Effect of La doping on microstructure of SnO2 nanopowders prepared by co-precipitation method

A series of La-doped SnO₂ nanopowders with various dopant concentrations were prepared by chemical co-precipitation technique, and the nanopowders prepared were characterized by differential scanning calorimeter (DSC), thermo-gravimetric (TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that La doping can obviously prevent the growth of nanosized SnO₂ crystallites. When the La concentration reaches and surpasses 5 at.%, SnO₂ crystallite size reaches a minimum value and remains almost constant. With the increase of La concentration, La tends to dissolve in the bulk phase of SnO₂ to form solid solution below 10 at.% addition and then starts to disperse onto the surface of the solid solution as a monolayer above 10 at.%. The effect of La doping on hindering crystallite growth can be attributed to the solute drag and lattice distortion resulting from La dissolving in the bulk phase of SnO₂ to form solid solution, rather than the monolayer of La on the surfaces of the SnO₂ powders.     

Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

Influence of Fe2O3 Doping on TiO2 Electrode for Enhancement Photovoltaic Efficiency of Dye-Sensitized Solar Cells

In this work, we report for the first time the improvement of the photovoltaic characteristics of dye-sensitized solar cells (DSSCs) by doping TiO₂ with Fe₂O₃. DSSCs were fabricated using various percentages of Fe₂O₃-doped TiO₂ composite nanoparticles. The Fe₂O₃-doped DSSCs exhibited a maximum conversion efficiency of 5.76% because of the effective electron transport. DSSCs based on Fe₂O₃-doped TiO₂ films showed better photovoltaic performance than cells fabricated with only TiO₂ nanoparticles. This result was attributed to the prevention of recombination between electrons in the TiO₂ conduction band with the dye or electrolytes. A mechanism was suggested based on impedance results, which indicated improved electron transport at the interface of the TiO₂/dye/electrolyte.     

Effects of Nb2O5 Replacement by Er2O3 on elastic and structural properties of 75TeO2-(10 − x)Nb2O5-15ZnO-(x)Er2O3 glass

Tellurite 75TeO₂-(10 − x)Nb₂O₅-15ZnO-(x)Er₂O₃; (x = 0.0-2.5 mol%) glass system with concurrent reduction of Nb₂O₅ and Er₂O₃ addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5 MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x = 0.5 mol% but remained constant between x = 1.0 mol% to x = 2.0 mol%, before increasing back with Er₂O₃ addition at x = 2.5 mol%. The initial drop in shear velocity and related elastic moduli observed at x = 0.5 mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb₂O₅ reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x = 0.5 mol% to x = 2.0 mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er₂O₃ gradually compensated for Nb₂O₅. Further addition of Er₂O₃ (x > 2.0 mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (v_L and v_S) and related elastic moduli at x = 2.5 mol%. FTIR analysis on NbO₆ octahedral, TeO₄ trigonal bipyramid (tbp) and TeO₃ trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x = 0.5 mol% followed by NBO/BO competition at x = 0.5-2.0 mol%. Appearance of ZnO₄ tetrahedra and increase in intensity of TeO₄ tbp absorption peaks at x = 2.0 mol% and x = 2.5 mol% indicate increase in formation of BO.     

Investigation of the structure evolution process in sol-gel derived CaO-B2O3-SiO2 glass ceramics

A sol-gel method was used to prepare CaO-B₂O₃-SiO₂ (CBS) glass powder for making low-temperature cofired ceramics. This paper was focused on the mechanism of hydrolysis and polymerization and also on the structural evolution of xerogel at various temperatures. The xerogel was transformed into glass ceramics containing CaSiO₃ and CaB₂O₄ crystalline phases through nucleation and crystallization processes. The results indicated that the xerogel exhibits [BO₄] or [SiO₄] based three-dimensional network structure whose interstices Ca ions fill in, which becomes more orderly and stable after heat treatments. The CBS glass ceramics through controlled crystallization have a potential as electronic packaging materials.     

Dielectric relaxation study of hydrogen exposure as a source of two-level systems in Al2O3

An important question in the manufacture of superconducting electronics is how to control the two-level systems found in amorphous insulators. The present article shows that hydrogen has a marked impact on the two-level systems in thin films of reactively sputtered Al₂O₃, a standard tunnel oxide for Josephson junctions. The magnitude of dielectric relaxation current in Al₂O₃ films, believed to be caused by two-level systems, is shown to increase monotonically with the flow rate of H₂ into the chamber during deposition. This points toward a potential need for controlling hydrogen during the manufacture of superconducting electronics utilizing Al₂O₃.     

Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.     

