may be related with the V_O point defects at the grain boundaries.     

Luminescence at 1.53 μm for a new Er3+-doped transparent oxyfluoride glass ceramic

Transparent 45SiO₂25Al₂O₃5CaO10NaF15CaF₂ glass ceramics doped with different levels of Er³⁺ were prepared. The spherical CaF₂ nanocrystals with 10–20 nm in size were verified to be homogeneously embedded among the glassy matrix. Room temperature absorption and emission spectra corresponding to ⁴I_13/2 ↔ ⁴I_15/2 transitions of Er³⁺ ions in precursor glasses and glass ceramics, respectively had been measured. For glass ceramics, with increasing of Er³⁺ content from 0.1 to 2.0 mol%, the FWHM values of the emission bands increased from 42 to 71 nm; meanwhile, the lifetime of ⁴I_13/2 level slightly reduced. However, both the values of FWHM and lifetime were larger than those of precursor glasses due to the change of ligand field of Er³⁺ ions.     

Structural,optical and morphological properties of La,Cu co-doped SnO2 nanocrystals by co-precipitation method

Sn_0.96−xLa_0.04Cu_xO₂ (0 ⩽ x ⩽ 0.03) nanocrystals have been successfully synthesized by employing a simple co-precipitation method. The crystal structure of the synthesized nanocrystals was found to be tetragonal rutile of tin oxide by using X-ray diffraction technique and was not affected by doping. The change in lattice parameters was discussed based on the secondary phase formation and presence of Cu²⁺/Cu³⁺ in LaSnO₂ lattice. The variation in size and shape of the nanocrystals by Cu-doping was discussed using scanning electron microscope. The chemical stoichiometry of Sn, Cu, La and O was confirmed by energy dispersive X-ray spectra. The best optical transparency and lower absorption observed at Sn_0.97La_0.02Cu_0.01O₂ nanocrystals seems to be optimal for industrial applications especially as transparent electrode. The initial blue shift of energy gap from 3.65 eV (Cu = 0%) to 3.78 eV (Cu = 1%) (ΔE_g ≈ 0.13 eV) is due to the distortion in the crystal structure of the host compound and generation of defects. The red shift of energy gap after Cu = 1% is due to the charge-transfer transitions between the metal ions d-electrons and the SnO₂ conduction or valence band. Lattice mode of SnO₂ at 686 cm⁻¹ in Sn_0.98La_0.02O₂ nanocrystals and anti-symmetric SnOSn stretching mode of the surface bridging oxide around 634–642 cm⁻¹ in Cu doped Sn_0.98La_0.02O₂ nanocrystals was confirmed by Fourier transform infrared spectra.     

Synthesis,crystal structure,luminescent properties and photo degradation of mer-tris(8-Hydroxy-quinolinato-N,O)-indium(iii) hydrate 0.5 methanol solvate

Tris-(8-hydroxyquinioline) aluminium (Alq₃) is widely used in organic light emitting diodes as an emission and electron transport layer. In this study the effect of solvent molecules, in the solid state crystal lattice, on the photoluminescence properties of synthesized mer-tris(8-Hydroxy-quinolinato-N, O)-indium(iii) hydrate 0.5 methanol solvate (mer-[In(qn)₃]⋅H₂O⋅0.5 CH₃OH) was studied. Single crystals were obtained through a recrystallization process and single crystal X-ray diffraction was performed to obtain the unit cell structure. The main absorption peaks were assigned to ligand centered electronic transitions, while the solid state photoluminescence excitation peak at 440 nm was assigned to the 0–0 vibronic state of In(qn)₃. Broad emission at 510 nm was observed and was ascribed to the relaxation of an excited electron from the S₁–S₀ level. A powder sample was annealed at 130 °C for 2 h. A decrease in intensity was observed and could possibly be assigned to a loss of solvent species. To study the photon degradation, the sample was irradiated with an UV lamp for ∼15 h. The emission data was collected and the change in photoluminescence intensity with time was monitored. High resolution X-ray photoelectron spectroscopy (XPS) scans of the O-1s peak revealed that after annealing the binding energy shifted to lower energies indicating a possible loss of the H₂O and CH₃OH present in the crystal. The O-1s peak of the degraded sample indicated the possible formation of CO (∼532.5 eV), COH and OCOH (∼530.5 eV) on the phenoxide ring.     

