Capacitance performance enhancement of TiO2 doped with Ni and graphite

Nano-amorphous TiO2 was prepared by a sol-gel method. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the composite electrode material (TiO2-NiO-C) is made of powder with a grain size of 36.2 nm. Doping of nickel and graphite can increase the electrical conductivity and the specific surface area of nano-amorphous TiO2. The electrochemical properties of TiO2-NiO-C,such as self-discharge, leakage current, and cycle life, were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge test. With a charge-discharge current density of 500 mA/g, the specific capacity of the TiO2-NiO-C composite material reaches 12.88 mAh/g. Also, the expense of capacity is only 3.88% after 500 cycles. The electrochemical capacitor with the electrode material of TiO2-NiO-C shows excellent capacity and cycling performance.     

Photoresponse and donor concentration of plasma-sprayed TiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript>-ZnO electrodes

The photoelectrochemical characteristics of plasma-sprayed porous TiO₂, TiO₂-5%ZnO, and TiO₂-10%ZnO electrodes in 0.1 N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology, and composition of the electrodes were analyzed using an electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscopy, and x-ray diffraction. The results indicate that the sprayed electrodes have a porous microstructure, which is affected by the plasma spray parameters and composition of the powders. The TiO₂-ZnO electrodes consist of anatase TiO₂, rutile TiO₂, and Zn₂Ti₃O₈ phase. The photoresponse characteristics of the plasma-sprayed electrodes are comparable to those of single-crystal TiO₂, but the breakdown voltage is close to 0.5 V (versus that of a saturated calomel electrode). The short-circuit photocurrent density (J _SC) increases with a decrease of donor concentration, which was calculated according to the Gartner-Butler model. For the lowest donor concentration of a TiO₂-5%ZnO electrode sprayed under an arc current of 600 A, the short-circuit J _SC is approximately 0.4 mA/cm² higher than that of the TiO₂ electrodes under 30 mW/cm² xenon light irradiation. The J _SC increases linearly with light intensity. The original version of this paper was published as part of the DVS Proceedings: “Thermal Spray Solutions: Advances in Technology and Application,” International Thermal Spray Conference, Osaka, Japan, 10–12 May 2004, CD-Rom, DVS-Verlag GmbH, Düsseldorf, Germany.     

Phase Relations in the System TiO<Subscript>2</Subscript>-V<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> under Oxidizing and Reducing Conditions

The target of this work was to investigate the phase development in the catalyst system consisting of TiO₂ (Anatase) and V₂O₅ (Shcherbinaite) under several gas atmospheres. Thus a set of V₂O₅/TiO₂ specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700 °C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525 °C the formation of a Rutile solid solution (Rutile-ss) containing VO _x species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V₂O₅ to V₂O₃ was found by X-ray diffraction measurements. There is no miscibility up to 1300 °C followed by the formation of V₂TiO₅ (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO₂ remains without much alteration. The two phases V₂Ti₇O₁₇ and V₂Ti₃O₉ (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.     

Preparation of TiO<Subscript>2</Subscript> Nanopowders by Plasma Spray and Characterizations

TiO₂ powders with the range of 10-60 nm were prepared successfully by plasma spray in the self-developed plasma spray equipment. The prepared nanopowders were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that the prepared TiO₂ nanopowders were the mixture of anatase phase and rutile phase, the main phase was anatase. There were O, Ti, and C elements in powders; Ti element still existed in tetravalent. The photocatalytic degradation of methyl orange indicated that all methyl orange (20 mg/L) can be degraded fully when the addition of prepared TiO₂ nanopowders and illumination time were 1 g/L and 150 min, respectively.     

Effects of defects generated in ALD TiO<Subscript>2</Subscript> films on electrical properties and interfacial reaction in TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si system upon annealing in vacuum

Thin TiO₂ layers grown at 130°C on SiO₂-coated Si substrates by atomic layer deposition (ALD) using TTIP and H₂O as precursors were annealed, and the effects of the annealing temperature on the resulting electrical properties of TiO₂ and the interface properties between a Pt electrode and TiO₂ were examined using transmission line model (TLM) structures. The as-deposited TiO₂ thin film had an amorphous structure with OH groups and a high resistivity of 6×10³Ω-cm. Vacuum annealing at 700 °C transformed the amorphous film into an anatase structure and reduced its resistivity to 0.04Ω-cm. In addition, the vacuum-annealing of the TiO₂/SiO₂ structure at 700°C produced free silicon at the TiO₂-SiO₂ interface as a result of the reaction between the Ti interstitials and SiO₂. The SiO₂ formed on the TiO₂ surface caused a Schottky contact, which was characterized by the TLM method. The use of the TLM method enabled the accurate measurement of the resistivity of the vacuum-annealed TiO₂ films and the characterization of the Schottky contacts of the metal electrode to the TiO₂.     

