Earticle

MgB2 bulk samples are synthesized through solid state reaction route using Mg precursors with different particle size by keeping the boron precursor unchanged. Scanning electron microscopy study of the fractured surface for all the samples depicts quite distinct structure depending on the Mg precursor. Big size of Mg precursor resulted in to largely elongated and deep pores while smaller one gave roughly ellipsoidal and shallow pore structure. Influence of the Mg particle size on the grain to grain connectivity reflected in the critical current density value which was greater for samples with smaller Mg precursor. All the synthesized samples undergo a superconducting transition at around 36.5 K irrespective of different Mg precursor particle size.

과학과 종교의 상충되는 논점은 현상이론의 충돌과 그 충돌로부터 이론을 조화 시켜가는 갈등해소과정으로 사료된다. 그러나 과학과 종교의 조화로운 진보 과정 을 논술할 수 있는 기능이 가능해진 현재의 과학과 종교의 관계에도 근본주의에 입각해 창조주의 논리만을 유지하는 과정 또한 존재한다. 반면에 통일사상과 같이 명백한 양자론적인 과학적 사실들을 하나의 새로운 기조로 받아들이거나, 이런 과 학적 사실들을 통일신학 및 사상에 접목하여 인류에 봉헌하는 가르침으로 신학적 진실을 탐구하려는 움직임도 노도의 물결과 같이 거세지고 있다. 과학적 진리는 인간의 경험에 입각한 직관적인 사실에 유래한다는 것이 경험주의의 입장이다. 경 험주의의 기본원리는 과학적 개념과 의미가 실제적인 경험과 연결되었을 때만 증 명될 수 있으며, 과학적 명제나 신념의 타당성은 반드시 과학적 사실에 의존하고 있다는 것이다. 본 연구에서 시도하고자 하는 초전도 공학과 통일사상과의 효율적 인 접목을 시도하는 작업은 현재까지 과학 및 종교적인 관점에서 시도된 적이 없 는 연구 수행으로 판단된다. 본 연구자의 통일사상에 관한 이해도는 매우 미천한 실정이다. 다만, 본 연구자의 분석에 의하면 통일사상이 매우 과학적이고 통일사상 설립자의 과학에 근거한 말씀이 현대 과학을 정립한 알버트 아인슈타인(Albert Einstein)의 양자학 논점과도 일맥상통하고 있는 과학적 논점 등이 발견되고 있다. 따라서 본 연구와 같이 객관적인 과학적 연구 결과를 통일사상이라는 논리적인 관 점에서 바라보는 시도를 통해 매우 의미있는 연구수행 과정이 그려질 것이다.

Resolving the conflict between science and religion needs to harmonize theories from the clash phenomena. However, the current relationship between science and religion, which has become possible to describe a harmonious progress of science and religion, also involves a process of maintaining the fundamentalist logic. On the other hand, the movement to explore theological truth needs to accept clear quantum scientific facts such as the idea of unification as a new basis and combine scientific facts with the idea of Unification Theology to serve humanity. The position of empiricism is that scientific truth comes from intuitive facts based on human experience. The basic principle of empiricism can only be proved when scientific concepts and meanings are linked to practical experiences. The validity of scientific propositions or beliefs is necessarily dependent on scientific facts. However, it is judged that the work of attempting to efficiently connect superconducting engineering with the idea of ‘unification’ in Unification Thought(UT) which is attempted in this study is a research that has never been attempted from a scientific and religious point of view. This researcher's understanding of the idea of ‘unification’ in UT is very humble. However, according to this researcher's analysis, the following scientific points are found: 1)1) the idea of ‘unification’ is very scientific; and 2) 2)words based on the science given by the founder in the idea of unification are consistent with Albert Einstein's quantum theory which has established modern science. Thus, attempts to look at objective scientific research results from the logical point of view of the idea of unification such as this study will draw a very meaningful process of conducting research.

We studied the distribution of the current density and its magnetic-field dependence in GdBCO coated conductors with AC bias currents using low temperature scanning Hall probe microscopy. We selectively measured magnetic field profiles from AC signal obtained by Lock-in technique and calculated current distributions by inversion calculation. In order to confirm the AC measurement results, we applied DC current corresponding to RMS value of AC current and compared distribution of AC and DC transport current. We carried out the same measurements at various external DC magnetic fields, and investigated field dependence of AC current distribution. We notice that the AC current distribution unaffected by external magnetic fields and preserved their own path on the contrary to DC current.