Effect of annealing temperature on the microstructure and photoluminescence of low resistivity Si/SiN/TaN thin films using magnetron sputtering

A lot of studies have been devoted to the porous Si, erbium-doped Si and Si-embedded in dielectric matrix of SiO or SiN together with long-time conventional furnace annealing. Besides, it is noted that these Si nanostructured films were highly resistive and non-conducting. In this paper, we have investigated the effect of annealing temperature on the microstructure and photoluminescence of low-resistivity Si/SiN/TaN nanocomposite thin films which are deposited by magnetron sputtering and followed by rapid thermal annealing (RTA). All samples are of luminescence and staying low resistivity at about 1462–2162 μΩ cm which increases with increasing annealing temperatures. The asymmetric broad photoluminescence (PL) peak covered the wavelengths of 400–700 nm. The wide visible PL spectra can be deconvoluted into three bands of blue (~ 455 nm), green-yellow (~ 525 nm), and orange emissions (~ 665 nm), which correspond to the emission origins from unsatisfied states in imperfections of interface between the Si:O and SiN:O, located states related to the mixed SiO or SiN bonds in SiN:O layer and nc-Si embedded in SiN:O matrix. The detailed mechanism of broad visible PL was investigated in terms of microstructure and bonding configuration evolution. The relationship between the annealing temperature, microstructure and PL behavior of Si/SiN/TaN multilayer films is discussed and established.     

Investigation on the film-coating mechanism of alumina-coated rutile TiO2 and its dispersion stability

The alumina and alumina-coated rutile TiO₂ samples were synthesized by the chemical liquid deposition method under various pH values and aging temperature. The prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), ζ-potential as well as X-ray photoelectron spectroscopy (XPS). The relationship between pH values, the dispersion stability, crystalline types and microstructure of alumina-coated rutile TiO₂ samples were studied. It is indicated that the coating film exhibited amorphous hydrous alumina (at pH 3–7), boehmite (at pH 7–9) and bayerite (pH > 11), respectively. And the higher aging temperature was in favor of the elevation of boehmite content of coating film. As the boehmite content increased, the dispersion stability was gradually enhanced and the prepared sample exhibited optimum dispersion stability at pH 9 and aging temperature 200 °C, respectively. The increase of steric hindrance and electrostatic repulsion led to the promotion of dispersion stability via coating hydrous alumina film on the surface of rutile TiO₂. The detection of AlO and the significantly enhancement of AlOTi intensity confirmed that the film coating process should be main attributed to both chemical bonding and physical adsorption.     

Fibroblast functionality on novel Ti30Ta nanotube array

In this study, the mechanical substrate and topographical surface properties of anodized Ti30Ta alloy were investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and contact angle measurement. The anodization process was performed in an electrolyte solution containing HF (48%) and H₂SO₄ (98%) in the volumetric ratios 1:9 with the addition of 5% dimethyl sulfoxide (DMSO) at 15 V, 25 V and 35 V for 20 and 40 min, producing a nanotube architecture when anodized at 35 V for 40 min. Human dermal fibroblasts (HDF, neonatal) were utilized to evaluate the biocompatibility of Ti30Ta nanotubes and Ti30Ta alloy after 1 and 3 days of culture. Cellular adhesion, proliferation, viability, cytoskeletal organization and morphology were investigated using fluorescence microscope imaging, biochemical assay and SEM imaging respectively. The results presented identify altered material properties and improved cellular interaction on Ti30Ta nanotubes as compared to Ti30 Ta alloy.     

Catalytic properties of NiSO4/ZrO2 promoted with Fe2O3 for acid catalysis

A series of catalysts, NiSO₄/Fe₂O₃–ZrO₂, for acid catalysis were prepared by the impregnation method, where support, Fe₂O₃–ZrO₂ was prepared by the co-precipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe₂O₃–ZrO₂. The addition of nickel sulfate (or Fe₂O₃) to ZrO₂ shifted the phase transition of ZrO₂ from amorphous to tetragonal to higher temperature because of the interaction between nickel sulfate (or Fe₂O₃) and ZrO₂. 15-NiSO₄/Fe₂O₃–ZrO₂ containing 15 wt.% NiSO₄ and 5 mol% Fe₂O₃, and calcined at 700 °C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe₂O₃ up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO₄/Fe₂O₃–ZrO₂ gradually due to the interaction between Fe₂O₃ and ZrO₂ and consequent formation of FeOZr bond.     