Chemical observation of anodic TiO<Subscript>2</Subscript> for biomaterial application

Anodic TiO₂ film on Ti a substrate was fabricated at 170 V in sulfuric acid solutions containing phosphoric acid and hydrogen peroxide. The pores in the oxide layer were not uniform in size, shape, or direction of growth, particularly near the interface between the substrate and the oxide layer, compared with those of the surface layer. The formation of an irregular type of pores seemed to be caused by the spark discharge phenomena, which occurred extensively when the anodic voltage was increased. The pore diameter and the cell size increased and the number of cells per unit area decreased over time. From the analysis of chemical states in the XPS spectrum, the incorporated phosphate species were found mostly in the forms of HPO₄, PO₄, and PO₃. In addition, Ti, O, and P were well dispersed in TiO₂ oxide film, as shown in the results of element mapping analyses by an energy dispersive X-ray spectrometer. An SEM observation of osteoblast-likes cells grown on treated TiO₂ oxide film samples for 24h showed clear differences in cell density and spreading pattern. MC3T3 osteoblast-like cells were flat with a polygonal configuration and were attached to the substrate by cellular extensions.     

Effect of a surface treatment for LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> cathode material in lithium secondary batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode material was surface-treated to improve its electrochemical performance. Al₂O₃ nanoparticles were coated onto the surface of LiNi_1/3Co_1/3Mn_1/3O₂ powder using a sol-gel method. The as-prepared Al₂O₃ nano-particle was identified as the cubic structure of Al₂O₃. XRD showed that the LiNi_1/3Co_1/3Mn_1/3O₂ structure was not affected by the Al₂O₃ coating. With a coating of 3 wt.% Al₂O₃ on LiNi_1/3Co_1/3Mn_1/3O₂, the cyclic-life performance and rate capability were improved. However, heavier coatings (5 wt.%) on LiNi_1/3Co_1/3Mn_1/3O₂ resulted in a considerable decrease of the discharge capacity and rate capability. The thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂ materials was greatly improved by the 3 wt.% Al₂O₃ coating.     

Preparation and characterization of nanostructured Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> and Sn<Subscript>0.5</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Nanostructured Bi₂Se₃ and Sn_0.5-Bi₂Se₃ were successfully synthesized by hydrothermal coreduction from SnCl₂·H₂O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). Bi₂Se₃ powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size of 100–200 nm and several nanometers in thickness. The major phase of Sn_0.5-Bi₂Se₃ synthesized at 180°C is similar to that of Bi₂Se₃. Sn_0.5-Bi₂Se₃ powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies.     

Performance and capacity fading reason of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/graphite batteries after storing at high temperature

Spinel LiMn₂O₄ was synthesized by a solid-state method. A 204468-size battery was fabricated and stored at 55°C. The structure and morphology of the LiMn₂O₄ cathode were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) technique. Energy dispersive spectroscopy (EDS) was used to analyze the surface component of the carbon anode. The discharge capacities of LiMn₂O₄ stored for 0, 24, 48, and 96 h are 106, 98, 96, and 92 mAh·g⁻¹, respectively. The cyclic performance is improved after storage. The capacity retentions of LiMn₂O₄ stored for 0, 24, 48, and 96 h are 83.8%, 85.8%, 86.9%, and 88.6% after 180 cycles. The intensity of all the LiMn₂O₄ diffraction peaks is weakened. Mn is detected from the carbon electrode when the battery is stored for 96 h. Cyclic voltammograms and electrochemical impedance spectroscopy (EIS) were used to examine the surface state of the electrode after storage. The results show that the resistance and polarization of LiMn₂O₄/electrolyte is increased after storage, which is responsible for the fading of capacity.     

