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Single-crystal growth of rutheno-cuprate materials EuSr2RuCu2O8−δ (RuEu-1212) and (Eu, Ce)2Sr2RuCu2O10−δ (RuEu-1222), where RE denotes a rare-earth element, remains a major challenge, especially for Eu-substituted RuEu-1212 and RuEu-1222 systems, which require removing the magnetic effect of Gd to investigate coexistence of superconductivity on CuO2 and magnetism of Ru. In this study, RuEu-1212 and RuEu-1222 single crystals are prepared via the partial melting technique. The maximum size of grown single crystals of RuEu-1212 was 80 $$\mu$$ m, which is five times larger than in previous studies. Although superconductivity disappeared in the large crystals, a magnetic transition due to Ru was observed at 130–140 K. Meanwhile, platelike RuEu-1222 single crystals with a length of 30 $$\mu$$ m were successfully prepared. After optimizing the sintering conditions, the onset temperature of superconducting transition (Tc-onset) reached close to 40 K and diamagnetism was observed below 20 K, which is almost consistent with the offset temperature of the superconducting transition (Tc-offset) value from the resistance–temperature (R–T) characteristics. The initial magnetization curve at 5 K shows diamagnetism clearly. The Tc-onset and Tc-offset values were 44.3 K and 22.5 K, respectively, which are the highest values of any rutheno-cuprates synthesized by partial melting to date.

RhPb2 (rhodium dilead) is a superconductor crystallizing in the CuAl2 structure type (space group I4/mcm). The Rh and Pb atoms are located at the 4a (site symmetry 422) and 8h (m.2m) sites, respectively. The crystal structure is composed of [RhPb8] antiprisms, which share their square faces along the c axis and the edges in the direction perpendicular to the c axis. We have succeeded in growing single crystals of RhPb2 and have re-determined the crystal structure on basis of single-crystal X-ray diffraction data. In comparison with the previous structure studies using powder X-ray diffraction data [Wallbaum (1943). Z. Metallkd. 35, 218–221; Havinga et al. (1972). J. Less-Common Met. 27, 169–186], the current structure analysis of RhPb2 leads to more precise unit-cell parameters and fractional coordinates, together with anisotropic displacement parameters for the two atoms. In addition and likewise different from the previous studies, we have found a slight deficiency of Rh in RhPb2, leading to a refined formula of Rh0.950 (9)Pb2.

Single crystals of the rutheno-cuprate magnetosuperconductor (RE, Ce)2Sr2RuCu2O10−δ (RE = Gd, Eu) were successfully synthesized using the self-flux method. The size of one side of the single crystals reached 100 µm for Gd and 20 µm for Eu. This is the first report of the growth of single crystals of RuRE-1222 suitable for precise X-ray structural refinement. The crystal structures were determined for (Gd, Ce)2Sr2RuCu2O10−δ specimens synthesized from starting materials with two different Ru:Cu ratios. The two crystals exhibited a similar layered structure, although the lattice parameters a and c were smaller than those reported previously for polycrystalline samples. Strong thermal vibration of oxygen on the RuO2 plane was confirmed, and no canting of the Ru octahedra was observed. The calculated density of states based on this structural analysis indicated that superconducting layers composed of the CuO2 plane and fluorite-type Gd2O2 block intersect the Fermi level and that ferromagnetic layers composed of RuO2 octahedra are located in the vicinity of the Fermi level.

The crystal structure of type I clathrate Ba8Al16Ge30 prepared by arc melting in argon atmosphere has been studied by using a neutron powder diffractometer from 10 to 900 K. We found that the site preferences in the host structure were relevant to the guest atom features, which agrees with a previous report. Data were analyzed using two models for the Ba atom position in the larger cage (Ba2): an on-center 6d-site model and an off-center 24k-site one. The Maximum Entropy Method (MEM) results agree well with the 24k model and the shape of the nuclear density distribution of Ba2 atom evolves with increasing temperature.

