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Based on the present situation of microelectrode machining, electrochemical micromachining (EMM) was regarded as one of the most advanced micromachining techniques. The machining technology of microelectrode was put forward by the method of high frequency short pulses in electrochemical machining (ECM). The shaping principle of microelectrode was analyzed. Then a suitable EMM system was designed. Through the research of technologic experiments, a microelectrode is fabricated with diameter 30μm and top radius 100nm, which is made of tungsten filament. This could provide microelectrode for further electro-machining or micro probe for scanning probe microscopy. The surface property and the machining capability of the microelectrode are compared with the microelectrode fabricated by Electrical Discharge Machining (EDM) at last. The superiority of the microelectrode fabricated by ECM is showed off fully. Further research on EMM will provide more opportunities for ECM in the field of micromachining.

Proposed a new process technology of micro electrical discharge machining (EDM) beyond the traditional EDM concept. This method can deposit the brass wire tool electrode on the workpiece surface by pulse discharges between anode and cathode in air. At first, the basic machining parameters, which realize micro electrical discharge deposition, are prejudged according to the discharge phenomena in air and EDM basic theory. Afterwards, a lot of experiments were carried on an ordinary sinking-EDM machine tool. The results of experiments show that wire tool electrode materials, brass, can be deposited on steel workpiece surface. The diameter of micro fabricated cylinders is 100–240 microns, and the height is 1000–7350 microns. On some special machining parameters, a micro spiral structure can be deposited also, which is 100 micron in thread diameter and more than ten cycles. Excepting lots of experiments, the structure and properties of deposited substance were analyzed by SEM, spectroscopy analysis and micro hardness meter and so on. The results of analyzing the deposited cylinders show that the structure is multi-layer, which is beneficial for the further study of 3D scanning machining. The hardness is a little higher than the original metal. In this depositing process, element Zn of tool electrode is almost oxidized to ZnO. Element Cu is not oxidized, existing as solid Cu. Because the reactivity of Cu is weaker than that of Zn.Copyright © 2005 by ASME

Temperature dependent X-ray diffraction is carried out in order to study lattice vibrational behavior in Bi1.6Pb0.4Sr2Ca2Cu3−xFexOy (x=0 and 0.08 respectively). The study focuses attention on the (002) diffraction peak. The lattice parameters and the anomalous behavior of the intensity of the (002) peak show the existence of a lattice softening effect at approximately 130 and 200 K. The samples with different values of Tc show different vibrational behavior.

Anomalous behavior of the Mossbauer factor for tin impurity atoms in Bi-system Superconductors is found by Mossbauer spectroscopy. This indicates the occurrence of lattice softening above Tc.

X-ray diffraction study was conducted over the range from 77K to room temperature about high-Tc superconducting phase Bi-system. Temperature dependent intensity of (002) peak and lattice parameter show evidence of lattice vibrations softening, which occurs at about 130K and 210K.

A joint experimental and theoretical investigation is performed for Ba–Sn–Ga type-I and type-VIII clathrates. The type-I sample shows a semiconductor characteristic which is accords with the first principle simulation. The type-I clathrate follows Zintl-like behaviour and the semiconducting gap is about 0.6 eV which is agreement with measurement. For the type-VIII clathrate, the simulation shows that a complicated band structure around Fermi level. For the density of states, a peak appears in the fundamental gap, which corresponds to hybridization of Ba bonding orbitals and Sn(Ga) network. A superconducting transition at T C =4 K is observed, which is close to the T C of Sn. An alternative explanation is superconductivity in type-VIII sample arises from increase of electronic density of states around Fermi level E F in the BCS theoretical frame.

The dynamic studies of the hyperfine interactions and the lattice vibrational behavior are performed by means of temperature-dependent Mossbauer spectroscopy and X-ray diffraction on Bi-2223 superconducting phases. The Mossbauer studies show the anomalous lattice effect taking place above, but relatively close to, the transition temperature. The anomalous decrease of the isomer shift reveal the delocalization effect of d-electrons.

There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46−xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC = 5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x = 6 sample Ba8Si40Al6, the superconducting transition was observed down to TC = 4.7 K which pointed to a strong suppression of superconductivity with increasing Al content as ...

Samples with different fractions of structural modulation were synthesized in order to study the effect of a defective modulated structure on the critical temperature T c of Hg-1234. Electron microscopy revealed the existence of modulated and unmodulated Hg-1234 structures in these samples. Measurements of critical temperature T c on these samples revealed that the structural modulation significantly suppresses the T c . For the Hg-1234 sample without the structural modulation, the T c was found to be close to the highest T c for the Hg-1223 phase.

The structural and physical properties of LiMn2-xFexO4 (x = 0 to 0.5) were investigated. Contrasting LiMn2O4 with LiMn1.5Fe0.5O4, we observed a remarkable difference in the magnetic frustration. The LiMn2O4 sample has a magnetic ordering transition at 61 K while Fe-doped LiMn1.5Fe0.5O4 has an antiferromagnetic ordering transition with a Neel temperature at TN = 34 K. Our result showed a larger value of the frustration index (f=| w|/TC) for pure LiMn2O4 than for LiMn1.5Fe0.5O4. Fe-doping results in a decrease in the degree of frustration. Fe dopants occupying positions of Mn ion can break the original moment equilibrium so as to suppress the magnetic frustration in LiMn2O4.

