• Korean Journal of Materials Research
• /
• v.5 no.4
• /
• pp.433-444
• /
• 1995

BaCe$O_{3}$를 첨가하여 용융공정으로 제조한 단결정형 Y$Ba_{2}$$Cu_{3}$$O_{x}$(1-2-3) 초전도체의 온도에 대한 자화특성을 연구하였다. 고상반응법과 용융공정으로 0에서 30wt% BaCe$O_{3}$를 1-2-3 결정내에 미세 분산시켰다. 초전도체의 자화특성은 VSM(vibrating sample magnetometer)을 사용하여 77K, 60K, 40K와 20K, 2 Tesla 자장범위에서 측정하였다. BaCe$O_{3}$를 첨가하지 않은 겨우나 5wt% BaCe$O_{3}$를 첨가한 1-2-3 결정의 경우, 77K, 외부자장이 증가시 자화율 차이가 증가하는 비정상 자화특성이 관찰된다. 측정온도가 60K에서는 제2차 최대점이 나타나는 자장값이 고자장쪽으로 이동한다. 20K와 40K의 저온에서는 비정상자화특성이 2 T의 자장범위까지 관찰되지 않았다. 15wt%와 20wt% BaCe$O_{3}$첨가한 시편에서는 자장이 증가하면 자화율차이가 단순히 감소한다. Y-Ba-Cu-O의 flux pinning 기구를 BaCe$O_{3}$첨가에 의한 미세조직변화로 설명하였다.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.51-55
• /
• 2000

Using modified melt-textured grown targets, YBa$_2$Cu$_3$O$_{7-{\delta}}$ thin films were prepared by pulsed laser deposition technique at the laser energy density from 1 J/cm$_2$ to 4 J/cm$_2$. All the films showed c-axis preferred orientations, however, a-axis outgrowths on the film surface were considerably increased with an increase of the laser energy density. To examine the origin of the a-axis outgrowth formation, the microstructures of films deposited at 2 J/cm$_2$ and 4 J/cm$_2$ were investigated using X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy. It was shown that a significant number of Y$_2$O$_3$ inclusions were formed during the growth of c-axis oriented films at 4 J/cm$_2$. These inclusions formed nucleation sites for the a-axis outgrowths. It is considered that, due to the unstable growth conditions with a high flux density of incident vapor species and the strain induced by the surrounding c-axis films, the Y$_2$O$_3$ inclusions would prefer the nucleation of α-axis grains.

• Korean Journal of Materials Research
• /
• v.8 no.2
• /
• pp.105-113
• /
• 1998

용융집합조직 YBaCuO 초전도체의 부상력에 미치는 변수들에 대하여 연구하였다. 초전도체의 부상력은 초전도체를 냉각하는 방법, 초전도결정의 방위, 시편의 두께 및 영구자석의 극성변화에 따라 달라짐을 알 수 있었다. 무자력 냉각한 초전도체에서는 큰 부상력과 작은 일력성분의 얻어지는 반면, 자력냉각한 시료에서는 반대의 결과가 얻어졌다. 이는 초전도체내에 포획된 자력양이 서로 다르고, 이들의 외부자장에 대한 상호작용이 다르기 때문인 것으로 판단된다. 초전도체의 부상력은 외부자력의 방향이 초전도결정의 c축과 평행할 경우 (H//c-axis)가 c-축과 수직한 경우(H//ab-axis)보다 부상력이 2-3배 컸다. 표면자력 3500gauss의 영구자석을 사용할 경우 초전도체의 두께가 8mm이상에서 초전도체의 부상력은 거의 일정하나 그 이하의 두께에서는 두께감소에 따라 선형적으로 감소하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.2
• /
• pp.110-113
• /
• 2016

(YNdSm)-Ba-Cu-O system high Tc composite superconductors were directionally grown by zone melting process, having large temperature gradient, in air atmosphere. Cylindrical green rods of $(YNdSm)_{1.8}Ba_{2.4}Cu_{3.4}O_x$ [(YNS)1.8]composite oxides by CIP (cold isostatic pressing) method using rubber mold were fabricated. The microstructure and superconducting properties were investigated by XRD, TEM and SQUID magnetometer. The size of nonsuperconducting $(YNdSm)_2BaCuO_5$ inclusions of the melt-textured (YNS)1.8 sample with $CeO_2$ additive were remarkably reduced and uniformly distributed within the superconducting (YNS)1.8 matrix. (YNS)1.8 samples, with / without $CeO_2$ additive, showed an onset $T_c{\geq}90K$ and sharp superconducting transition. The critical current density $J_c$ value of the (YNdSm)1.8 superconductor with $CeO_2$ additive were 840 A, $1.2{\times}104A/cm^2$ in 77 K, 0 Tesla by direct current transport method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.05a
• /
• pp.80-83
• /
• 2003

$SrSO_4$ were systematically added on Bi2212 from 0 to 10wt% to study the effect of Bi2212 superconductor tube characteristics. After mixing, the melted solution of Bi2212 and $SrSO_4$ was initially poured into the cylinder type of steel mold preheated at $550^{\circ}C$ for 30min and rotated at 1000rpm. Following that, tube was annealed at $840^{\circ}C$ for 72hrs. The tube dimension was 60 in diameter, 60mm in length and 2mm in thickness. XRD data suggests that there was no typical segregation phase related with $SrSO_4$. Well textured grain with typical 2212 phase was observed and average size was $20{\mu}m$. The measured critical current and critical current density of Bi2212 tube added by 5% $SrSO_4$ at 77K were 495A and $202A/cm^2$ respectively.