Low-cost room-temperature sodium-ion batteries (SIBs) are expected to promote the development of stationary energy storage applications. However, due to the large size of Na+, most Na+ host structures resembling their Li+ counterparts show sluggish ion mobility and destructive volume changes during Na ion (de)intercalation, resulting in unsatisfactory rate and cycling performances. Herein, we report a new type of sodium iron phosphate (Na0.71Fe1.07PO4), which exhibits an extremely small volume change (~ 1%) during desodiation. When applied as a cathode material for SIBs, this new phosphate delivers a capacity of 78 mA·h·g−1 even at a high rate of 50 C and maintains its capacity over 5,000 cycles at 20 C. In situ synchrotron characterization disclosed a highly reversible solid-solution mechanism during charging/discharging. The findings are believed to contribute to the development of high-performance batteries based on Earth-abundant elements.

In this study, cubic single crystals of the magnetic superconductor Ru1−xSr2−yGd1+yCu2+xO8−δ (RuGd-1212) with typical dimensions of 100–150 µm in length were grown by the partial melting technique. Multiple 00l reflections were first observed by XRD measurements of the bulk RuGd-1212 single crystals. The resistivity of the obtained crystals was roughly estimated to be ∼24–80 mΩ cm and no superconducting transition was observed down to 4.2 K. From the XRD measurements and refinement of the crystal structure, it was apparent that the Ru and Sr sites of the single-crystal RuGd-1212 were partially substituted by Cu and Gd, respectively. Oxygen defects were found to be minor (δ ≈ 0.1). The lattice parameters a and c of the single crystals were found to be larger and smaller, respectively, than those of a polycrystalline sample.

The eutectic point for a typical gallium indium tin (GaInSn) alloy with an atomic composition of 78% Ga, 15% In, and 7% Sn is at near room temperature. This alloy exists in the liquid state at room temperature and solidifies below 260 K. We found that the major In3Sn and minor InSn4 superconducting phases are formed in this liquid alloy below 260 K and this alloy exhibits superconductivity at 6.0 K. Therefore, we can fabricate superconducting thick films without heat treatment by simply coating a substrate with the alloy and subsequently cooling it to the alloy's superconducting transition temperature.

To study the melting transition of a vortex crystal (or cluster) consisting of a small number of vortices confined in a mesoscopic-scale superconductor, $c$-axis magnetoresistance in the highly anisotropic high-${T}_{\mathrm{c}}$ superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+y}$ (Bi2212) has been measured using a triangle-shaped stack of intrinsic Josephson junctions, which was trimmed out from a single-crystal flake of Bi2212 via a double-sided etching process using a focused ion beam. We observed oscillations of the melting transition line, in which the oscillating part of the melting temperature has sharp peaks when the number of vortices $N$ exactly coincides with the triangular number $n(n+1)/2$ ($n$ is an integer number), at least for $Nl50$. This is in contrast to the case of square shapes where the enhancements appeared as broad peaks around $N={n}^{2}$. Furthermore, the field ranges of the $N$-vortex state expand at the triangular numbers of $N$, suggesting that the triangular number of vortices has a more stable configuration than the others. Numerical studies on the configuration of vortices in a triangle shape show that geometrical matching with no defect structures is realized at the triangular numbers, whereas an edge dislocation often appears in the other nonmatching cases. The degree of suppression of the melting temperatures at nonmatching numbers is reasonably consistent with the value estimated from the increase in free energy with the introduction of an edge dislocation.

We study the effects of the Al substitution by Ga on the crystal structures of type I clathrate Ba 8 Al 16-x Ga x Ge 30 (x = 2, 4, 6, and 8) by neutron powder diffraction. The diffraction data were refined using two models for Ba guest atom position in the oversized cage (Ba2): on center (6d site) and off-center (24k site) model. We also carried out the Maximum Entropy Method (MEM) analysis. The 24k model is in a good agreement with the Maximum Entropy Method (MEM) results. The evolution of nuclear density distribution with increasing temperature of Ba 8 Al 8 Ga 8 Ge 30 was revealed by MEM analysis.