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O3 films on CaF2 substrates with transparent (La0.07Sr0.93)SnO3

Epitaxial (La_0.07Sr_0.93)SnO₃ [LSSO] films were deposited on CaF₂ substrates by pulse laser deposition. The (1 0 0)_c orientation of LSSO films was observed only on (1 1 0)CaF₂, whereas (1 1 0)_c orientation was found on (1 1 1)CaF₂ and (1 0 0)CaF₂. (0 0 1) polar axis oriented tetragonal Pb(Zr_0.35Ti_0.65)O₃ films were grown on the fabricated (1 0 0)_cLSSO∥(1 1 0)CaF₂ by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr_0.35Ti_0.65)O₃∥(1 0 0)cLSSO∥(1 1 0)CaF₂ stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm.     

EXAFS and XANES Studies on 3d Transition Metal Intercalation Compounds M x TiS2

Abstract

EXAFS and XANES spectra of Ti K-edge have been measured for 3d transition metal intercalation compounds M _x TiS₂ (M = Mn, Fe, Co and Ni; x ≤ 0.33). We have found that the interatomic distance between Ti and the first nearest neighbor S atoms, R(Ti-S), increases with the guest concentration x. The variation in XANES spectra with x reveals the reduction of the valence state of Ti atoms upon intercalation of M. From these results as well as the M K-edge EXAFS data studied previously, we have proposed a simple model on the local structure of M _x TiS₂ to reproduce the observed values of R(Ti-S) by averaging local shift of S atoms caused by intercalation.     

Synthesis and Single Crystal X-Ray Structure of [Na(H2O)2(C18H15O6SO3)]2

Abstract  [Na(H₂O)₂(C₁₈H₁₅O₆SO₃)]₂ was synthesized by sulfated 5-hydroxy-6,7,4′-trimethoxyisoflavone with concentrated sulfuric acid. Single-crystal X-ray diffraction study indicates that it is a dimeric centrosymmetric species. The coordination polyhedron of each Na(I) atom exhibits a distorted trigonal bipyramidal geometry. The dimeric units are linked by intermolecular hydrogen bonds C–H⋯π, C–H⋯O and O–H⋯O to result in a three-dimensional framework. Graphical Abstract  [Na(H₂O)₂(C₁₈H₁₅O₆SO₃)]₂ was synthesized by sulfated 5-hydroxy-6,7,4′-trimethoxyisoflavone with concentrated sulfuric acid. The coordination polyhedron of each Na(I) atom exhibits a distorted trigonal bipyramidal geometry. The dimeric centrosymmetric units are linked by intermolecular hydrogen bonds C–H⋯π, C–H⋯O and O–H⋯O to result in a three-dimensional framework. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Direct observations of pseudo-binary NdBa2Cu3Ox–Ba3Cu10O13 phase diagram and NdBa2Cu3Ox crystallization under reduced oxygen atmosphere

The pseudo-binary NdBa₂Cu₃O_x–Ba₃Cu₁₀O₁₃ phase diagrams and the crystallization of NdBa₂Cu₃O_x have been in situ observed using high-temperature optical microscope under three different oxygen atmospheres namely 1%, 0.1% and 0.0097% oxygen in argon. It has been observed that the liquidus line becomes narrower both in composition and temperature with decreasing oxygen pressure. This result suggested that under reduced oxygen atmosphere, the NdBa₂Cu₃O_x crystals could only be grown from a peritectic melt consisting of Nd₄Ba₂Cu₂O₁₀ and liquid. The crystallization temperature of NdBa₂Cu₃O_x was found to decrease logarithmically with decreasing oxygen content in the atmosphere.     

Fabrication of Al2O3 Coatings on Metal Substrates by Electrophoretic Deposition by the Addition of Polydimethylsiloxane-Based Organic-Inorganic Hybrid Materials as Binders

Polydimethylsiloxane (PDMS)-based organic-inorganic hybrids have been studied because of their high dielectric strength, heat resistivity, and flexibility. In this study, we fabricated Al₂O₃ coatings on metal substrates with sufficient electrical insulation, heat conductivity, and thermal stability by electrophoretic deposition (EPD) using PDMS-based hybrid binders. The scratch hardness, thermal conductivity, and electrical breakdown strength of the Al₂O₃ coating before and after heat treatment at 300 °C for 500 h were 2.0 N, 3.1 W/mK, and 60 kV/mm, respectively. These results demonstrate the usefulness of EPD using PDMS-based hybrid binders for fabricating flexible heat dissipative substrates used in high-temperature environments.     

Electrical and corrosion properties of the Ti5Si3 thin films coated on glass substrate by APCVD method

Ti₅Si₃ thin films were coated on glass substrate by atmospheric pressure chemical vapor deposition method at different temperatures. Electrical and corrosion properties of the thin films were investigated. The results show that the electrical resistivity of the thin films decreases initially with the increase in deposition temperature. However, it increases with the further increase of the temperature. The lowest electrical resistivity of 107 μΩ⋅cm is obtained at 710 °C. The least corrosion rates of the thin films at 95 °C of 0.10 nm/min and 0.13 nm/min in 1 N and 10 N acid solution and of 0.33 nm/min and 6.55 nm/min in 1 N and 10 N alkali solution, respectively, are obtained by weight-loss measurement method. The corrosion mechanisms of the thin films were also discussed in detail.