Effect of aliovalent dopants on the kinetics of spinodal decomposition in rutile-type TiO2-VO2

The effects of aliovalent dopants on the kinetics of spinodal decomposition in a rutile-type TiO₂-VO₂ system were studied by means of x-ray diffraction and transmission electron microscopy. In this study, as-prepared polycrystalline samples were annealed at 673 k inside the spinodal. For undoped samples, phase decomposition occurred along the [001] direction, and a lamellar structure formed on the nanometer length scale. The phase decomposition kinetics in this system were sensitive to the type of aliovalent dopant; the decomposition rate in a sample doped with Al₂O₃ was more than one order of magnitude higher than a sample doped with Nb₂O₅. These observations could be explained on the basis of the premise that cation interstitial mobility is greater than cation vacancy mobility. The obtained results are consistent with those for a TiO₂-SnO₂ system, indicating that phase separation in both rutile-type oxide systems can be interpreted through a common framework.     

Morphology control in symmetric polymer blends using spinodal decomposition

This paper studied, through modeling and computer simulation, the thermal-induced phase separation phenomenon in a symmetric polymer blend via spinodal decomposition. The one-dimensional model consisted of the Cahn–Hilliard theory for spinodal decomposition, and incorporated the Flory–Huggins–deGennes free energy equation, the slow mode mobility theory and reptation model for polymer diffusion. The numerical results replicated frequently reported experimental observations published in the literature for the early and intermediate stages of spinodal decomposition for symmetric polymer blends. Furthermore, the numerical results indicate that a dimensionless diffusion coefficient may be used as a parameter to control the formation and evolution of the phase-separated regions during spinodal decomposition as a means to customize functional polymeric materials with predefined material properties.     

Spinodal decomposition in the Ta-Mo-Al-N films activated by Mo incorporation: Toward enhanced hardness and toughness

Spinodal decomposition in the transition metal aluminum nitrides, usually triggered by annealing, can enhance hardness via forming coherent nanometer-size domains, but it is still required to activate during fabrication. Herein, Mo was introduced into Ta-Al-N to obtain Ta-Mo-Al-N films by co-sputtering method, which induced two kinds of phase separations, including ~?15?at% Mo induced presence of stable wurtzite AlN phase and ~?28?at% Mo activated spinodal decomposition forming coherent fcc-Ta-Al-N and Mo-Al-N nano-domains. It is found that both hardness and toughness would be worsened by presence of hexagonal wurtzite AlN phase at incorporation of ~?15?at% Mo. On the contrary, once spinodal decomposition took place at ~?28?at% Mo, achieving the joint targets of enhanced hardness and toughness, together with reduced friction and improved wear-resistance. It may provide a new strategy to activate spinodal decomposition during fabrication by alloying additional elements.     

Effect of multilayer structure on high-frequency properties of FeCo/(FeCo)0.63(SiO2)0.37 nanogranular films on flexible substrates

The high-frequency properties of the FeCo-SiO₂ monolayer nanogranular films and FeCo/(FeCo)_0.63(SiO₂)_0.37 multilayer nanogranular films which were elaborated on flexible substrates by magnetron sputtering system were studied. Compared to the monolayer films with the same FeCo content, the multilayer structures comprised of FeCo/(FeCo)_0.63(SiO₂)_0.37 exhibit more excellent properties that the real and imaginary parts of permeability, more than the double value of the monolayer, increase to 250 and 350, respectively. The variation was considered owing to the reduction of the anisotropy field.     

不同载体表面负载TiO2薄膜的离子掺杂研究

TiO₂薄膜是解决TiO₂回收的有效方法，缺点是TiO₂活性低，寻找合适的载体以及提高TiO₂薄膜的光催化活性,是TiO₂负载薄膜技术需要解决的核心问题。研究了13种离子对负载在釉面瓷砖、玻璃、陶瓷、钛片、铝片和不锈钢片6种载体上TiO₂薄膜的掺杂，并从界面材料结构、双电层结构等方面讨论了离子掺杂与载体对TiO₂薄膜光催化活性的影响。结果表明，TiO₂薄膜的离子掺杂效果不仅和离子掺杂浓度、种类有关，而且还与载体类型有关。TiO₂薄膜和非金属载体主要形成复合半导体结构，改善掺杂离子对载流子的捕获能力。金属载体与TiO₂薄膜之间主要形成肖特基势垒，有利于电子与空穴的分离。载体与TiO₂薄膜之间形成的界面双电层结构能改变离子捕获中心与TiO₂半导体费米能级间的相对位置，从而提高或降低离子对载流子的捕获能力。     