Growth of single crystals of RuGd-1222 ((Gd,Ce)2Sr2RuCu2O10−δ) remains a major challenge, and previous studies have indicated that epitaxial thin films of these compounds exhibit deteriorated superconductivity. We have been working toward the synthesis of RuGd-1222 single crystals using the self-flux and partial melting techniques. In this paper, we report on the synthesis of RuGd-1222 single-crystal lumps by partial melting. The maximum size of a single crystal was approximately 80 μm in length, which is almost the same as that of our previous studies by self-flux method. Although these samples contained some impurity phases, the predominant phase was confirmed to be RuGd-1222. Furthermore, following optimization of the synthetic conditions, superconductivity with an onset transition temperature (Tc-onset) of 27 K was observed for a RuGd-1222 single-crystal lump prepared by partial melting. Local decomposition from RuGd-1222 plate-like crystals to RuGd-1212 single crystals was observed after prolonged sintering. The synthesis of single crystals of ruthenocuprates by partial melting is expected to contribute to an improved understanding of this class of magnetosuperconductors.

The fundamental and higher-harmonic susceptibilities χ n = χ n ′ − i χ n ′ ′ ( n = 1, 2, 3, 5 and 7) were measured to study the inter-grain superconducting properties of polycrystalline FeSr 2 YCu 2 O 6+ y . The real part χ 1 ′ and imaginary part χ 1 ″ appeared below T c1 = 56 K and T c2 = 45 K, respectively. T c1 and T c2 correspond to the onset temperatures of the superconductivity in individual grains and the superconductivity across grain boundaries, respectively. The higher-harmonic susceptibilities χ n ( n = 2, 3, 5 and 7) appeared below T c2 . The results suggest that the higher-harmonic susceptibilities were generated by the non-linear magnetization caused by the magnetic flux penetration through grain boundaries. The inter-grain magnetization curves were obtained by substituting measured χ n in Fourier series. The temperature dependence of χ n ( n = 1, 2, 3, 5 and 7) calculated by the Kim–Anderson critical-state model were approximately fitted with the observed those of χ n . The inter-grain critical-current density at 0 K under zero magnetic field was estimated at about 2 × 10 4 A/m 2 from the fitting parameters of the Kim–Anderson critical-state model. The magnetization curves and these parameters imply that the inter-grain critical-current density hardly depends on a weak magnetic field below 0.1 mT.

The occurrence of bulk superconductivity in the magnetosuperconductor GdSr2RuCu2O8−δ (RuGd-1212) remains controversial. Recently, we have successfully grown single crystals of RuGd-1212 with a size of 100 μm by partial melting. Although most single crystals prepared by conventional methods do not exhibit superconductivity, the superconductivity could be improved optimizing the synthetic conditions, and subtle changes in the sintering temperature were found to influence the emergence of superconductivity. Although most of the superconducting samples contained a small amount of the impurity phase Sr2GdRuO6, superconducting RuGd-1212 single crystals were the predominant phase. Furthermore, we successfully observed an onset transition temperature (Tc-onset) of 30 K and an in-plane critical current (Ic) of 12 mA. These experimental results indicate that the obtained RuGd-1212 single crystals exhibited bulk superconductivity.

By c -axis transport measurements in an intrinsic Josephson junctions (IJJs) stack of Bi 2 Sr 2 CaCu 2 O 8+y in magnetic fields parallel to c-axis, a penetration of individual vortices can be detected as a sudden jump or drop of c -axis resistance or critical current, which has already been reported in a sample of small in-plane area ( 2 ). We explored the individual vortex penetrations in IJJs stacks with much larger in-plane areas and successfully observed the same phenomenon even in a sample as large as 100 μm 2 . Behavior of the c -axis resistance and critical current caused by the individual vortex penetrations are investigated through the sample-size dependence in various temperatures and magnetic fields.

We report on the scanning tunneling microscopy (STM) and spectroscopy (STS) study on a newly discovered superconductor, Ir 1 − x Pt x Te 2 . We previously found that the sample which shows superconductivity forms so called “patchwork structure (PS)”. To obtain the spatial evolution of electronic structure on the PS, we performed STM/STS measurements on the PS. STS measurements revealed that an averaged spectrum shows the same energy asymmetry as that in the low temperature phase in the parent material, IrTe 2 . Furthermore, the spectrum at the trough on the PS is more asymmetric than that at the crest. This tendency is similar to that observed on the supermodulation in the low temperature phase in IrTe 2 .