In this study, a SFCL-combined DC circuit breaker system was proposed by applying the current-limiting technology for DC circuit breaking. The SFCL-combined circuit breaker system consists of a mechanical DC circuit breaker combined with superconductors. To ensure the reliable structure and operation of the SFCL-combined circuit breaker system, a simulation grid was designed using the EMTDC/PSCAD program, and simulation was conducted. The results showed that the SFCL-combined DC circuit breaker system with superconductors limited the maximum fault current by 37%. In addition, the burden on the DC circuit breaker was decreased by 87%.

Superconducting properties of thin film MgB2 superconductors irradiated with 45 MeV α-particle beam were studied. After the irradiation, enhancement of the critical current density and pinning force was observed, scaling close to strong pinning formula. Double logarithmic plots of the maximum pinning force density with irreversible magnetic field show a power law behavior close to carbon-doped MgB2 film or polycrystals. Variation of normalized pinning force density in the reduced magnetic field suggests scaling formulas for strong pinning mechanism like planar defects. We also observed a rapid decay of critical current density as the vortex lattice constant decreases, due to the strong interaction between vortices and increasing magnetic field.

We fabricated MHOS (multi-HTS layers on one substrate) high-temperature superconducting (HTS) REBCO conductors using HTS REBCO coated conductor (CC) A-specimen, which induces an artificial magnetic flux pinning effect, and HTS REBCO CC B-specimen, that does not induce this effect. The superconducting magnetic properties of the fabricated MHOS conductors were examined by measuring their magnetic moment m(H) curves using a physical property measurement system (QD PPMS-14). The critical current density (Jc) characteristics of our four-layered MHOS HTS REBCO conductor specimens such as BAAB, BBBB, and AAAA were lower than those of their two-layered and three-layered counterparts. At a temperature T of 30 K the magnetic flux pinning physical indicator δ values (obtained from the relationship Jc ∝ H-δ) of the three-layer ABA (δ = 0.35) and two-layer AB (δ = 0.43) specimens were found to be significantly lower than those of the four-layer ABBA (δ = 0.51), BAAB (δ = 0.60), AAAA (δ = 0.78) and BBBB (δ = 0.81) structures.

The superconducting properties of high temperature superconducting (HTS) GdBCO coated conductor (CC) tape (Ag/GdBCO/Buffer-layers/Stainless Steel) were investigated, specifically a series of samples prepared by vacuum heat treatment (200oC to 600oC), using a Quantum Design PPMS-14. The critical current density Jc value was obtained by applying the modified Bean model to the irreversible magnetization Mirr(H) data which was estimated from the magnetization M(H) loop. The reduction rates of lnJc and Tc values according to the increase of the vacuum annealing temperature Tan were d(lnJc)/dTan= - 0.016 A/(cm2∙oC) and dTc/dTan = - 0.24, respectively. We examined the effect of recovery temperature Tre (475oC to 700oC) and recovery duration time t (0.5 h to 24 h) on the restoration of previously completely lost superconductivity in samples that subsequently received heat treatment in an O2 gas flow space. All samples were fully restored to superconductivity by heat treatment in an O2 gas flow space. The recovery temperatures Tre (475oC to 700oC) and recovery duration times t (0.5 h to 24 h) were both independent of the superconductivity recovery characteristics.

The magnetic properties of heat treated O-series high temperature superconducting (HTS) GdBCO coated conductor (CC) tapes which were formed of Ag/GdBCO/Buffer-layers/Stainless Steel (SS), were investigated by employing a Quantum Design PPMS-14. Using a modified Bean model, the critical current density Jc values have been estimated from the mirr(H) data, which are obtained by measuring the magnetic moment m(H) loops. For a range of intermediate fields, which are interacting or collective flux pinning area, the magnetic flux behaviors were investigated from the relationship Jc  H-. In addition, the changes of irreversibility magnetic field Hirr line of heat-treated O-series HTS GdBCO CC tapes were analyzed, according as the annealing temperature under oxygen flowing increases. Both weak and strong break-downs were found by examining the changes of irreversibility magnetic field Hirr lines.