Photocatalytic decomposition of acetic acid on TiO2

During room‐temperature transient experiments, acetic acid decomposes photocatalytically on TiO₂ in an inert atmosphere by two parallel pathways. One pathway forms CO₂ and C₂H₆ in a 2:1 ratio, and H₂O forms with lattice oxygen that was extracted from the surface. The other pathway forms CO₂ and CH₄ in a 1:1 ratio. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of different types of water in bentonite clay on hydrate formation and decomposition

The equilibrium and kinetic of hydrate in sediments can be affected by the presence of external components like bentonite with a relatively large surface area. To investigate the hydrate formation and decomposition behaviors in bentonite clay, the experiments of methane hydrate formation and decomposition using the multi-step decomposition method in bentonite with different water contents of 20%, 40% and 60% (mass) were carried out. The contents of bound, capillary and gravity water in bentonite clay and their roles during hydrate formation and decomposition were analyzed. In bentonite with water content of 20% (mass), the hydrate formation rate keeps fast during the whole formation process, and the final gas consumption under different initial formation pressures is similar. In bentonite with the water contents of 40% and 60% (mass), the hydrate formation rate declines significantly at the later stage of the hydrate formation. The final gas consumption of bentonite with the water contents of 40% and 60% (mass) is significantly higher than that with the water content of 20% (mass). During the decomposition process, the stable pressure increases with the decrease of the water content. Hydrate mainly forms in free water in bentonite clay. In bentonite clay with the water contents of 20% and 40% (mass), the hydrate forms in capillary water. In bentonite clay with the water content of 60% (mass), the hydrate forms both in capillary water and gravity water. The bound water of dry bentonite clay is about 3.93% (mass) and the content of capillary water ranges from 42.37% to 48.21% (mass) of the dry bentonite clay.     

Spinodal decomposition as a probe to measure the effects on molecular motion in poly(styrene-co-acrylonitrile) and poly(methyl methacrylate) blends after mixing with a low molar mass liquid crystal or commercial lubricant

The effects on molecular motion observed through early stage phase separation via spinodal decomposition, in melt mixed poly(styrene-co-acrylonitrile) (SAN) containing 25% by weight of acrylonitrile (AN) and poly(methyl methacrylate) (PMMA) (20/80 wt%) blends after adding two low molar mass liquid crystals (CBC33 and CBC53) and two lubricants (GMS and zinc stearate) were investigated using light scattering techniques. The samples were assessed in terms of the apparent diffusion coefficient (D_app) obtained from observation of phase separation in the blends. The early stages of phase separation as observed by light scattering were dominated by diffusion processes and approximately conformed to the Cahn-Hilliard linearised theory. The major effect of liquid crystal (LC) was to increase the molecular mobility of the blends. The LC generally increased the Cahn-Hilliard apparent diffusion coefficient, D_app, of the blend when added with concentrations as low as 0.2 wt%. GMS and zinc stearate can also improve the mobility of the blend but to a lesser extent and the effect does not increase at higher concentration. On the other hand, the more LC added, the higher the mobility. In all systems the second derivative of the Gibbs free energy becomes zero at the same temperature. The improved mobilities therefore seem to arise from changes in dynamics rather than thermodynamic effects.     