An investigation was carried out into the distribution of Fe ions between Cu(1) and Cu(2) sites for FeSr 2 RECu 2 O 6 + y (RE = Eu, Er, Gd, Nd and Y), in addition to the structural, magnetic and electric properties. After a series of annealing steps to induce superconductivity, all samples exhibited a Ba 2 YCu 3 O 6 -type tetragonal crystal structure and the lattice constants increased with RE ion radius. Zero resistivity was observed for FeSr 2 YCu 2 O 6 + y , FeSr 2 ErCu 2 O 6 + y and FeSr 2 GdCu 2 O 6 + y . 57 Fe Mossbauer study revealed that for all samples except FeSr 2 NdCu 2 O 6 + y , about 10% of the Fe ions were present at Cu(2) sites. The separate three annealings are effective for FeSr 2 RECu 2 O 6 + y except FeSr 2 NdCu 2 O 6 + y for the suppression of Fe ion substitution at Cu(2) site and the carrier doping to CuO 2 plane.

It has recently been found that a large c -axis current injection into a stack of the intrinsic Josephson junctions (IJJs) of Bi 2 Sr 2 CaCu 2 O 8+y makes the doping level change reversibly and controllably [Y. Koval et al., Appl. Phys. Lett. 96 , (2010) 082507]. This can be one of promising in-situ methods to control superconducting properties, such as superconducting critical temperature T c of high- T c superconductors. We re-examined this doping process with changing the number of IJJs in a stack, and studied the influence on the vortex state, especially vortex lattice melting transition. Increase of the melting transition fields was observed by the current injection doping, suggesting the reduction of the anisotropy γ (=λ c /λ ab ). Dependence of the threshold voltage for the current injection doping on the number of IJJs, relaxation of the c -axis resistance in room-temperature undoping process, and the change of the anisotropy were evaluated.

The structure of Li{sub 2}MnO{sub 3}–LiCoO{sub 2} solid solutions or Li{sub 2−δ}(Mn{sub 1−x}Co{sub x}){sub 1+δ}O{sub 3} (LMCO) which are promising lithium-battery cathodes was studied by high-resolution electron microscopy (HREM). X-ray diffraction (XRD) analyses indicate that Li{sub 1.6}Mn{sub 0.2}Co{sub 1.2}O{sub 3} and Li{sub 1.7}Mn{sub 0.4}Co{sub 0.9}O{sub 3} take a rhombohedral (R3-bar m space group) structure, whereas Li{sub 1.85}Mn{sub 0.7}Co{sub 0.45}O{sub 3} and Li{sub 1.95}Mn{sub 0.9}Co{sub 0.15}O{sub 3} take a monoclinic (C2/m) superstructure. HREM studies on those samples reveal that all of the observed crystallites in sample Li{sub 1.95}Mn{sub 0.9}Co{sub 0.15}O{sub 3} contain sharp stripe structures due to the planar defects along the c{sub h}-axis (stacking direction of the hexagonal close-packed planes) of parent rhombohedral R3-bar m cell. Such stripe structures become faint with increasing x, Co content. The origin of the planar defects is mainly attributed not to the different structures but to the different local orientations of the monoclinic LMCO. Local disordering of Li and (Mn,Co) in (Li,Mn,Co) planes is developed with increasing x and the structures are transformed from C2/m to R3-bar m. The alternative (Li,Mn,Co)-plane stacking structure, trigonal P3{sub 1}12 LMCO, was occasionally observed. However, only P3{sub 1}12 LMCO platelets with a thickness of a single unit cellmore » were detected. - Graphical abstract: An HREM image for Li{sub 1.95}(Mn{sub 0.9}Co{sub 0.15})O{sub 3} and schematic drawings of C2/m and P3{sub 1}12 Li{sub 2}MnO{sub 3} projected along the various zone axes. Each projected unit cell is indicated by rectangles and parallelograms . - Highlights: • Li{sub 2−δ}(Mn{sub 1−x}Co{sub x}){sub 1+δ}O{sub 3} was studied by high-resolution electron microscopy (HREM). • HREM studies revealed a large amount of planar defects in C2/m Li{sub 1.95}Mn{sub 0.9}Co{sub 0.15}O{sub 3}. • The origin of the defects is the different local orientations of the C2/m platelets. • P3{sub 1}12 platelets with only single unit cell sequence were detected.« less

Polycrystalline FeSr 2 YCu 2 O 6 + y was synthesized and its transport and magnetic properties were studied. Diamagnetism was observed below 60 K. Zero resistivity was observed below 38 K under zero magnetic field and below 10 K under 160 kOe. A two-step transition was observed in resistivity measurement due to the superconductivity in individual grains and across inter-grain boundaries. The critical current density in individual grains, J c intra , at 2 K under 1 kOe was deduced 3.4 × 105 A/cm2 from the Bean model. In contrast, the critical current density in inter-grain boundaries, J c inter , at 2 K was 1.7 A/cm2 in voltage–current measurement. The two-step transition seems to result from the large difference between J c intra and J c inter .

