• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.221-223
• /
• 1999

In this work, samples were manufactured variously by changing conventional calcining and sintering conditions and we tried the utilization by making the heat treatment time, which is demanded to high-Tc phase formation, much shorter. We found out optimal heat treatment conditions with the analysis on formation process at superconducting phase in term of the change of calcining and sintering time and then, examined X-ray diffraction(XRD) patterns, scanning electron microscope(SEM) measurement and energy dispersive X-ray spectrometer(EDX) of the samples manufactured under heat treatment conditions which we suggest here. As a result, 2223 high-$T_c$, phase of (Bi,Pb)SrCaCuO superconductor starting with ($Bi_l$ xPbx,)$_2$$Sr_2$$Ca_2$$Cu_3$$O_y$, composition was formed from 1 hr sintering sample at temperature nearby melting point and also the completed sample with calcining and sintering time of 9 hr was formed high-$T_c$.low-$T_c$ phase appearing in sight above the critical temperature of liquid $N_2$.

• 한국초전도학회:학술대회논문집
• /
• v.14
• /
• pp.30-30
• /
• 2004

• Korean Journal of Microbiology
• /
• v.36 no.2
• /
• pp.91-96
• /
• 2000

The cultural and physiological conditions for the T-2 toxin [4,15-diacetoxy-8-(3-mety1butyloxy)-12,13- epoxy-trichothec-9-en-3-01, $C_{24}H_{30}O_9$] production by Fusarium spp. were studied. Thin layer chromatography (TLC) assay and the microbiological assay uslng Rhodotomla rubra were used to quantitate tbe T- 2 toxin. Among the four strains of Fusarium spp., F tn'cinctum NRRL 3299 was best for T-2 toxin production. In solid culture, white com grit medium was best for T-2 toxm production. Temperature played a critical role in the production of T-2 toxin. T-2 toxin production was favored by long duration of low-temperature incubation. The growth and toxin production were relatively high on galactose, fructose, glucose, and sucrose media, when each was used as a sole carbon source, and relatively low on sorbitol, glycerol, and lactose media. For nitrogen sources, $NH_4^(+) and NO_3^{-}were used well as a sole nitrogen source, but $NO_2^-$ was not used. Initial pH and speed of shaker also affected the production of T-2 toxin. From temperature shifting experiment, it is clear that T-2 toxin metabolic pathway is regulated by temperature-dependent enzyme depression or enzyme induction system.

• Korean Journal of Materials Research
• /
• v.21 no.2
• /
• pp.73-77
• /
• 2011

Specific heat of a crystal is the sum of electronic specific heat, which is the specific heat of conduction electrons, and lattice specific heat, which is the specific heat of the lattice. Since properties such as crystal structure and Debye temperature do not change even in the superconducting state, the lattice specific heat may remain unchanged between the normal and the superconducting state. The difference of specific heat between the normal and superconducting state may be caused only by the electronic specific heat difference between the normal and superconducting states. Critical temperature, at which transition occurs, becomes lower than $T_{c0}$ under the influence of a magnetic field. It is well known that specific heat also changes abruptly at this critical temperature, but magnetic field dependence of jump of specific heat has not yet been developed theoretically. In this paper, specific heat jump of superconducting crystals at low temperature is derived as an explicit function of applied magnetic field H by using the thermodynamic relations of A. C. Rose-Innes and E. H. Rhoderick. The derived specific heat jump is compared with experimental data for superconducting crystals of $MgCNi_3$, $LiTi_2O_4$ and $Nd_{0.5}Ca_{0.5}MnO_3$. Our specific heat jump function well explains the jump up or down phenomena of superconducting crystals.

• Progress in Superconductivity
• /
• v.10 no.2
• /
• pp.74-78
• /
• 2009

Inter-grain nanobridges of the $MgB_2$ superconductor have been fabricated by focused-ion-beam(FIB) and their electrical transport properties were studied. The $MgB_2$ film was prepatterned into microbridges by a standard argon ion milling technique and then FIB-patterned into 100 nm$\times$100 nm bridges. Current-voltage characteristics showed a strong flux-flow type behavior at all temperatures with a trait of Josephson coupling near $T_c$. At low temperatures, the curves showed a two-step resistance-doubled transition with occasional hysteresis. The resistance-doubling transition is believed to be due to a two-channel flux-flow effect. The temperature-dependent critical current data showed $I_c(T){\propto}(1-T/T_c)^2$ near $T_c$, same as a normal barrier junction, and $I_c(T){\propto}(1-T/T_c)^{1.2}$ at low temperatures, similar to that of a film.