Strain effects in epitaxial La-doped SrSnO3 films on lattice-matched PMN-PT substrates

Here we report the effect of the strain states on the structure, optical and electrical transport properties of the La_0.05Sr_0.95SnO₃ (LSSO) thin films grown epitaxially on (001)-oriented 0.70 Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PMN-PT) substrates by pulsed laser deposition. X-ray diffraction results indicate that the films are fully strained up to at least 100 nm thickness, and the in-plane compressive strain gradually releases in thicker films. High-resolution transmission electron microscopy characterizations demonstrate that the LSSO films were grown coherently on PMN-PT(001) substrates. With varying the thicknesses of the fully strained films from 20 to 100 nm, the electrical transport properties are improved significantly. A lowest room-temperature resistivity of 1.88 mΩcm and the highest mobility of 28.1 cm²/Vs are obtained in the 100 nm film. The optical band gap determined from spectroscopic ellipsometry is found to increase from 4.58 to 4.88 eV with the film thicknesses varying from 20 to 500 nm. The results imply that the LSSO epitaxial films exhibit tunable electrical performances and optical band gaps through strain, which may have potential applications in optoelectrical devices.     

Numerical simulation of substrate effects on spinodal decomposition in polymer binary mixture: morphology and dynamics

The characteristic features of the morphology and dynamics of binary mixture for substrate-directed spinodal decomposition (SDSD) in three dimensions have been studied using numerical simulations. The simulation results show that the formation of the wetting layer on the substrate interface follows the power-law growth. It is found that the continuous influence of anisotropic diffusive behavior arose by wetting of substrate induces the wetting component spreading onto the interface of the substrate randomly. The phase morphology and averaged size in the vicinity of the substrate fluctuate greatly due to the wetting of the substrate. The self-similar evolution of the cross-sections parallel and perpendicular to the substrate interface is discussed by relevant scale law functions, respectively. And the mechanisms of the growth in both the parallel and perpendicular directions are also investigated.     

Chemical solution deposition of epitaxial indium- and aluminum-doped Ga2O3 thin films on sapphire with tunable bandgaps

Compared to the vacuum-required deposition techniques, the chemical solution deposition (CSD) technique is superior in terms of low cost and ease of cation adjustment and upscaling. In this work, highly epitaxial indium- and aluminum-doped Ga₂O₃ thin films are deposited using a novel CSD technique. The 2θ, rocking curve, and φ-scan modes of x-ray diffraction (XRD) measurements and high-resolution transmission electron microscopy suggest that these thin films have a pure beta phase with good in- and out-of-plane crystallization qualities. The effect of incorporating indium and aluminum into the crystallization process is studied using high-temperature in situ XRD measurements. The results indicate that indium and aluminum doping can shift the crystallization of the thin films to lower and higher temperatures, respectively. Additionally, ultraviolet-visible spectroscopy measurements indicate that the bandgap of the sintered thin films can be tuned from 4.05 to 5.03 eV using a mixed precursor solution of In:Ga = 3:7 and Al:Ga = 3:7. The photodetectors based on the (InGa)₂O₃, pure Ga₂O₃, and (AlGa)₂O₃ samples exhibit the maximum photocurrents at 280, 255, and 230 nm, respectively. The results suggest that the described CSD technique is promising for producing high-quality bandgap tunable deep-ultraviolet photoelectrical and high-power devices.     

Numerical simulation of substrate effects on spinodal decomposition in polymer binary mixture: Effects of the surface potential

The surface-directed spinodal decomposition (SDSD) of polymer binary mixture with different values of surface potential is numerically simulated in three-dimension (3D) by cell dynamic systems (CDS). Furthermore, the growth laws of the wetting layer are theoretically analyzed by the current equation and the dynamical scaling. The results show that the thickness of the wetting layer increases with the increasing surface potential. The crossover, which is later for larger values of surface potential, appears in the evolution curve of the wetting layer. Before the crossover, the growth law is the surface potential dependant growth law. Subsequently, the growth law is the typical Lifshitz-Slyozov (LS) growth law. The results indicate that the surface potential can result in the mutual transformation between completely wetting and partially wetting for the substrate interface. It can be found that the higher surface potential leads to the faster and stronger transmission of the effect of the substrate on the spinodal decomposition in the bulk.     

Transient measurements of lattice oxygen in photocatalytic decomposition of formic acid on TiO2

In the absence of gas-phase O₂, formic acid extracted lattice oxygen from TiO₂ during photocatalytic decomposition (PCD) at room temperature. The amount of oxygen extracted was determined by interrupting PCD of a monolayer of formic acid after various reaction times and measuring O₂ uptake in the dark. After surface oxygen was depleted by PCD, oxygen diffused from the bulk to replenish the surface oxygen vacancies. The rate of oxygen diffusion to the surface was determined by measuring O₂ uptake after various dark times. A small fraction of the CO₂ that formed during PCD remained on the reduced sites of the TiO₂ surface, but this CO₂ was displaced by O₂ adsorption at room temperature.     