We have investigated the effect of Y2O3 nanoparticles on the pinning properties of Y2O3-doped GdBa2Cu3O7-δ (GdBCO) films. Both undoped and Y2O3-doped GdBCO films were grown on CeO2-buffered MgO (100) single crystal substrates by pulsed laser deposition (PLD) using KrF (λ=248 nm) laser. The Y2O3 doping contents were controlled up to ~ 2.5 area% by varying the internal angles of Y2O3 sectors put on the top surface of GdBCO target. Compared with the Gd2O3-doped GdBCO films previously reported by our group [1], the Y2O3-doped GdBCO films exhibited less severe critical temperature (Tc) drop and thus slightly enhanced critical current densities (Jc) and pinning force densities (Fp) at 65 K for the applied field parallel to the c-axis of the GdBCO matrix (B//c) with increasing the doping content. Below 40 K, the in-field Jc and Fp values of all Y2O3-doped GdBCO films exhibited higher than those of undoped GdBCO film, suggesting that Y2O3 inclusions might act as effective pinning centers.

We investigate the upper critical field anisotropy ΓH and the magnetic penetration depth anisotropy Γλ of a high-quality FeSe1-x single crystal using angular dependent resistivity and torque magnetometry up to 14 T. High quality single crystals of FeSe1-x were successfully grown using KCl-AlCl3 flux method, which shows a sharp superconducting transition at TC ~ 9 K and a high residual resistivity ratio of ~ 25. We found that the anisotropy ΓH near TC is a factor of two larger than found in the poor-quality crystals, indicating anisotropic 3D superconductivity of FeSe1-x. Similar to the 1111-type Fe pnictides, the anisotropies Γλ and ΓH show distinct temperature dependence; ΓH decreases but Γλ increases with lowering temperature. These behaviors can be attributed to multi-band superconductivity, but different from the case of MgB2. Our findings suggest that the opposite temperature dependence of Γλ and ΓH is the common properties of Fe-based superconductors.

Among elemental metals, niobium (Nb) has the highest superconducting transition temperature (Tc) at ambient pressure. Thus, Nb films have been used in superconducting electronics and radio frequency cavity applications. In this study, the depositional factors determining the crystallinity and Tc of Nb films were investigated. An Nb film grown at a sputtering temperature of 240°C exhibited the maximum crystallinity of Nb and the minimum crystallinity of niobium oxide. X-ray photoelectron spectroscopy confirmed a maximum atomic percent of niobium and a minimum atomic percent of oxygen. A sputtering power of 210 W and a sputtering time of 50 min were the optimal conditions for Nb deposition, and the Tc of the optimized film (9.08 K) was close to that of bulk Nb (9.25 K). Transmission electron microscopy images of the thick film directly confirmed the removal of the typical in-plane compressive strain in the (110) plane caused by residual stress.

Hydrogen, the lightest and the most abundant element in the universe becomes a mainstay of contemporary condensed matter physics, which is largely because its metallization is regarded as the holy grail of high-pressure physics and it is also due to recent observations of high Tc superconductivity in hydrogen-dense compounds at extremely high pressure. Contemporary static high-pressure technique is not enough to realize the metallization of solid hydrogen and hydrogen-dense compounds may significantly reduce the required transition pressure providing an excellent proxy study. In this brief review, I will introduce recent achievements of high-pressure study in solid hydrogen and hydrides.

Suppression of the superconducting transition temperature (Tc) of NbN thin films in superconductor/ferromagnet multilayers has been investigated. Both superconducting NbN and ferromagnetic FeN layers were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an Ar-N2 gas mixture. The thickness of FeN films was fixed at 20 nm, while the thickness of NbN films was varied from 3 nm to 90 nm. Tc suppression was clearly observed in NbN layers up to 70 nm thickness when NbN layer was in proximity with FeN layer. For a given thickness of NbN layer, the magnitude of Tc suppression was increased in the order of Si/FeN/NbN, Si/NbN/FeN, and Si/FeN/NbN/FeN structure. This result can be used to design a spin switch whose operation is based on the proximity effect between superconducting and ferromagnetic layers.