Weir-Mirn Hurng

Formation mechanism study of REBa2Cu4O8+δ (RE=Y and Dy) accelerated by nitric acid

An accelerated formation of REBa2Cu4O8+δ (RE=Y and Dy) was observed as a suitable amount of nitric acid was added. This provides an excellent route for preparing high‐ purity REBa2Cu4O8+δ in ∼ 30 h. X‐ray diffraction and thermal analyses (TGA/DTA) were conducted to reveal the formation mechanism. The addition of nitric acid did not change the reaction routes but formed more Ba2Cu3O5 which might play an important role for the formation of REBa2Cu4O8+δ. Magnetization data confirmed the Tc’s of 80 and 75 K for as‐prepared Y‐124 and Dy‐124, respectively.

Studies of electrochemical properties of lithium cobalt oxide

The electrochemical characteristics of high-temperature (HT) LiCoO2 (900 °C) and low-temperature (LT) LiCoO2 (450 °C) were studied. From cyclic voltammetry results, lithium intercalating into LT-LiCoO2 generates two current peaks at 3.8 and 3.3 V, respectively, which is contrast to the intercalation of lithium into HT-LiCoO2. The resistance of lithium extraction is smaller than that of lithium insertion. The diffusion coefficients of Li+ ions in LiCoO2 have an order of 109− cm2/s.

Studies of LiNiO2 in lithium-ion batteries

Abstract Lithium nickel oxide, LiNiO2, with different physical properties including crystalline phase, CV curve and particle-size distribution were characterized. LiNiO2 with spherical agglomerates were constructed by ∼0.1 μm fine particles and their cycling stability showed to depend on the particle-size distribution when compared at different end-voltage and cycling rates.

Performance study of the LiCoO2/graphite system

Abstract Lithium-ion AA battery with LiCoO 2 as the cathode and graphite-like carbon as the anode is developed. Performance versus modification of the anode such as copper-foil type, additive, paste-mixing method, material treatment, and electrode treatment, etc., is studied. Finally, an AA battery with 500 mAh capacity and good cycle life is developed.

Cokes as negative electrodes in secondary batteries

The lithium intercalated carbons (LixC6) have replaced the metallic lithium negative electrodes in secondary lithium batteries. In order to improve high energy density and long cycle life, it is necessary to find those carbonaceous materials that have an excellent lithium intercalation and de-intercalation capacity. In this work, the electrochemical behaviour of various cokes in ethylene carbonate (EC) and dimethyl carbonate (DMC) electrolyte were investigated by charge and discharge cycling processes and cyclic voltammetry technique. The petroleum coke (C342) has the highest capacity during cycling and the lowest irreversible capacity loss during the first cycle. Cyclic voltammetry revealed that the cycle efficiencies of three cokes are very high.

Synthesis of the three Cu-O layered Tl-(Pb,Bi)-Sr-Ca-Cu-O compound

A three Cu-O layered superconducting compound in the Tl-(Pb,Bi)-Sr-Ca-Cu-O system has been prepared by different processes. These include the use of excess Ca and Cu for off-stoichiometric composition, and the increase in Ca/Sr ratio for modified stoichiometric composition. A nearly single phase of 1223 superconductor can be obtained within three hours of heat treatment using the modified stoichiometric composition, whereas the intermediate phase (Ca,Sr)2CuO3 was remarkably accompanied in other synthetic processes. Observations were also corroborated by X-ray diffraction and magnetization measurements.

Structure and thermal behavior studies of ZrO2 treated by different concentrations of sulfuric acid

Abstract The acid strength of ZrO2 was enhanced after it was treated with H2SO4 or other SOx sources. This research investigated how this H2SO4 treatment affects the ZrO2 material from the structural point of view. A series of ZrO2 samples. which were prepared through the solution method with different sulfuric acid concentrations, were studied by X-ray diffraction and thermal analyses to reveal the correlation between the physical properties of the samples and the concentration of the acid. XRD results indicated that the yield of ZrO2 with tetragonal form declined with the concentration of the acid and vanished as its concentration became higher than 1N. Also, the crystallinity of the samples became poor with the increase of the concentration of the acid. The thermal analysis showed that the amounts of acid (or SO2) absorbed by the samples were proportional to the concentration of sulfuric acid.

Preparation of YBCO superconductor thin film by spin-coating method with metal-organic precursors

YBCO thin film was prepared by the spin-coating method with metal-organic precursors. The precursors were synthesized by reacting metal acetates with 2-ethylhexanic acid or by reacting metal halides with ammonium 2-ethylhexanate directly. After proper heat treatments, YBCO film with Tc, onset = 80 K and Tc,zero = 77 K was obtained. SEM studies of a sample prepared at 990 °C showed the presence of CuO and Ba2YCuO5 (211 phase). This suggested the transient presence of a liquid phase which had been observed in preparing YBCO bulk material by the melt-texture method before the formation of YBCO phase. Furthermore, many voids were observed in the as-obtained film. These might be the origin of the relatively low Tc,zero, temperature.

X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF (TL0.5PB0.5)SR2(CA1-XTHX)CU2OY SYSTEM FOR X = 0.0 - 0.3

Abstract To reveal the correlation between the Tc temperatures and the hole concentration in p-type cuprates superconductors, a series of samples of (Tl0.5Pb0.5)Sr2(Ca1-xThx)Cu2Oy (x = 0.0 − 0.3) were prepared and investigated by the X-ray photoelectron spectroscopy. The core-level of Cu did not show consistent variation while a slight shifting of Tl 4f 7 2 , 5 2 peaked up to high binding energy as Th dopant increased. This might be resulted from the decrease of the hole concentration in Tl-O layer. The Sr core-level spectra demonstrated an evident and consistent variation which could be attributed to two lattice sites available for Sr atoms and the decrease of Ca atoms. Our results indicated that the Tl-O layer might act as “hole reservoir”, which had been already suggested by the band structure calculation.

The application of gradual releasing precipitant method in the preparation of YBCO superconducting powder

Abstract The oxalate generated from sonication aided hydrolysis of diethyl oxalate could offer a way to produce high quality YBCO superconducting powder. The mean particle size of 1.1±0.6 μm powder providing good property for sintering and it will have an excellent opportunity for mass production.