Studies on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> high K gate dielectrics applied in a fully depleted SOI MOSFET

Al₂O₃/ZrO₂/Al₂O₃ gate stacks were prepared on ultrathin SOI (Silicon on insulator) substrates by ultrahigh vacuum electron beam evaporation and post-annealed in N₂ at 450°C for 30 min. Three clear nanolaminate layered structure of Al₂O₃(2.1 nm)/ZrO₂(3.5 nm)/Al₂O₃(2.3 nm) was observed with a high-resolution cross-sectional transmission electron microscope (HR-XTEM). High frequency capacitance voltage (C-V) characteristics of a fully depleted (FD) SOI MOS capacitor at 1 and 5 MHz were studied. The minority carriers determine the high frequency C-V properties, which is opposite to the case of bulk MOS capacitors. The series resistance of the SOI substrate is found to be the determinant factor of the high frequency characteristics of FD SOI MOS capacitors. This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24≈27, 2003.     

Chemical state and ultra-fine structure analysis of biocompatible TiO<Subscript>2</Subscript> nanotube-type oxide film formed on titanium substrate

TiO₂ nanotube-type oxide film on Ti substrate has been fabricated using an electrochemical method, and the chemical bonding state, ultra-fine structures, and surface characteristics of the TiO₂ nanotube layer have been investigated. The formation and growth of a self-organized nanotube layer can be achieved directly by anodization in NH₄-containing electrolytes. The diameter, length, and wall thickness of the nanotube are significantly affected by anodizing conditions such as applied voltage, current density, and anodizing time. The length limiting factor of nanotube growth was found to be the diffusion of ionic species in the electrolyte. XRD investigations revealed that annealed nanotubes have anatase and rutile structure, and some Ti-peaks from the Ti substrate were observed. From the compositional analysis of TiO₂ nanotubes layer using Energy Dispersive Spectroscopy (EDS), Ti, O, and P elements were obtained in the wall nanotube layer. For incorporated P-containing in the TiO₂ nanotube layer, various chemical states were presented, which were revealed mostly in the forms of H₂PO₄, HPO₄ ^2-, and PO₄ ^3-.     

Structure and electric property comparison between Ge nanoclusters embedded in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript>

Metal-insulator-semiconductor (MIS) structures containing Ge nanocrystals embedded in both Al₂O₃ and ZrO₂/Al₂O₃ are fabricated by an ultra-high vacuum electron-beam evaporation method. Secondary ion mass spectroscopy (SIMS) results indicate that Ge embedded in Al₂O₃ diffuses towards the surface of the Al₂O₃ layer after annealing at 800°C in N₂ ambient for 30 min. Ge embedded in ZrO₂/Al₂O₃ is stable, thus inducing less leakage current. Capacitance voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by hysteresis in the C-V curves in the Al₂O₃/Ge+Al₂O₃/Al₂O₃ and ZrO₂/Ge+Al₂O₃/Al₂O₃ samples. This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24–27, 2003.     

Electromagnetic wave absorbing properties of Fe<Subscript>73</Subscript>Si<Subscript>16</Subscript>B<Subscript>7</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> base P/M sheets mixed with dielectric fine particles

Fe-based nanocrystalline powder sheets with dielectric TiO₂ powder additives were investigated to improve the characteristics of electromagnetic (EM) wave absorption. The amorphous ribbons of Fe₇₃Si₁₆B₇Nb₃Cu₁ (at.%) alloys were prepared by a planar flow casting (PFC) process, and the ribbons were pulverized using an attrition mill. Fe-based flake powder crystallized at 550°C for 1h was mixed with a nano-sized and a micro-sized TiO₂ powder. The powder mixtures were then tape-cast with binders to become EM wave-absorbing sheets. The absorbing properties of the fabricated sheet sample, such as complex permittivity and permeability, were measured by a network analyzer. The properties of EM wave absorption improved with the increase of TiO₂ powder in the mixture. The mixture with micro-sized TiO₂ powder was a little more effective in causing power loss of EM waves than the mixture with nano-sized TiO₂ powder.     