Nanoparticles of the giant dielectric material,calcium copper titanate from a sol–gel technique

The precursor of CaCu₃Ti₄O₁₂ (CCTO) nano particles have been successfully synthesized by sol–gel method at 90 °C. The dried precursor powder was milled and then calcined at 450 °C, 550 °C, 650 °C, 800 °C, 850 °C and 950 °C for 3 h. The phase formation of CCTO was analyzed by step by step using FTIR and XRD. Particle size and shape were evaluated by AFM. The XRD results of the powder calcined at 800 °C indicated the formation of CCTO phase. AFM studies showed that average particle size of the CCTO powder range 90–120 nm. The absorption bands corresponding to vibrations of CaO, CuO and TiOTi were observed at 606, 525 and 463 cm^? 1 using FTIR. The samples sintered at 1040 °C showed the densities as high as 96% of theoretical density. The grain sizes of sintered pellets were determined by FE-SEM. The dielectric properties of prepared samples were studied by LCR meter.     

Synthesis,surface group modification of 3D MnV2O6 nanostructures and adsorption effect on Rhodamine B

Highly uniform 3D MnV₂O₆ nanostructures modified by oxygen functional groups (COO) were successfully prepared in large quantities by an approach involving preparation of vanadyl ethylene glycolate as the precursor. The growth and self-assembly of MnV₂O₆ nanobelts and nanorods could be readily tuned by additive species and quantities, which brought different morphologies and sizes to the final products. With a focus on the regulation of structure, the formation process of 3D architectures of MnV₂O₆ by self-assembly of nanobelts was followed by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The consecutive processes of vanadyl ethylene glycolate and benzoyl peroxide assisted formation of layered structure Mn_0.5V₂O₅·nH₂O, growth of aligned MnV₂O₆ nanobelts, and oriented assembly were proposed for the growth mechanism. The band gap vs. different morphology was also studied. Optical characterization of these MnV₂O₆ with different morphologies showed direct bandgap energies at 1.8–1.95 eV. The adsorption properties of 3D MnV₂O₆ nanostructures synthesized under different conditions were investigated through the removal test of Rhodamine B in aqueous water, and the 3D nanostructures synthesized with 30 g L^?1 benzoyl peroxide showed good adsorption capability of Rhodamine B.     

Phase constitutions of MoSiN anti-oxidation multi-layer coatings on CC composites by fused slurry

To improve the oxidation resistance of MoSi fused slurry coating fabricated in vacuum, MoSiN multi-layer coatings were synthesized on C/C composites in nitrogen atmosphere by fused slurry using same Mo and Si element powders. The phase compositions and microstructures were characterized by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results indicate that the MoSiN coating contains SiC inner layer and MoSi₂/Si main layer, which was similar with MoSi coating. Additionally, a thin outer layer with nano-filiform morphology has been found on the coating surface, which consists of SiC, Si₃N₄, AlN, Al₂O₃ and sialon phase. Oxidation experiments show that the MoSiN multi-layer coating exhibits excellent oxidation resistance at 1400 °C and anti-oxidizing potential ability at 1450 °C.     

Scanning probe microscopy of single Au ion implants in Si

We have studied 5 MeV Au²⁺ ion implantation with fluences between 7 × 10⁷ and 2 × 10⁸ cm^− 2 in Si by deep level transient spectroscopy (DLTS) and scanning capacitance microscopy (SCM). The DLTS measurements show formation of electrically active defects such as the two negative charge states of the divacancy (V₂(/–) and V₂(–/0)) and the vacancy–oxygen (VO) center. It is observed that the intensity of the V₂(/–) peak is lower compared to that of V₂(–/0) by a factor of 5. This has been attributed to a highly localized distribution of the defects along the ion tracks, which results in trapping of the carriers at V₂(–/0) and incomplete occupancy of V₂(/–). The SCM measurements obtained in a plan view show a random pattern of regions with a reduced SCM signal for the samples implanted with fluence above 2 × 10⁸ cm^− 2. The reduced SCM signal is attributed to extra charges associated with acceptor states, such as V₂(–/0), formed along the ion tracks in the bulk Si. Indeed, the electron emission rate from the V₂(–/0) state is in the range of 10 kHz at room temperature, which is well below the probing frequency of the SCM measurements, resulting in “freezing” of electrons at V₂(–/0).     