Transition metal compounds with two-dimensional triangular lattice, such as LiVO2, are of particular interest, because they exhibit peculiar structural and magnetic behavior involving the frustration present in these oxides. An orbital ordering transition occurs near 500 K, which leads to a suppression of magnetic moment below the phase transition temperature Tt. We synthesized a series of Mg-doped LiVO2 single-phase samples and reported their structural and magnetic properties. The samples were characterized by x-ray diffraction, scanning electron microscope, differential scanning calorimetry, electrical resistivity, magnetic susceptibility, and specific heat measurement. For Mg-doped samples Li1−xMgxVO2 (x=0, 0.05, 0.10, and 0.15), the structural analysis show that, with increasing x, the lattice constants change monotonously; in the a-b plane, the lattice expands; while in the c-axis direction, the lattice is compressed. Substitution of Li with Mg ions results in the degeneration of two-dimensional cha...

The magnetic properties of (Eu 1-x Y x )Ba 2 Cu 3 O 7−y (x=0 and 0.3) superconductors have been investigated by vibrating sample magnetometry (VSM) from 20 to 90 K and up to 8 T. Hysteresis loops of the Y-doped sample exhibit a strongly developed second peak at higher temperatures. The critical current densities derived from these data were nonmalised to the values at the peak position, J Cp , and analysed as a function of applied field normalised to the peak field. We discuss the experimental results in terms of a stress-field pinning model: The stress-field induced by lattice mismatch provides an effective pinning centre, in addition to the 211 phase precipitates and oxygen vacancies. We further suggest that in the Eu 0.7 Y 0.3 -123 sample, the oxygen-deficient region induced by the stress-field also adds to the pinning, and accounts for the enhancement of the peak effect in the J C -H curves of the Eu 0.7 Y 0.3 -123 superconductor.

In order to investigate the reason of Jc increment in (RE,Y)-123 superconductors, we prepare Eu-doped (Eu x Y 1−x )-123 ceramic samples with different Eu concentration. Positron lifetime and Doppler-broadening spectrum are simultaneously used to investigated the defects (stress field) verse different Eu-substitution. The experimental results support the stress-field pinning mechanism.

The dynamic studies of the hyperfine interactions and the lattice vibrational behavior are performed by means of temperature-dependent Mossbauer spectroscopy on the Bi-, Tl-, and Y-based superconductors, respectively. The temperature-dependent Mossbauer recoil-free factor f show that, above, but relatively close to, the transition temperature, there is an anomalous lattice effect which is related to the softening of phonon vibrational modes for Bi-2223, Tl-1223, and Y-123 superconductors. Moreover, for such three systems, the anomalous decrease of the Mossbauer isomer shift above Tc reveal the delocalization effect of d-electrons. Since the lattice effect is accompanied by d-electron delocalization effect at the almost same temperature region, it is believed that the structural instability involved in phonon softening is strongly interrelated to the change of the electronic states, and the phase separation behavior.

The phonon softening near T c on iron-doped Tl - 1223 phase samples were observed by 57 Fe Mo¨ssbauer measurements at temperatures ranging from 77K to 250K. Simultaneously, the temperature dependence of positron annihilation parameters on an iron-free sample show the anomaly of the electronic behavior in the temperature range from T c to T c +30K.

The variety of intergrowth in the Hg Ba Ca Cu O oxide system was found by the high resolution electron microscope(HREM). A new phase of Hg-2435 was synthesized under high pressure for long time. Another longer period structure of -2223- was also found in such prepared sample. However, these complex intergrowth structures only contain the Hg-1212 and Hg-1223 phases.

The photoemission spectrum was measured on YNi2B2C and was found to be well coincident with calculation except in the vacinity of EF. The DOS peak at EF predicted by band theory has not been detected. The author suggests that the low energy excitation which is responsible for the suppression of DOS at EF, is responsible for the pairing of superconductivity as well.

A excess oxygen model that explains the Fe-doping mechanism in 1223 Tl Ba Ca Cu O superconducting phase is presented. So far the details of the coordination of Fe dopant is not understood completely yet, for Fe dopant substitution in Tl-system cuprate oxide. The similarity in the ionic radii and electronegativity of Cu and Fe lead to the Fe occupying Cu lattice site. However, the difference between the oxidation states of Fe and Cu means that Fe will bring the excess oxygen into lattice to keep the charge balance. We show that, for the evidence of the excess oxygen., the bonding energy of Fe-cluster in Cu O layer reach its minimum when Fe make a shift from the center of Cu O square network. Moreover, under the scheme of effective valence, the calculated value of Fe effective valence is relatively close to that of Mossbauer measurement.

The temperature-dependent Mossbauer study was performed in Fe-doped Bi-2223 phase. The anomalous behaviors of hyperfine interactions have been observed to take place above, but relatively close to, the transition temperature. The anomalous drop of isomer shift and quadrupole splitting show the delocalization effect of d-electron.

The occupied position of Fe in the superconducting phase of Fe-doped YBa2Cu2.8807-x was estimated by point charge model. The Mossbauer spectra were measured in the temperature range from 78 K to 273 K. Lattice softenings were found near 110 and 220 K. The observed variations of hyperfine parameters can be considered tobe related to the lattice softening near 110 K. It is suggested that the lattice softening near 110 K is related to the Peierls instability of the one-dimensional Cu(1)−0 chains.

Samples of YBa2Cu2.88Fe0.12O6+x quenched at different temperatures were investigated by Mossbauer spectroscopy at room temperature. Dynamic measurement on the 950 degrees C quenched sample was also performed between 78 and 300 K. The magnetic splitting corresponding to antiferromagnetism can be observed for the high-temperature ( >850 degrees C) quenched samples, whereas no magnetic splitting occurs for the low-temperature quenched samples. Such results indicate a close relationship between the oxygen concentration and antiferromagnetism. The large value of the hyperfine field implies that the antiferromagnetic interaction is rather strong. For the 950 degrees C quenched sample, the fitted hyperfine field exhibits linear dependence on the temperature (78-300 K). The mechanism leading to antiferromagnetism is discussed.