Preparation and properties of a nano TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> composite superparamagnetic photocatalyst

Nano TiO₂/Fe₃O₄ composite particles with different molar ratios of TiO₂ to Fe₃O₄ were prepared via sol-gel method. X-ray diffraction, transmission electron microscopy, and vibration sample magnetometry were used to characterize the TiO₂/Fe₃O₄ particles. The photocatalytic activity of the particles was tested by degrading methyl blue solution under UV illumination (254 nm). The results indicate that with the content of TiO₂ increasing, the photocatalytic activity of the composite particles enhances, while the magnetism of the particles decreases. When the molar ratio of TiO₂ to Fe₃O₄ is about 8, both the photocatalytic activity and magnetism of the TiO₂/Fe₃O₄ particles are relatively high, and their photocatalytic activity remains well after repeated use.     

Sol-gel preparation and characterization of Li1.3Al0.3Ti1.7（PO4）3 sintered with flux of LiBO2

Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered with different mole fractions of LiBO₂ were prepared by sol-gel method. The structural identification, surface morphology, ionic conductivity, and activation energy of the pellets were studied by X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The results show that all the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered with different mole fractions of LiBO₂ have similar X-ray diffraction patterns. The sintered pellet becomes denser and the boundary and corner of the particles become illegible with the increase of LiBO₂. Among the Li_1.3Al_0.3Ti_1.7(PO₃)₄ pellets sintered with different mole fractions of LiBO₂, the one sintered with 1 mol% LiBO₂ shows the highest ionic conductivity of 3.95×10⁻⁴ S.cm⁻¹ and the lowest activation energy of 0.2469 eV.     

HVOF-Sprayed Coatings Engineered from Mixtures of Nanostructured and Submicron Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> Powders: An Enhanced Wear Performance

In previous studies, it has been demonstrated that nanostructured Al₂O₃-13 wt.%TiO₂ coatings deposited via air plasma spray (APS) exhibit higher wear resistance when compared to that of conventional coatings. This study aimed to verify if high-velocity oxy-fuel (HVOF)-sprayed Al₂O₃-13 wt.%TiO₂ coatings produced using hybrid (nano + submicron) powders could improve even further the already recognized good wear properties of the APS nanostructured coatings. According to the abrasion test results (ASTM G 64), there was an improvement in wear performance by a factor of 8 for the HVOF-sprayed hybrid coating as compared to the best performing APS conventional coating. When comparing both hybrid and conventional HVOF-sprayed coatings, there was an improvement in wear performance by a factor of 4 when using the hybrid material. The results show a significant antiwear improvement provided by the hybrid material. Scanning electron microscopy (SEM) at low/high magnifications showed the distinctive microstructure of the HVOF-sprayed hybrid coating, which helps to explain its excellent wear performance. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Effect of Mn on the mechanical properties and microstructure of reaction sintered Mo<Subscript>2</Subscript>NiB<Subscript>2</Subscript> boride-based cermets

This paper focused on the effects of Mn addition from 0 to 10wt% on the mechanical properties and microstructure of V added Mo₂NiB₂ based model cermets. Transverse rupture strength of the cermets increased with increasing Mn content and showed a maximum value of 3.5 GPa at 2.5 wt.%Mn, and then decreased with further increasing Mn content. Hardness increased monotonically from 86.4R_A up to 10wt%Mn. The high TRS at 2.5 wt.%Mn was attributed to size refinement and homogeneous distribution of Mo₂NiB₂ complex boride resulting from Mn addition. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Interdiffusion in <Emphasis Type="Italic">L</Emphasis>1<Subscript>2</Subscript>-Ni<Subscript>3</Subscript>Al Alloyed with Re

Ternary interdiffusion in L1₂-Ni₃Al with ternary alloying addition of Re was investigated at 1473 K using solid-to-solid diffusion couples. Interdiffusion flux of Ni, Al, and Re were directly calculated from experimental concentration profiles and integrated for the determination of average ternary interdiffusion coefficients. The magnitude of main interdiffusion coefficients and was determined to be much larger than that of the main interdiffusion coefficient A moderate tendency for Re to substitute for Al sites was reflected by its influence on interdiffusion of Al, quantified by large and positive coefficients. Similar trends were observed from ternary interdiffusion coefficients determined by Boltzmann-Matano analysis. Profiles of concentrations and interdiffusion fluxes were also examined to estimate binary interdiffusion coefficients in Ni₃Al, and tracer diffusion coefficients of Re (5.4 × 10⁻¹⁶ ± 2.3 × 10⁻¹⁶ m²/s) in Ni₃Al.     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.