To investigate vortex states in exfoliated Bi2Sr2CaCu2O8+y high-Tc superconductor with and without micro-hole arrays, the in-plane resistance in the vortex states has been measured. In exploration of vortex-lattice melting transition in pristine films, signs of the transition have been successfully found in the films as thin as a few hundred nm. A comparison of irreversibility lines in both samples indicates that influence of artificial micro holes is masked at low temperatures due to the native residual pinnings.

In order to study the mechanism of phase transformation from Bi-2212 to Bi-2223, we fabricated Pb-Ca-Cu deposited Bi-2212 (001) single crystals as precursors of the Bi,Pb-2223 phase. These single crystals were heated in a sintered Bi-Pb-Sr-Ca-Cu-O pellet, and microstructure was observed by analytical electron microscopy. As a result of the microstructural observation around the Bi,Pb- 2223 phase, two formation paths of Bi,Pb-2223 were recognized. One is the formation from a liquid phase which is formed by Bi- 2212 and melting of the secondary phases such as (Ca,Sr)2PbO4 and CuO. The other is the growth of Bi,Pb-2223 into Bi-2212 phase by diffusion of Pb, Ca and Cu atoms along the hk 0> directions of Bi-2212.

Vortices (magnetic flux quanta) in the superconducting networks perforated with anti-dots (holes) arrays behave as electrons in atomic lattice of crystals. Repulsive and attractive interaction among vortices and anti-dots resemble to those among electrons and atoms in crystals. To confirm the variety of the vortex physics similar to the solid state physics, we have fabricated such superconducting networks with antidots array in metallic, inter-metallic and high-T c superconductors (HTSCs), and have measured magneto-resistance of vortex-flow. In these materials, we have observed integer-matching at the matching fields and fractional-matching effect between them. Most of them are well explained by commensurability between Abrikosov vortex lattice and anti-dots array. Furthermore, the effect of the anti-dots array in HTSCs appears as another kind of phase transitions instead of to the first-order melting transition of vortex lattice in pristine samples.

We have performed scanning tunneling microscopy on Fe1.07Te that is the parent compound of the iron-chalcogenide superconductors (SCs). The results indicate the existence of the unidirectional electronic order with a period of a 0 (a 0 interchalcogen distance) along one Te–Te direction. From the one-dimensionality of the electronic order, it is believed that the structural or antiferromagnetic transition is closely related to the formation of this electronic order. The results in this study will be crucial key in understanding the parent state of iron-chalcogenide SCs.

To study the vortex states in Bi2Sr2CaCu2O8+y (Bi2212) high- T c superconductor with periodic array of antidots, we have measured the c -axis critical current in a stack of the intrinsic Josephson junctions with a square lattice of antidots, which gives us information on the c -axis correlation of the pancake vortices. Without the antidot array, the c -axis critical current can probe the first-order vortex lattice melting transition. Additionally, a suppression of the critical current in the vicinity of zero magnetic field is found, which may be related to the instability of vortex lattice under the parallel current flow. With the square lattice of antidots, enhancements of the critical current due to the matching effect are observed in both the integer and fractional matching fields. By mapping the critical current on H - T diagram, the influence of the matching effect on the phase boundary of vortex solid and liquid is shown.

We have tried self-flux and pulsed laser deposition (PLD) method to make single crystals of RuSr2GdCu2O8. In the self-flux method, we added the excess optimum solvent (Ru:Gd:Cu = 0.8:0.4:1.7) during growth under a low cooling rate of 1.5iC/hr. But, we could not find any single crystals. In the PLD method, we found the growth condition of single crystal phase with substrate temperature (∼800 °C) and substrates (SrTiO3).