Room temperature oxidative intercalation with chalcogen hydrides: Two-step method for the formation of alkali-metal chalcogenide arrays within layered perovskites

A two-step topochemical reaction strategy utilizing oxidative intercalation with gaseous chalcogen hydrides is presented. Initially, the Dion-Jacobson-type layered perovskite, RbLaNb₂O₇, is intercalated reductively with rubidium metal to make the Ruddlesden-Popper-type layered perovskite, Rb₂LaNb₂O₇. This compound is then reacted at room-temperature with in situ generated H₂S gas to create RbS layers within the perovskite host. Rietveld refinement of X-ray powder diffraction data (tetragonal, a = 3.8998(2) Å, c = 15.256(1) Å; space group P4/mmm) shows the compound to be isostructural with (Rb₂Cl)LaNb₂O₇ where the sulfide resides on a cubic interlayer site surrounded by rubidium ions. The mass increase seen on sulfur intercalation and the refined S site occupation factor (～0.8) of the product indicate a higher sulfur content than expected for S^2? alone. This combined with the Raman studies, which show evidence for an HS stretch, indicate that a significant fraction of the intercalated sulfide exists as hydrogen sulfide ion. Intercalation reactions with H₂Se_(g) were also carried out and appear to produce an isostructural selenide compound. The utilization of such gaseous hydride reagents could significantly expand multistep topochemistry to a larger number of intercalants.     

Effects of He (90%)/H2 (10%) plasma treatment on electric properties of low dielectric constant SiCOH films

In microelectronics industry, integration of the low dielectric constant (low-k) material films is a continuing issue due to the decreasing device feature size. To improve electric properties, various post-deposition treatments of the low-k material films can be used. In this work, we used room temperature treatment of He/H₂ plasma and investigated the effects of plasma treatment on the electrical properties of low-k SiOCH films. Plasma treatment time changed from 300 to 1800 s. After treatment, the dielectric constant was decreased from 2.9 to 2.48, and the thickness of the low-k SiCOH films changed by only ～5%. The leakage current densities of the low-k SiCOH films were decreased to ～10^?11 A/cm², with treatment time ≥600 s. The breakdown occurred only around 2 V for films plasma-treated for 600 and 900 s. However, for 1800 s treatment time, the breakdown voltage was enhanced dramatically and breakdown occurred at applied voltage higher than 40 V. The surface composition change of the films after treatment was investigated by X-ray photoelectron spectroscopy (XPS). As the plasma treatment time was increased, the intensities of CC/CH and CSi peaks were decreased while the intensities of SiO and CO peaks were increased. It is thought that increase of oxygen content of the SiCOH film, after plasma treatment, contributed to leakage current reduction and breakdown voltage increase.     

Effect of water content in sol on optical properties of hybrid sol–gel derived TiO2/SiO2/ormosil film

Sol–gel derived TiO₂/SiO₂/ormosil hybrid planar waveguides have been deposited on soda-lime glass slides and silicon substrates, films were heat treated at 150 °C for 2 h or dried at room temperature. Different amounts of water were added to sols to study their impacts on microstructures and optical properties of films. The samples were characterized by m-line spectroscopy, Fourier transform infrared spectroscopy (FT-IR), UV/VIS/NIR spectrophotometer (UV–vis), atomic force microscopy (AFM), thermal analysis instrument and scattering-detection method. The refractive index was found to have the largest value at the molar ratio H₂O/OR = 1 in sol (OR means OCH₃, OC₂H₅ and OC₄H₉ in the sol), whereas the thickest film appears at H₂O/OR = 1/2. The rms surface roughness of all the films is lower than 1.1 nm, and increases with the increase of water content in sol. Higher water content leads to higher attenuation of film.     

Synthesis and characterization of a new organic sulphate, [2,3-(CH3)2C6H3NH3]HSO4·H2O

Crystals of a new hybrid compound C₈H₁₂N⁺, HSO₄^?·H₂O were synthesized in aqueous solution and characterized by X-ray diffraction and IR absorption spectroscopy. This compound crystallizes in the orthorhombic non-centrosymmetrical space group P2₁2₁2₁ and an unit cell with a = 5.74(2) Å, b = 9.17(2) Å, c = 21.34(4) Å, V = 1124(6) Å³, and Z = 4. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a,b) planes. The different components are connected by a bi-dimensional network of strong OH…O and NH…O hydrogen bonds. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by DTA–TG and differential scanning calorimetry (DSC) and electrical conductivity measurements were carried out.     

