Dong-Yeon Won

Formation of BaCeO 3 and its influence on microstructure of sintered/melt-textured Y-Ba-Cu-O oxides with CeO 2 addition

Formation of BaCeO[sub 3] and its effects on microstructure were studied in sintered/melt-textured Y--Ba--Cu--O oxides containing 5 wt.% CeO[sub 2] and various amounts of Y[sub 2]Ba[sub 1]Cu[sub 1]O[sub 5]. The added CeO[sub 2] was converted to fine particles of BaCeO[sub 3] near 930 [degree]C which is the conventional sintering temperature for Y--Ba--Cu--O. Y[sub 2]Ba[sub 1]Cu[sub 1]O[sub 5] and CuO are formed as by-products of the reaction between CeO[sub 2] and Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7[minus]] [sub [ital y]] phase. The CeO[sub 2] addition reduced the particle size of Y[sub 2]B[sub 1]Cu[sub 1]O[sub 5] which was trapped in the Y[sub 1]Ba[sub 2]Cu[sup 3]O[sub 7[minus]][sub [ital y]] matrix after the melt-texture growth. During the peritectic decomposition stage of Y[sub 1]Ba[sub 2]Cu[sub 3]O[sub 7[minus]][sub [ital y]] phase into Y[sub 2]B[sub 1]Cu[sub 1]O[sub 5] and liquid phase, the morphology of the decomposed Y[sub 2]Ba[sub 1]Cu[sub 1]O[sub 5] was changed from a blocky shape in the undoped sample to an acicular shape of high anisotropy in the CeO[sub 2]-added sample. The formation of the highly anisotropic Y[sub 2]Ba[sub 1]Cu[sub 1]O[sub 5] particles appears to be responsible for the refinement of Y[sub 2]Ba[sub 1]Cu[sub 1]O[sub 5] particle after the melt-texture processing.

Microstructure, microhardness, and superconductivity of CeO2-added Y–Ba–Cu–O superconductors

The CeO 2 -added Y–Ba–Cu–O oxides were prepared by two different processes, the conventional solid-state reaction process and the partial melt process using powders, to examine the effect of the dopant on microstructure, microhardness, and superconductivity. In the solid-state reacted sample, most of the added CeO 2 was converted to a form of BaCeO 3 , but some might enter into the 1-2-3 phase, resulting in the orthorhombic-to-tetragonal phase transition that accompanied the disappearance of twin structure in 1-2-3 grains. In the partially melted sample, however, the phase change was not observed up to 5 wt. % of CeO 2 . All the added CeO 2 in these samples was consumed to form only BaCeO 3 which was finely dispersed in large 1-2-3 grains during the peritectic reaction stage. The zero resistance temperature (T c ) of the solid-state reacted sample gradually decreased with increasing CeO 2 content due to the phase change and the formation of BaCeO 3 , whereas the T c of the partially melted sample was nearly constant regardless of CeO 2 content up to 5 wt. %, owing to the separation of the second phase from the 1-2-3 superconducting phase. Microhardness of the partially melted sample increased with increasing CeO 2 content. The strengthening effect appears to come from the composite system where the fine BaCeO 3 particles are dispersed in a 1-2-3 matrix.

Entrapment of Ba-Cu-O liquid phase during growth of a Y1Ba2Cu3O7−y domain

Abstract Entrapment of Ba-Cu-O liquid phase during the growth of a 123 domain was investigated in the melt-textured Y-Ba-Cu-O oxide. From the microstructural examination of the growth front of the 123 domain, it is found that liquid phase is entrapped in the channels between adjacent 123 platelets formed ahead of the 123 domain, owing to the anisotropic growth of the 123 platelet, the difference between the growth rate of the 123 platelet and the dissolution rate of 211 in the liquid phase, and the inhomogeneous distribution of 211 particles at the peritectic reaction front. Dissolution of 211 particles in the reaction region, which supplies an yttrium source to the liquid channels, allows the entrapped liquid phase to solidify to 123 phase. After the peritectic reaction, the liquid channels turn into plate boundaries containing residual liquid phase as evidence of the entrapment. Isolation of the entrapped liquid phase from the yttrium source (211 particles) by the solidified 123 phase appears to be responsible for the presence of the residual liquid phase.