• Electrical & Electronic Materials
• /
• v.7 no.4
• /
• pp.289-293
• /
• 1994

Thin films of YB $a_{2}$C $u_{3}$$O_{7-x}$ supercondYB $a_{2}$C $u_{3}$$O_{7-x}$uctor were prepared on (100) SrTi $O_{3}$ substrates by pulsed laser deposition using visible light laser. Q-switched Nd:YAG(532 nm, 30 ns) pulsed laser was used for deposition. The effects of substrate temperature and oxygen pressure during deposition on films were studied. Critical current density of 2.93*10$^{6}$ A/c $m^{2}$ at 77K and Tc(zero)=91.7K were obtained from the film prepared with Tsub=745.deg. C and $P_{02}$=200 mTorr. XRD analysis showed that the grown film has c-axis normal orientation to the substrate surface and has single phase. Surface morphology of the film has been improved by interfering the plume ejected from YB $a_{2}$C $u_{3}$$O_{7-x}$ target.arget.t.

• Progress in Superconductivity and Cryogenics
• /
• v.17 no.3
• /
• pp.1-4
• /
• 2015

Production of $MgB_2$ film on metallic Hastelloy with SiC as the buffer layer was achieved by means of hybrid physical-chemical vapor deposition technique, whereas SiC buffer layers with varied thickness of 170 and 250 nm were fabricated inside a pulsed laser deposition chamber. Superconducting transition temperature and critical current density were verified by transport and magnetic measurement, respectively. With SiC buffer layer, the reduced delaminated area at the interface of $MgB_2$-Hastelloy and the slightly increased $T_c$ of $MgB_2$ tapes were clearly noticed. It was found that the upper critical field, the irreversibility field and the critical current density were reduced when $MgB_2$ tapes were buffered with SiC buffer layer. Clarifying the mechanism of SiC buffer layer in $MgB_2$ tape in affecting the superconducting properties is considerably important for practical applications.

• Progress in Superconductivity and Cryogenics
• /
• v.6 no.4
• /
• pp.9-12
• /
• 2004

We report a successful fabrication of high-$J_C$ $NdBa_2Cu_3O_{7-{\delta}}$ (NdBCO) films on (100) $SrTiO_3$ substrates by pulsed laser deposition (PLD) in high oxygen pressures ranging from 400 to 800 mTorr. Fabricated NdBCO films exhibited only c-axis orientation, good out-of-plane and in-plane textures, and also excellent superconducting properties, including critical temperature ($T_C$) and critical current density ($J_C$) of above 90 K and the highest of $3.1MA/cm^2$ at 77 K in self-field, implying that NdBCO is a perspective alternative to YBCO for coated conductor. In low oxygen pressures ranging from 100 to 200 mTorr, however, the films showed a-, c-mixed orientation and degraded $T_{C,zero}$ values due to the formation of $Nd_{1+x}Ba_{2-x}Cu_3O_{7-{\delta}}$-type solid solutions with an excessive substitution of $Nd^{3+}$ ions for the $Ba^{2+}$ sites.

• Journal of Magnetics
• /
• v.16 no.1
• /
• pp.15-18
• /
• 2011

We have studied the $TiO_2$ doping effects on the flux pinning behavior of an $MgB_2$ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of $TiO_2$-doped $MgB_2$ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped $MgB_2$. The critical current density was estimated from the width of hysteresis loops in the framework of Bean's model at different temperatures. The obtained results manifest that nano-scale $TiO_2$ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a $TiO_2$-doped $MgB_2$ superconductor.

• 한국신재생에너지학회:학술대회논문집
• /
• 2008.10a
• /
• pp.254-257
• /
• 2008

For crystalline slags, of which the viscosity rapidly increases at $T_{cv}$ due to the formation of crystalline phases, the Tcv is affected by measurement conditions. In this study, we investigated the effect of cooling rate, and alumina dissolution on the determination of $T_{cv}$. Using synthetic slag samples based on the composition of Alaska Usibelli slag, $T_{cv}$ were determined under a constant cooling rate of $2^{\circ}C$/min, and under rapid cooling with holding time to allow the slag to reach thermal and rheological equilibrium. The effect of alumina dissolution was investigated using platinum lined crucibles. The constant cooling resulted in lower $T_{cv}$ by $33^{\circ}C$ as compared to the equilibrium measurements. Under $2^{\circ}C$/min cooling, the blocking alumina dissolution resulted in lower $T_{cv}$ by $23^{\circ}C$. When the $T_{cv}$ was measured under $2^{\circ}C$/min cooling using an alumina crucible, therefore, the effects of a constant cooling is somewhat offset by the alumina dissolution effect, and bring the measured value closer to the true value.