Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Preparation of compact Al2O3 film on metal for oxidation resistance by polyvinylpyrrolidone

Oxidation resistance of metal at high temperature can be improved by an environmentally friendly solution deposition approach. Stable precursor solution with high oxide concentration, favorable viscosity and low surface tension was prepared using aluminum sec-butoxide (ASB) and polyvinylpyrrolidone (PVP) as starting raw materials. Alumina sol-gel films were deposited onto metal by spin-coating followed by heat treatment. When PVP was added according to an amount of 50 mg/mL into a sol with an ASB/H₂O molar ratio of 1:35, the as-obtained sol exhibited favorable gelation time and viscosity. The surface tension of the alumina sol with PVP was examined to be lower by 32% than the sol (ASB:H₂O = 1:100) without PVP. TG-DTA analyses show the densification of the alumina gel film with PVP was progressed within a wide temperature range from 200 to 650 °C. Crack-free Al₂O₃ film with a thickness up to 1.5 μm was successfully produced on metallic substrate by three spin-coating cycles. SEM and XRD analyses revealed the gel film transformed into compact α-Al₂O₃ material after calcined at 1,000 °C for 0.5 h. The weight gained by the samples during firing at 1,000 °C indicated that the Al₂O₃ coating film could reduce the rate of oxidation by ∼81%. The hardness of the Al₂O₃ film coated metal was higher by 260% than the uncoated metal that was calcined at 1,000 °C for 0.5 h. It was confirmed by adhesion test that both the alumina/PVP hybrid film and the as-produced α-Al₂O₃ coating film had strong adhesion.     

Formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> bilayer using atomic layer deposition and its application to dynamic random access memory

To enhance film conformality together with electrical property suitable for dynamic random access memory (DRAM) capacitor dielectric, the effects of oxidant and post heat treatment were investigated on aluminum and titanium oxide (Al₂O₃–TiO₂) bilayer (ATO) thin film formed by atomic layer deposition method. For the conformal deposition of Al₂O₃ thin film, the O₃ oxidant required a higher deposition temperature, more than 450 °C, while H₂O or combined oxygen sources (H₂O+O₃) needed a wide range of deposition temperatures ranging from 250 to 450 °C. Conformal deposition of the TiO₂ thin film was achieved at around 325 °C regardless of the oxidants. The charge storage capacitance, measured from the ATO bilayer (4 nm Al₂O₃ and 2 nm TiO₂) deposited at 450 °C for Al₂O₃ and 325 °C for TiO₂ with O₃ oxidant on the phosphine-doped poly silicon trench, showed about 15% higher value than that of 5 nm Al₂O₃ single layer thin film without any increase of leakage current. To maintain the improved electrical property of the ATO bilayer for DRAM application, such as enhanced charge capacitance without increase of leakage current, upper electrode materials and post heat treatments after electrode formation must be selected carefully. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

Characteristics of Ag/Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/p-Si heterostructure prepared by sol-gel processing

The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi_3.25La_0.75Ti₃O₁₂ (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10⁻⁸ A/cm² within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.     

Effect of gamma-irradiation on surface and catalytic properties of nanocrystalline CuO,NiO and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> supported on alumina

The effect of γ-irradiation on surface and catalytic properties of CuO/Al₂O₃, NiO/Al₂O₃ and Fe₂O₃/Al₂O₃ was investigated. The techniques employed were XRD, nitrogen adsorption at −196 °C and catalytic conversion of ethanol and isopropanol at 250–400 °C using micropulse technique. The results showed that the supported solids being calcined at 400 °C consisted of well crystallized CuO, NiO, Fe₂O₃ and AlOOH phases. The AlOOH crystallized into a poorly crystalline γ-Al₂O₃ upon heating at 600 °C. All phases present in different solids calcined at 400 and 600 °C showed that these solids are of nanocrystalline nature measuring an average crystallite size between 6 and 85 nm. The crystallite size of crystalline phases present was found to be much affected by the dose of γ-rays and the nature of the metal oxide. This treatment resulted in a progressive increase in the specific surface area reaching to a maximum limit at a dose of 0.8 MGy. The dose of 1.6 MGy exerted a measurable decrease in the S _BET. A radiation dose of 0.2 to 0.8 MGy brought about a progressive significant decrease in the catalytic activity of all the catalytic systems investigated. All the catalytic systems retained their high activity upon exposure to a dose of 1.6 MGy. The rise in precalcination temperature of the systems investigated from 400 to 600 °C brought about a measurable increase in their catalytic activity in the conversion of alcohols.     

