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Er and Mg co-doped LiNbO₃ crystal fibers with a melt concentration of 1, 3 ㏖% MgO and 0.6 ㏖% Er₂O₃ have been grown by the micro-pulling-down (μ-PD) method to study the Er and Mg incorporation into the LiNbO₃ matrix. The structure as determined from XRD diffraction is hexagonal, with lattice constants a=5.1570, c=13.8595 Å (1 ㏖% MgO and 0.6 ㏖% Er₂O₃ co-doped crystal), and a=5.1587, c=13.8578 Å (3 ㏖% MgO and 0.6 ㏖% Er₂O₃ co-doped crystal). The structural similarities between the Er:Mg:LiNbO₃ and the well-studied LiNbO₃, Er:LiNbO₃ are discussed.

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Electrical transport and magnetoresistance characteristics were investigated for sintered Fe₃O₄-xFe (x = 0, 10, 20 wt.%) specimens. For composition dependence of Fe₃O₄-xFe specimens sintered at 500℃, the largest MR of 3.3% at 10 kOe was obtained in Fe₃O₄-10Fe specimen. It was found that this enhanced MR appears together with the appropriate excess resistance, which regarded as tunneling barrier, in the interparticle of Fe₃O₄. It indicates that the enhanced MR ratio arises from the spin dependent tunneling effect and can be explained with increased interparticle contacts. On the other hand, for the sintering temperature dependence of Fe₃O₄-xFe samples, the MR ratios decrease with the increased sintering temperature. The decreased MR ratios for Fe₃O₄-xFe may be associated with the decreased resistance due to the growth of Fe₃O₄ particles in Fe₃O₄ specimen and inadequately increased tunneling barrier of Fe_(l-x)O particles in Fe₃O₄-10, 20Fe specimens.

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The structural and magnetic properties of CoNbZr/SiO₂ multilayer films were investigated. Effects of the surface roughness of SiO₂ layers on the properties of CoNbZr/SiO₂ multilayer films were analyzed. The minimum coercivity 3.73 Oe and the maximum permeability at 100 ㎒ of 1783 was observed in [Co_(89.3)Nb_(6.1)Zr_(4.6) 100 ㎚ / SiO₂ 8 ㎚] multilayer films deposited at 130 W and 2 mTorr for CoNbZr films and 200 W and 2 mTorr(Ar/H₂ 20%) for SiO₂ films. When sputtering gas pressure for SiO₂ films increased from 2 mTorr to 6 mTorr, the optimum thickness of SiO₂ layers increased from 10 ㎚ to 25 ㎚. It is thought that degradation of efficiency of insulation was resulted from increase of surface roughness of SiO₂ layers. Futhermore, by the addition of 20% H₂ gas to sputtering gas, the surface roughness of SiO₂ layers decreased from 7.4 Å to 2.14 Å so that soft magnetic properties were improved. When multilayer was annealed for 90 min at 300℃, we obtained anisotropy field of 14 Oe, permeability at 100 ㎒ of 2800. That is considered that the major factor of annealing effect is both reduction of defects and increase of anisotropy in initial stage, but reduction of defects only in later stage.

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The effects of surface treatments on the energy band bending below the surface of p-type GaN were studied using synchrotron radiation photoemission spectroscopy. It was found that surface oxides composed of Ga and O, namely GaO_x, were formed during the high temperature processes, the growth ($gt;900℃) and the activation ($gt;700℃), causing the production of Ga vacancies, V_(Ga), below the oxides. The aqua regia treatment was effective in removing GaO_x on p-type GaN, leading to the Fermi level pinning at the energy levels of V_(Ga) locating near the valence band edge. This causes the decrease of barrier height for the transport of holes, resulting in the reduction of the contact resistivity by four orders of magnitude.

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The isothermal solidification behaviors and single crystallization in bonded interlayer of a Ni-base single crystal superalloy, CMSX-2, during transient liquid phase (TLP) bonding were investigated employing MBF-80 and F-24 insert metals. TLP bonding of CMSX-2 was carried out at 1373∼1548K for 0∼19.6 ks in vacuum and the $lt;001$gt; orientation of each test specimen was always aligned perpendicular to the joint interface. The eutectic width diminished linearly with the square root of holding time during isothermal solidification. Electron back scattering patterns of completed joints revealed that the bonded layer had single crystallized during the TLP bonding process and matched the crystallographic orientation of the bonded substrates. It follows that epitaxial growth of the solid phase occurred from the base metal substrates during isothermal solidification.

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The effect of oxide additives, such as BaO, Li₂O, K₂O and Na₂O in CaO-CaF₂-SiO₂ slags on the equilibrium phosphorus distribution ratios, L_p between molten slags and Fe-C_(sat·)-P melts were studied at 1300℃. The effect of BaO addition on the increase in the L_p is more significant when it is added to the lower basicity slag. The small addition of Li₂O K₂O and Na₂O in CaO-CaF₂-SiO₂ slags significantly increases the L_p. The stability of Li₂O in slag is much higher than K₂O and Na₂O during the dephosphorization reaction. The correlation between the phosphate capacities of slags containing alkali metal oxides does not show the linear relationship with their optical basicities. The alkali metal oxides decrease the activity coefficient of phosphate ions in slag drastically, and thereby increase the dephosphorization capability of CaO based slags.

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The effects of Si content on the microstructures, mechanical properties, oxidation resistance and thermal expansion of ductile cast irons have been studied using optical microscopy, scanning electron microscopy, hardness test, oxidation test, dilatometry, and tensile test. The spherical graphite cast irons are manufactured by horizontal continuous cast process. The volume fraction of pearlite structure in as-cast alloys continuously decreased down to ∼3%Si and reached nearly zero at the above Si content. The hardness and tensile strength of ductile cast iron showed a minimum at ∼3%Si. The result was due to an overlapping effect of matrix strengthening of pearlite structure and solid solution hardening by Si element. The tensile ductility increased continuously as Si content increases from 2.4% to 3.85%. the oxidation rate has a constant value regardless of Si content in the temperature range of 600∼700℃. On the other hand, the oxidation rate decreased with the increase of Si content in the temperature range of 800∼1000℃. Specially, in this temperature range, the oxidation resistance more enhanced at Si content above ∼3.4%. This result directly related to the diminution of Fe₃O₄ type oxide layer. The coefficient of thermal expansion has more larger values at annealed state than as-cast state.

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