Yttrium incorporation in Cr2AlC: On the metastable phase formation and decomposition of (Cr,Y)2AlC MAX phase thin films

Herein we report on the synthesis of a metastable (Cr,Y)₂AlC MAX phase solid solution by co-sputtering from a composite Cr–Al–C and elemental Y target, at room temperature, followed by annealing. However, direct high-temperature synthesis resulted in multiphase films, as evidenced by X-ray diffraction analyses, room-temperature depositions, followed by annealing to 760°C led to the formation of phase pure (Cr,Y)₂AlC by diffusion. Higher annealing temperatures caused a decomposition of the metastable phase into Cr₂AlC, Y₅Al₃, and Cr-carbides. In contrast to pure Cr₂AlC, the Y-containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y-content dependent and was increased by ∼200°C for 5 at.% Y compared to Cr₂AlC. Calculations predicting the metastable phase formation of (Cr,Y)₂AlC and its decomposition are in excellent agreement with the experimental findings.     

Electrochemical formation and characterization of porous titania (TiO2) films on Ti

Galvanostatically and potentiostatically formed surface oxide films on titanium in H₂O₂ free and H₂O₂ containing H₂SO₄ solutions were investigated. Conventional electrochemical techniques, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy, were used. In the absence of H₂O₂, the impedance response indicated a stable thin oxide film which depends on the mode of anodization of the metal. However, in the presence of H₂O₂ the film characteristics were changed. A significant decrease in the corrosion resistance of the surface film was recorded. The film characteristics were also found to be affected by the mode of oxide film growth and polarization time. The EIS results and the impedance data fitting to equivalent circuit models have shown that the oxide film consists of two layers. The electrochemical characteristics of the anodic films formed under different conditions have been discussed.     

Characterization of La0.67Sr0.33MnOz thin films synthesized by metal-organic decomposition on different substrates

La_0.67Sr_0.33MnO_z (LSMO) thin films were synthesized by means of metal-organic decomposition on the substrates including amorphous quartz, (1 0 0) Si chip, (1 0 0) MgO single crystal and polycrystalline Al₂O₃ ceramic plate. The structure and magnetotransport properties of the films were characterized. X-ray diffraction spectra show that all samples are polycrystalline with (2 0 2) preferred orientation. All films present metal–insulator transition and enhanced magnetoresistance (MR) effect below metal–insulator transition peak temperature (T_p). At room temperature (RT) low-field magnetoresistance effect (LFMR) and linear change of resistivity under applied field are exhibited by all the films. These magnetotransport properties were first ascribed to the porous structural characteristics in the films observed by atomic force microscope. Furthermore, the LSMO film synthesized on (1 0 0) MgO substrate presents a bit different magnetic properties and magnetotransport from the other samples, including broad ferromagnetic–paramagnetic transition zone, lower T_p and weaker LFMR at RT. However, for the samples synthesized on the other substrates, the LFMR effect is very similar to each other and their MR ratio reaches near 5% under 10 kOe field. Thus the substrate effect of LSMO film on (1 0 0) MgO is more intensive than that of the other samples.     

Regulating crystal structure and ferroelectricity in Sr doped HfO2 thin films fabricated by metallo-organic decomposition

HfO₂ based binary ferroelectric oxides are promising candidate for nonvolatile memory devices due to their compatibility with the current Si-based technology. In this work, Sr doped HfO₂ (Sr:HfO₂) ferroelectric thin films with Sr concentration from 0% to 10?mol% were prepared on the platinum electrodes by metallo-organic decomposition (MOD). It was demonstrated that uniform Sr:HfO₂ thin films with extremely low roughness can be achieved and crystallized by MOD under a 700?°C annealing process. A wake-up stage was believed more essential for the ferroelectricity of the MOD derived Sr:HfO₂ thin film, since the remnant polarization of 13.3 µC/cm² and high dielectric constant of 30 were obtained after 10⁵ cycling tests. The transformation from monoclinic phase to cubic phase was observed with increasing the Sr concentration and the thickness of the films. X-ray photoelectron spectroscopy analysis confirmed the bonding type of O-Hf-O and O-Sr-O bonds in the film. The microscopic crystal structure of ferroelectric orthorhombic phase was observed by high resolution transmission electronic microscope. The intrinsic ferroelectricity of Sr:HfO₂ film was demonstrated by the hysteresis polarization-voltage loops and distinct current peaks in the current-voltage curve. Stable domain structure and its switching dynamics were monitored by piezoresponse force microscopy, indicating the native polarization of Sr:HfO₂. This work will provide a controllable routine to fabricate ferroelectric HfO₂ based thin films using MOD method.     

