Kuan-Zong Fung

Synthesis and characterization of Li1+δMn2−δO4 powders prepared by citric acid gel process

Abstract Li1+δMn2−δO4 were synthesized by citric acid gel process using lithium acetate and manganese acetate as the sources of lithium and manganese. Spinel Li1+δMn2−δO4 had been synthesized at various temperatures from 200 to 500°C and the synthesis mechanism was examined by thermal and structural analysis. Li1+δMn2−δO4 can be synthesized as low as 200°C is attributed to the short distance between lithium and manganese formed in precursor prepared by citric acid gel process . Thus, lithium and manganese could react each other and form the desired compound at low temperatures. The lattice parameter of powders increased with increasing temperature from 8.136 A at 200°C to 8.211 A at 500°C. The specific surface area of sample calcined at 200°C was 160 m2/g and deceased with calcination temperature increasing. From the SEM studies, the powder prepared at 200°C showed porous structure due to the liberation of CO2 and H2O from the decomposition of organic material. The particle size of powder calcined at 300°C for 24 h in the range of 60 to 85 nm. The powder synthesized by citric acid gel process showed circular shape and did coarsen significantly with the calcination temperature increased.

Fabrication and Characterization of Cu2O Nanorod Arrays and Their Electrochemical Performance in Li-Ion Batteries

This study is an investigation of the electrochemical performance of Cu 2 O nanorods in Li ion battery application. The templatemediated electroplating was applied to fabricate Cu 2 O nanorod arrays. The morphological observation shows that the nanorods with 60 nm diam and 450 nm length were grown perpendicularly to the substrate. The cyclic voltammetry sweeping indicates a reversible electrochemical reactivity between Cu 2 O nanorods and Li, and cycling tests show that the nanorod arrays exhibit a capacity of 330 mAh/g after 100 cycles. The high capacity and good cycle retention imply that Cu 2 O nanorods are a candidate anode material for rechargeable power source.

X-ray photoelectron spectroscopic and secondary ion mass spectroscopic examinations of metallic-lithium-activated donor doping process on La0.56Li0.33TiO3 surface at room temperature

The donor doping process at the interface between the cation-deficient La0.56Li0.33TiO3 and lithium was elucidated by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). XPS revealed a chemical shift (∼1.48eV) from the main peak of Ti4+ 2p3∕2 toward the low energy side, due to the conversion of 12% Ti4+ to Ti3+. The SIMS analysis indicates that a local electric field was responsible for the insertion of oxidized Li+6 isotope ions. The doping with Ti3+ donors, accompanying the insertion of Li+ ions into cation vacancies of La0.56Li0.33TiO3, yields the n-type semiconducting characteristics at room temperature.

Mechanism of the interfacial reaction between cation-deficient La0.56Li0.33TiO3 and metallic lithium at room temperature

We used x-ray diffractometry (XRD), x-ray photoelectron spectrometry (XPS), and secondary-ion mass spectrometry (SIMS) to investigate the mechanism of the interfacial room-temperature (RT) chemical reaction between cation-deficient La 0.56 Li 0.33 TiO 3 solid electrolytes and metallic lithium anodes in all-solid-state lithium batteries. A stoichiometric mixture of La 2 O 3 , Li 2 CO 3 , and TiO 2 powders was calcined at 1250 °C for 8 h to obtain a single perovskite structure of La 0.56 Li 0.33 TiO 3 . When this La 0.56 Li 0.33 TiO 3 sample and lithium were placed in contact at room temperature for 24 h, the phase of the La 0.56 Li 0.33 TiO 3 remained unchanged. The XPS results indicate that 12% of the tetravalent Ti 4+ ions were converted into trivalent Ti 3+ ions. The valence conversion and degree of conversion were limited by the structural rigidity of the host crystal. Our SIMS analysis suggests the existence of a local electric field near the contact surface and indicates that the 6 Li + isotope ions were inserted into the specimen through the effect of this field. The change in the electrical properties of La 0.56 Li 0.33 TiO 3 supports this mechanism for the interfacial reaction. The ionic conductivities of the grain and total grain boundary decreased and increased, respectively, after the insertion of Li + , and the total electronic conductivity increased as a result of the presence of intervalence electron hopping between mixed Ti 3+ /Ti 4+ states. The mechanism of the lithium-activated RT interfacial reaction is associated with the reduction of Ti 4+ transition metal ions from tetravalent to trivalent states and the local-electric-field-induced Li + insertion into La 3+ /Li + -site vacancies of La 0.56 Li 0.33 TiO 3 .

Fabrication of δ-Bi[sub 2]O[sub 3] Nanowires

© The Electrochemical Society, Inc. [2005]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in [Electrochemical Solid-State Letters, Vol.8, No.4, pp.A204-A206].”

Preparation and Characterization of Solid Electrolytes Based on TiP2O7 Pyrophosphate

The Li4xTi1-xP2O7 (x = 0, 0.06, 0.1, 0.2) powders have been synthesized by the solid state reaction and their ceramics have been sintered. The Li4xTi1-xP2O7 (x = 0.06, 0.1, 0.2) compounds have cubic superstructure 3×3×3 (space group Pa-3), which is also typical for TiP2O7 pyrophosphate. The electrical properties of the ceramics were investigated in the frequency range of 10 to 3·109 Hz and temperature interval of 400–720 K by impedance spectroscopy. The relaxation dispersion region in the conductivity and dielectric permittivitty spectra of Li4xTi1-xP2O7 (x = 0, 0.06, 0.1, 0.2) ceramics was found.

Fabrication of δ-Bi2O3 Nanowires

© The Electrochemical Society, Inc. [2005]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in [Electrochemical Solid-State Letters, Vol.8, No.4, pp.A204-A206].”

One-pot synthesis of size and shape controlled copper nanostructures in aqueous media and their application for fast catalytic degradation of organic dyes

The present investigation reports the novel chemical reduction synthesis of air resistant copper nanostructures (particles or rods) at a high concentration (up to 0.3 M) with controlled size and shape in an aqueous media. These syntheses accomplished high yields using sodium borohydride as a reducing agent, L-(+)-tartaric acid as a new surfactant and antioxidant, and polyvinylpyrrolidone (PVP) as a capping agent. The input of extra inert gases was not necessary and this method is very simple and green. Some reaction parameters, such as amount of reactants or surfactant, pH, reaction time or rate and amount of reduction reagent, were effective for control in the size and shape of the nanoparticles. Furthermore, colloidal copper nanoparticles effectively catalytically degrade methyl orange. The synthesis method reported in this work might be useful for the large-scale production of Cu nanoparticles.

Effect of Temperature on Phase Transition of Ni-Co Oxide and its Application on Optoelectronics

Ni-Co thin films were prepared on glass substrate by RF magnetron sputtering technique. Post-deposition annealing of Ni-Co film in oxygen atmosphere was found to improve film structure and electrical characteristics. The correlation between annealing conditions and the physical structure of the films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis-NIR spectrophotometer. The lowest resistivity was observed after annealing a sputter-deposited Ni-Co film at 600 °C for 5h. The transmittance showed more than 85% in the infrared range. The preferred annealing condition has been found to improve Ni-Co film characteristics for transparent conducting material applications.Keywords: Ni-Co film, annealing, phase transition

Fabrication of delta-Bi2O3 nanowires

© The Electrochemical Society, Inc. [2005]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in [Electrochemical Solid-State Letters, Vol.8, No.4, pp.A204-A206].”