Sol–gel derived 12BaO·7Al<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films using metal alkoxides

The 12BaO·7Al₂O₃ (B12A7) thin films have been prepared via sol–gel process. Optical and electrical properties of B12A7 films have been investigated. The films were coated on soda lime float glass by the dip coating process, and annealed in air and hydrogen (H₂) at 450 °C for 2 h. The UV absorption edge was red shifted for films annealed in H₂ atmosphere. The B12A7 films had high transparency about 90% in wide visible range with maximum of 95% at 575 nm wavelength. The sheet resistance of the 300 nm films corresponding to 90.57 and 0.974 kΩ per square has been observed for air and H₂ annealed, respectively.     

Monolithic FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia oxidation and nitrous oxide decomposition

(1.2–8.3)%FeO_х/Al₂O₃ monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH₃ oxidation and in the selective decomposition of N₂O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe₂O₃ particles localized on the Al₂O₃ surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe₂(C₂O₄)₃ · 5H₂O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO₃)₃ · 9H₂O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeO_х/Al₂O₃ catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeO_х particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeO_х/Al₂O₃ samples prepared using iron nitrate.     

Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Synthesis and properties of CaZrO<Subscript>3</Subscript> films on YSZ electrolyte surface

CaZrO₃ films are studied that were obtained on ceramic supports of solid electrolyte of ZrO₂ + 9 mol % Y₂O₃ (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the film-forming solution. Vickers microhardness of the CaZrO₃ films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C by comparison of impedance spectra of clean supports and supports with a film coating.     

Towards high-performance cathode materials for lithium-ion batteries: Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-coated LiNi<Subscript>0.8</Subscript>Co<Subscript>0.15</Subscript>Zn<Subscript>0.05</Subscript>O<Subscript>2</Subscript>

Zn-doped LiNi_0.8Co_0.2O₂ exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi_0.8Co_0.15Zn_0.05O₂ as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al₂O₃ layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂ cathode delivers a highly reversible capacity of 182 mA h g^?1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi_0.8Co_0.15Zn_0.05O₂ cathode. The enhanced electrochemistry performance can be attributed to the Al₂O₃-coated protective layer, which prevents the direct contact between the LiNi_0.8Co_0.15Zn_0.05O₂ and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂, which rationally illuminates the protection mechanism of the Al₂O₃-coated layer.     

Phase equilibria in the system Li<Subscript>2</Subscript>O-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The subsolidus region of the Li₂O-MgO-B₂O₃ system has been studied by X-ray powder diffraction and differential thermal analysis. Isothermal sections at 500–550 and 650–700°C have been designed. The following complex borates have been found to form: at 500–550°C, Li₂MgB₂O₅ and LiMgBO₃ are formed; at 650–700°C, a new phase Li₄MgB₂O₅ is formed along with LiMgBO₃; and at 5500–600°, Li₂MgB₂O₅ is formed.     

Solid-phase synthesis of intermetallic compounds Al<Subscript>13</Subscript>Co<Subscript>4</Subscript>, Al<Subscript>13</Subscript>Fe<Subscript>4</Subscript>, and Al<Subscript>13</Subscript>Co<Subscript>2</Subscript>Fe<Subscript>2</Subscript>

Intermetallic compounds Al₁₃Co₄, Al₁₃Fe₄, and Al₁₃Co₂Fe₂ were obtained by solid-phase synthesis in air at temperatures below 600°C using precursor metals subjected to mechanochemical preactivation. The phase composition of the synthesized aluminides and composites Al₁₃Co₄/SiO₂ and Al₁₃Fe₄/SiO₂ was analyzed.     