Deposition of REBCO with different rare earth elements on CeO2 buffered technical substrates by fluorine-free metal organic decomposition route

Pristine REBa₂Cu₃O_7?δ (REBCO, RE with Yb, Y, Dy, Gd, Eu and Sm) superconducting films are deposited on CeO₂ buffered technical substrates by fluorine-free metal organic decomposition (FF-MOD) method. The structure and superconductivity are comprehensively characterized and studied. Under the optimal conditions, all the films form good crystallinity and strong biaxial texture examined by XRD. A smooth and dense morphology is observed in the YBCO, GdBCO, EuBCO and SmBCO films. For all the films, T_c^onset values are lower than that in the corresponding bulk materials, implying a certain degree of microstructure defects (e.g., RE-Ba substitution, and/or oxygen vacancies). Among all the compositions, the GdBCO film shows a high T_c^onset value (>90 K), while the high J_c values are achieved at 77 K in broad field regime, also being with the largest maximum pinning force of 2.3 GN m^?3. On the other hand, a high J_c value (at 77 K self-field) is obtained in the YBCO film, however, the rapid J_c decay with increase of the magnetic fields is found. These results reveal that defects in the YBCO film could only serve as weak pinning centers at least at 77 K. According to Dew-Hughes fitting models, we found that the primary pinning mechanism in all the REBCO films attributes to typical 2D non-superconducting phase i.e., Normal surface pinning. This work for the first time systemically demonstrates feasibility of deposition REBCO with various rare earth elements on technical substrates through the FF-MOD route, and provides a guideline for further growth of nano-composited and mixed rare earth REBCO films.     

Stoichiometric photocatalytic decomposition of pure water in Pt/TiO2 aqueous suspension system

The influence of the direction of ultraviolet irradiation upon the yields of the photocatalytic decomposition of pure water has been investigated in Pt/TiO₂ aqueous suspension system. The yields of the photocatalytic decomposition irradiated from the top of the reaction cell are about 10³ times higher than those irradiated from the bottom. The difference seems due to the reverse reaction of the formed H₂ and O₂ in the suspension.     

Electrophoretic deposition of nanocrystalline TiO2 films on Ti substrates for use in flexible dye-sensitized solar cells

Nanocrystalline TiO₂ films were prepared on flexible Ti-metal sheets by electrophoretic deposition followed by chemical treatment with tetra-n-butyl titanate (TBT) and sintering at 450 °C. X-ray diffraction (XRD) analysis indicates that TBT treatment led to the formation of additional anatase TiO₂, which plays an important role in improving the interconnection between TiO₂ particles, as well as the adherence of the film to the substrate, and in modifying the surface properties of the nanocrystalline particles. The effect of TBT treatment on the electron transport in the nanocrystalline films was studied by intensity-modulated photocurrent spectroscopy (IMPS). An increase in the conversion efficiency was obtained for the dye-sensitized solar cells with TBT-treated nanocrystalline TiO₂ films. The cell performance was further optimized by designing nanocrystalline TiO₂ films with a double-layer structure composed of a light-scattering layer and a transparent layer. The light-scattering effect of the double-layer nanocrystalline films was evaluated by diffuse reflectance spectra. Employing the double-layer nanocrystalline films as the photoelectrodes resulted in a significant improvement in the incident photo-to-current conversion efficiency of the corresponding cells due to enhanced solar absorption by light scattering. A high conversion efficiency of 6.33% was measured under illumination with 100 mW cm⁻² (AM 1.5) simulated sunlight.