Effect of Neutron Irradiation on Tc of Pb-Doped BiSrCaCuO Superconductor

A Pb doped BiSrCaCuO superconductor was irradiated in a TRIGA MARK III reactor up to a neutron fluence of 7.6×1017 n/cm2. The measured superconducting transition temperature (Tc) after irradiation was decreased to 92.5 K from nonirradiated data of 102 K. The fractional decrease of the Tc was compared with results fon other superconducting materials. Some recovery of irradiation-induced Tc decrease was observed.

Metal oxide (MeO=CdO, CeO2, Cr2O3, Nd2O3, Sb2O3, UO2 and ZrO2) addition in YBaCuO prepared by partial melt processing

On examine les effets des oxydes de Cd, Ce, Cr, Nd, Sb, U et Zr sur la supraconductivite de YBa 2 Cu 3 O 7-δ prepare par fusion partielle

Preparation of YBaCuO Film on a MgO Substrate by Chemical Vapor Deposition at 650°C

YBaCuO films were prepared on a MgO(100) single-crystal substate at 650°C by a chemical vapor deposition method. The films were fabricated at various oxygen partial pressures of 0.516 Torr, 0.121 Torr, 0.0126 Torr and 0.009 Torr. Superconductivity above liquid nitrogen temperature (Tc,0=87 K and Tc,onset=91 K) was obtained for the film prepared at 0.0126 Torr. Jc(77 K, 0 T) was measured as 3×104 A/cm2. A two-dimensionally well-aligned microstructure was observed for the film prepared at 0.0126 Torr.

Pressure Dependence of the Formation of YBaCuO Films by Chemical Vapor Deposition

YBaCuO films were prepared on MgO(100) single-crystal substrates at 850°C under various pressures by the chemical vapor deposition method. The films showed superconductivity above liquid nitrogen temperature (Tc,0=81~84 K). Faster growth of films that accompanied the formation of a porous microstructure was observed as the pressure was reduced.

Structure and Superconducting Properties of the Bi1.4Pb0.6Sr4-xCaxCu3.8Oy System (0≤x≤4)

Samples of Bi1.4Pb0.6Sr4-xCaxCu3.8Oy (0≤x≤4) were prepared by sintering at various temperatures (805°C–870°C). The structure and superconducting properties of Bi1.4Pb0.6Sr4-xCaxCu3.8Oy were altered by varying the Sr/Ca ratio. For x=0 and 0.5, the c parameter of the unit cell was ~25 A and no superconductivity was observed down to 77 K. For x=1 and 1.5, the c parameter was ~31 A, and Tc end and Tc onset were 81 K and ~90 K, respectively. For x=2 and 2.5, the c parameter was ~37 A and Tc end and Tc onset were 91 K and ~105 K, respectively. For x=3 and 3.5, the c parameter was ~31 A and Tc onset was 80 K, but zero resistivity did not appear down to 77 K. On the basis of these results, the structure and superconductivity of the Pb-doped BiSrCaCuO system are discussed.

Alternating Magnetic Field Shielding of YBCO Tubes in Static Field

The alternating magnetic field shielding efficiency of a YBCO tube was measured in a static field of up to 1 kG, bearing the possibility of its application as a field regulator in mind. The shielding efficiency is higher when the sample is field-cooled than when it is zero-field-cooled, as predicted by the critical state model. In the case of field cooling, the tube still shields about 25% of ac field of 1 kHz even in 500 G dc field. Shielding efficiency monotonously increases with increasing frequency from 10 Hz to 1 kHz.

Preparation of YbBaCuO Film on Various Substrates by Chemical Vapor Deposition at 650°C

High Tc YbBaCuO film(Tc,0 gt 80K) was successfully prepared on various substrates by CVD method using molecular oxygen as an oxidant. The deposited 123 phase showed c-axis oriented structure with a large c-axis lattice parameter with c = 11.706 ~ 11.826A. It was observed that the formation of 123 phase accompanied 132 phase as well as BaCuO and CuO. It is very noticeable that Yb2O3 was also deposited with 123 phase in YbBaCuO system.