| 학회 | 한국재료학회 |
| 학술대회 | 2018년 가을 (11/07 ~ 11/09, 여수 디오션리조트) |
| 권호 | 24권 2호 |
| 발표분야 | H. 한-일 재료공학(KJMST 2018) |
| 제목 | Magnetic and structural properties of superconducting mixed anion layered compound, La(Ca)FeAsO(F) |
| 초록 | Mixed Anion Layered Compounds (MALC) have various electrical and functional properties such as p-type semiconducting properties, high thermoelectric performance and high superconducting transition temperature (Tc) superconductivity. Since the discovery of high Tc superconductivity in Iron-based MALC, LaFeAsO1-xFx by Y.Kamihara et al, MALC have been expected as mother compounds for such Iron-Based Superconductors. This discovery had the strong impact because of having broken the widely accepted belief that iron is antagonistic against the high Tc superconductivity. The Tc in bulk Iron-Based Superconductors is raised up to 58.1 K at SmFeAsO1-xFx under ambient pressure by M.Fujioka et al. LaFeAsO has a layered crystal structure belonging to the tetragonal P4/nmm space group. At low temperature, structural transition occurs from tetragonal to orthorhombic and anti-ferromagnetic phase appears. Superconductivity emerges when this transition is suppressed by electron doping via F substitution. The maximum Tc of LaFeAsO1-xFx is 26 K at x = 0.11. In our research polycrystalline samples of La and Ca co-doped LaFeAsO, La1-xCaxFeAsO1-yFy were synthesized. And their electrical, structural and magnetic properties were examined to investigate the possibility to rise the Tc by electron and hole co-doping. Polycrystalline La1-xCaxFeAsO1-yFy [nominal (x, y) = (0.50, 0.50), (0.25, 0.25), (0.25, 0.30), (0.25, 0.40) and (0.25, 0.50)] samples were synthesized by solid-state reaction. Grinding and weighing procedures were done in Ar atmosphere. LaAs, FeAs and Fe2As were prepared by heating stoichiometric mixtures of La, Fe and As in evacuated silica tubes. Then, La1-xCaxFeAsO1-yFy samples were synthesized by heating stoichiometric mixtures of LaAs, FeAs, Fe2As, CaF2, dehydrated La2O3 and dehydrated CaO powders in evacuated silica tubes at 1000 °C for 40 h. The crystallographic phases of samples were examined by powder X-ray diffraction (XRD) (Rigaku RINT2500 Ultra18) using Cu Kα radiation. And lattice constants of these samples were calculated by least squares method. And the structures were refined by Rietveld Analysis using RIETAN-FP-Venus program. The electrical resistivity of the samples was measured by DC four probe technique. The magnetization measurements were performed on a superconducting quantum interference device (SQUID) magnetometer (Quantum Design magnetic property measurement system (MPMS)) at 4.2 K and 20 K from -6.0 kOe to 6.0 kOe. For the samples at nominal (x, y) = (0.50, 0.50), (0.25, 0.25) and (0.25, 0.30), an anomalous kink (Tanom) which corresponds to a structural transition was observed around 140 ~ 150 K. For the samples at nominal (x, y) = (0.25, 0.40) and (0.25, 0.50), the normal-state resistivity decreased and superconducting transitions were observed. Tc was observed at 25.7 K and 31.5 K for nominal (x, y) = (0.25, 0.40) and (0.25, 0.50). Tc of the nominal (x, y) = (0.25, 0.50) sample is higher than that of LaFeAsO1-xFx. The magnetization measurements revealed that these two samples exhibit diamagnetism induced by the superconductivity at 4.2 K and 20 K. The superconducting volume fractions (SVF) of the samples at nominal (x, y) = (0.25, 0.40) and (0.25, 0.50) were ~ 44.5% and ~28.0% at 4.2 K respectively. This indicates that both samples have bulk superconductivity. |
| 저자 | Kodai KANEYASU1, Masanori MATOBA2, Yoichi KAMIHARA3 |
| 소속 | 1Department of Applied Physics and Phisico-Informatics, 2Faculty of Science and Technology, 3Keio Univ. |
| 키워드 | Mixed Anion Layered Compound; Iron-Based Superconductor; SQUID; Solid state reaction |