• Journal of the Korean Magnetics Society
• /
• v.2 no.3
• /
• pp.233-238
• /
• 1992

Melt-spun $Nd_{14}Fe_{76}Co_4B_6$ and $Nd_{10.5}Fe_{79}Co_2Zr_{1.5}B_7$ ribbons were prepared under an externally applied magnetic field. Magnetic properties in terms of anisotropy were evaluated by discussing the effect of textured structure of the ribbon samples as well as its powders. About 32 % increase in $(B{\cdot}H)_{max}$ and 18.8 % increase in $B_r$ were observed along the perpendicular direction of the ribbon plane which is more prominent for the Nd-Fe-Co-Zr-B than for the Nd-Fe-Co-B alloy. The enhancement of magnetic anisotropy was monitored by measuring the anisotropy constant of each alloy as a function of quenching rate of the ribbon. It was found that for the melt-spun ribbon quenched at slow rate(less than 7 m/s) the magnetic field effect was overwhelmed by the heat gradient effect through the ribbon thickness while the field effect was prominent at intermediate quenching rate (more than 7~11 m/s). The reproducible maximum energy product, $(B{\cdot}H)_{max}$=16.4 MGOe can be obtained from the Nd-Fe-Co-Zr-B alloy.

• Korean Journal of Materials Research
• /
• v.5 no.7
• /
• pp.880-887
• /
• 1995

Melt spun YB $a_2$C $u_3$A $g_{15}$ and YbB $a_2$C $u_3$A $g_{x}$(x=5, 16 and 53) precursor alloy ribbons were oxidized at 263~322$^{\circ}C$, and heat-treated at 872~89$0^{\circ}C$ under 1.0atm oxygen pressure. In addition, about ten ribbons were stacked and coupled by pressing, and then followed the same heat treatment. YB $a_2$C $u_3$ $O_{7-{\delta}}$(1-2-3) or YbB $a_2$C $u_3$ $O_{7-{\delta}}$(1-2-3) phase was formed in both the ribbons and the multilayered specimens. The formed 1-2-3 phases were not texturized in all the ribbons, but slightly texturized in the multilayered specimens. $J_{c}$ was not achieved in all the ribbons at 77K and zero magnetic field. Among the multilayered specimens, YB $a_2$C $u_3$A $g_{15}$ and YbB $a_2$C $u_3$A $g_{16}$ showed $J_{c}$ of 260 and 180A/$\textrm{cm}^2$, respectively. YB $a_2$C $u_3$A $g_{15}$ and YbB $a_2$C $u_3$A $g_{16}$ are considered to be the appropriate compositions in producing textured superconducting oxides with improved $J_{c}$ by pressing. Onset critical temperature ( $T_{on}$ ) of the multilayered YB $a_2$C $u_3$A $g_{15}$ was 92K while those of YbB $a_2$C $u_3$A $g_{x}$(x=5 , 16 and 53) were 88~90K. , 16 and 53) were 88~90K.

• The Journal of the Petrological Society of Korea
• /
• v.19 no.3
• /
• pp.227-244
• /
• 2010

Abundant spinel lherzolite xenoliths showing distinctively different textural types such as protogranular, porphyroclastic, and mylonitic texture are trapped in the basaltic rocks from southeastern part of Jeju Island. These xenoliths show the textural spectrum from coarse-grained protogranular through porphyroclastic with bimodal grain size to fine-grained and foliated mylonitic texture. They tend to decrease in grain sizes and show more linear grain boundaries and more frequent triple junctions from protogranular through porphyroclastic to mylonitic. Spinel has different occurrence mode according the textural type. Spinel is always associated with orthopyroxene in protogranular texture, whereas it is scattered and independent of orthopyroxene in mylonitic texture. Additionally, porphyroblast from porphyroclastic and mylonitic textures has internal deformation features such as kink band, undulatory extinction and curved lamella, whereas neoblast is strain-free. These textural features indicate increasing degree of static/dynamic recrystallization from protogranular through porphyroclastic to mylonitic texture. The mg#[$=100{\times}Mg/(Mg+Fe_t)$] of olivine, orthopyroxene and clinopyroxene is relatively constant (ol: 88-91; opx: 89-92; cpx: 89-92) regardless of textural differences. The mg# of constituent minerals, NiO content (0.3~0.4 wt%) and MnO content (0.1~0.2 wt%) of olivine are similar to those of mantle xenoliths worldwide, also indicating that studied spinel lherzolite xenoliths were mantle residues having experienced 20~25% partial melting. The geochemical and textural characteristics have close relations showing that LREE and incompatible trace elements content of orthopyroxene and clinopyroxene increases from protogranular through porphyroclastic to mylonitic. These observations suggest that the studied mantle xenoliths experienced metasomatism by LREE enriched melt or fluid after partial melting, indicating a close relation between deformation and metasomatism. The metasomatism was possibly confined to narrow shear zones from where porphyroclastic and mylonitic textured xenoliths originated. These shear zones might favorably drive the percolation of LREE-enriched melts/fluids responsible for the metasomatism in the lithospheric mantle below the Jeju Island.