Synthesis of micron-sized porous CeO2SiO2 composite particles for ultraviolet absorption

Micron-sized porous composite particles composed of CeO₂ and SiO₂ nanoparticles were prepared for a UV absorption application by an aerosol spray-drying process from as-prepared CeO₂ nanoparticles, commercial SiO₂, and a polystyrene latex template. The morphology, structure crystallinity and pore size distribution of the as-prepared porous CeO₂SiO₂ composite particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Barrett-Joyner-Halenda (BJH) method, respectively. The porous CeO₂SiO₂ composite particles, with diameters of approximately 10 μm, showed a spherical morphology. As the contents of CeO₂ in the precursor was increased from 0.25 wt% to 1.5 wt%, we observed a change in the morphology of the composite particles from compactly packed porous particles to loosely packed porous particles. The as-prepared CeO₂SiO₂ composite particles were composed of meso- and macropores in the range of 3–200 nm. The effect of the CeO₂ content on the porous composite particles in terms of the UV absorption properties was also investigated by UV-visible spectroscopy. When the content of CeO₂ exceeded 0.75 wt% in the precursor, the particles showed higher UV absorption values compared to those of commercial TiO₂ nanoparticles. The as-prepared porous CeO₂SiO₂ composite particles can therefore be promising materials given their high UV absorption value.     

Formaldehyde on TiO2 anatase (1 0 1): A DFT study

The adsorptions of formaldehyde molecule on the stoichiometric anatase TiO₂ (1 0 1) surface have been studied by first principles calculations. Four types of adsorption have been investigated at 0.25 ML coverage. Two of them are chemical adsorptions and the other two are physical adsorptions. For the chemical adsorptions, C, O atoms in the formaldehyde molecule form two bonds with the O_2c/O_3c and Ti_5c on the anatase (1 0 1) surface. The CO bond in the formaldehyde molecule is elongated and a dioxymethylene structure forms in the two chemical adsorptions. The OTi_5c interaction can be found in the two physical adsorptions and it is the only contacting point at the interface. No serious internal distortion in the formaldehyde molecule can be found in the physical adsorptions. The LDOS and the difference of the charge density are calculated to investigate the interface bonds of the adsorption. As the adsorption coverage increase, the molecules on the surface repel each other and weaken the adsorptions. For example, the chemical adsorption may become physical adsorption at high coverage.     

Surface aspects of discolouration in Bisphenol A Polycarbonate (BPA-PC), used as lens in LED-based products

The surface-related reactions during discolouration of Bisphenol A Polycarbonate (BPA-PC), used as LED lens plates, under thermal stress are studied. X-ray photoelectron spectroscopy (XPS) has been used to monitor the changes in the surface chemistry of BPA-PC plates over a temperature range of 100–140 °C for a period up to 3000 h. Increasing time under thermal stress is associated with the discolouration, and increase in the yellowing index (YI) of PC plastic lens. The XPS results show that discolouration is associated with oxidation at the surface, finding a significant increase in the signal ratio O_1s/C_1s in the XPS spectra of degraded specimens. During thermal ageing, the CH concentration decreases and new oxide features CO and OCO form, with the latter being a support for oxidation at the surface being a major reaction during discolouration. Results also show that irradiation with blue light during thermal ageing accelerates the kinetics of discolouration and the increased O_1s/C_1s ratio in XPS spectra.     

Effects of Zn doping on crystal structure,Raman spectra and superconductivity of SmBa2Cu3O7−δ systems

Polycrystalline SmBa₂Cu_3?xZn_xO_7?δ (SBCZO) (x = 0.0–0.4) samples are prepared by the usual solid-state reaction technique. The effects of Zn doping on the structure, the grain morphology, Raman spectra and electronic transport properties of SBCZO systems have been investigated. The orthorhombic structure of the samples does not change remarkably. The samples become denser and grain boundary becomes unclear with the increase of Zn content. Raman spectra exhibit different features with increasing Zn content which shows that Zn ions act as strong scattering centers to the charge carriers in the CuO₂ planes, enhance the disorder of the CuO₂ planes and increase oxygen depletion in CuO chains. The measurements of the resistivity show that the superconducting transition temperature T_c decreases rapidly and the superconducting transition width increases gradually with increasing Zn contents. Furthermore, the changes of the samples’ normal state resistivity from metallic to semi-conducting behavior show the increase of heterogeneities with increasing Zn content which causes inter-grain or intra-grain disorders. All the results suggest that lattice disorder in the CuO₂ planes, the oxygen content change in CuO chains and local weak superconductivity regions due to the substitution of Zn for Cu are related to the suppression of T_c in the SBCZO systems.