Physicochemical study of composite gel in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> system

We show a feasibility of preparing a highly homogeneous composite gel (CG) based on hydrolysis products of Al₂O₃-ZrO₂ salts. The phase composition of a sample calcined at 1250°C for 2 h is as follows: α-Al₂O₃, t-ZrO₂, and m-ZrO₂ where the t-ZrO₂/m-ZrO₂ phase ratio ranges from 2.8 to 3.8 depending on gel preparation conditions. The investigative tools used are powder X-ray diffraction, differential thermal analysis (atmosphere: Ar), and IR spectroscopy.     

Rational design of double-confined Mn<Subscript>2</Subscript>O<Subscript>3</Subscript>/S@Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocube cathodes for lithium-sulfur batteries

Due to the high specific capacities and environmental benignity, lithium-sulfur (Li-S) batteries have shown fascinating potential to replace the currently dominant Li-ion batteries to power portable electronics and electric vehicles. However, the shuttling effect caused by the dissolution of polysulfides seriously degrades their electrochemical performance. In this paper, Mn₂O₃ microcubes are fabricated to serve as the sulfur host, on top of which Al₂O₃ layers of 2 nm in thickness are deposited via atomic layer deposition (ALD) to form Mn₂O₃/S (MOS) @Al₂O₃ composite electrodes. The MOS@Al₂O₃ electrode delivers an excellent initial capacity of 1012.1 mAh g^?1 and a capacity retention of 78.6% after 200 cycles at 0.5 C, and its coulombic efficiency reaches nearly 99%, giving rise to much better performance than the neat MOS electrode. These findings demonstrate the double confinement effect of the composite electrode in that both the porous Mn₂O₃ structure and the atomic Al₂O₃ layer serve as the spacious host and the protection layer of sulfur active materials, respectively, for significantly improved electrochemical performance of the Li-S battery.     

Phase relations in the MgO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Phase relations in the MgO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. No ternary compounds have been found in the system. Quasi-binary sections have been the 600°C determined and isothermal section of the system has been constructed.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

Investigation of catalytic activity of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles in the thermal decomposition of ammonium perchlorate

A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al₂O₃. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe₂O₃ powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al₂O₃ composites by means of reactive sintering at moderate temperatures.     

Tin Acetylacetonate as a Precursor for Producing Gas-Sensing SnO<Subscript>2</Subscript> Thin Films

To expand the range of precursors used in the sol–gel technology for applying nanostructured SnO₂ thin films promising as components of semiconductor chemical gas sensors, the efficiency of using tin acetylacetonate solutions with various precursor concentrations was demonstrated. It was determined that finely divided SnO₂ with a crystallite size of 3–4 nm (cassiterite) can be obtained by hydrolysis by atmospheric moisture in the course of solvent evaporation at room temperature. Using tin acetylacetonate solutions with various precursor concentrations for applying SnO₂ thin films by dip coating to the surface of rough ceramic Al₂O₃-based substrates with platinum interdigital electrodes and a microheater resulted in significant differences in microstructure, continuity, thickness, and porosity of the produced coatings. In a lower-concentration (0.13 mol/L) tin acetylacetonate solution, a multilayer dense continuous SnO₂ coating was applied, whereas in a higher-concentration (0.25 mol/L) solution, the formed layer comprised aggregated nanoparticles 30–60 nm in size and had much more defects and higher porosity. The sensitivity of the obtained thin-film nanostructures to the most practically important gaseous analytes: CO, H₂, CH₄, CO₂, and NO₂. The produced two-dimensional nanomaterials were shown to be promising for detecting carbon monoxide at 200–300°C in dry air.     

Effect of pretreatment conditions on the catalytic activity of coprecipitated Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> catalyst in soot oxidation

The temperature of soot oxidation and efficiency of Ce_0.5Zr_0.5O₂ catalyst depends on its morphology, which determines the area of intergranular contact between the solid substrate and the catalyst. The temperature-programmed reduction in hydrogen to 1000°C and oxidation at 500°C (redox cycles) cause the mobility of oxygen in oxide to be enhanced and decrease the temperature of soot combustion. Oxidation of soot in the air flow on the Ce_0.5Zr_0.5O₂ catalyst result in its activation. Reuse of the catalyst decreases the temperature of soot oxidation.