A manganese-based solid solution with the composition of Li1.95Mn0.9Co0.15O3 was synthesized by a simplified coprecipitation method, followed by a combustion technique, and its electrochemical characteristics as a lithium-battery cathode were investigated. Rietveld refinement based on neutron diffraction data revealed that the material is assigned to an Li2MnO3-type structure model with a monoclinic cell due to the space group symmetry of C2/m. In cycling of the Li/Li+/Li1.95Mn0.9Co0.15O3 cell in the potential range of 2.0-4.8 V at current densities of 30 mAg(-1), the discharge capacity characteristically increases from 46.3 to 196.5mAhg(-1) as the cycle increases from 1 to 11, and a discharge capacity of > 175.5 mAhg(-1) is obtained between the 23rd and 58th cycles with small capacity fading of 2.41%. The results of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) measurements showed that the manganese redox reaction (Mn3+/Mn4+) in the Li1.95Mn0.9Co0.15O3 system is progressively activated during the first ten-odd cycles, following continuous occurrence of the extraction of oxygen molecules from the electrode material over these charge processes. It could be assumed that such behaviors significantly influence the electrochemical characteristics of the Li1.95Mn0.9Co0.15O3 system. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.079203jes] All rights reserved.

FeSr2YCu2O6+δ (Fe1212) shows superconductivity only after proper annealing in N2 flow, subsequently, annealing in O2 flow and under high O2 pressure. In order to optimize each of the annealing temperature for superconductivity, Fe1212 samples were annealed at various temperature in each annealing process. The optimized annealing condition is annealing in N2 flow at 790 °C, annealing in O2 flow and under high O2 pressure at 270 °C. The resistance began to decrease at 64 K and dropped to zero at 40 K. Superconductivity of Fe1212 was affected by temperature of N2 annealing process rather than that of O2 annealing. The N2 annealing affects the offset superconducting transition temperature rather than the onset superconducting transition temperature. This implies the inter-grain superconductivity in ceramic Fe1212 is affected by N2 annealing temperature.

To explore vortex states and their dynamics in superconductors with large thermal fluctuation and artificial pinning potentials, we have studied the influence of periodic arrays of antidots in high- T c superconductor Bi 2 Sr 2 CaCu 2 O 8+ y (Bi2212). The diameter dependence of the matching effect in Bi2212 without a change of the thickness and oxygen doping level was investigated using one Bi2212 single-crystal film of homogeneous thickness in which several different-diameter antidot arrays were introduced. The matching effect observed by vortex-flow resistance measurements changed systematically depending on the diameter. The antidot-diameter dependence of the irreversibility lines was examined.

We have performed scanning tunneling spectroscopy on a single crystal of Bi2Sr2Ca(Cu1−x Zn x )2O8+δ (x=0.005) and found several regions where at least two Zinc (Zn) impurities aggregate within a few nm. In these regions, there are two-dimensional local density-of-states (LDOS) modulations with the period of about 1.41a 0 (a 0 is Cu–O–Cu distance) along the direction tilted 45° from Cu–O–Cu direction within the energy of below 10 mV. Since these modulations are suppressed in a map of the ratio between LDOS at a positive energy and at its negative, it is presumable that these modulations do not stem from the simple quasiparticle interference whose pattern should be enhanced in the ratio map. We suggest the possible explanations with respect to the origin of the observed modulations.

酸素が重要な役割を果たしている酸化物高温超伝導体の研究において，中性子回折による結晶構造解析は必須である。これまでに発見された多数の酸化物高温超伝導体の結晶構造が中性子回折により明らかにされ，それを基盤にして物質設計の指針が構築され，さらなる物質探索が展開されている。また，中性子回折により明らかにされた結晶学的な情報は，酸化物高温超伝導体の特徴ある物性を解明する研究の基盤となっている。

Heavily Fe-substituted Ba 2 YCu 3 O 6+ δ -type compound FeSr 2 YCu 2 O 6+ δ exhibits superconductivity around 60 K, only when it is annealed in N 2 and subsequently in O 2 . Cationic distribution in this compound is strongly dependent on ionic radius at the Y site, and its superconducting properties are affected by the cationic distribution. In contrast, although the compound with the substitution of fluorite-type unit for Y has cationic order, it does not exhibit superconductivity. We have analyzed the crystal structure of the compounds with the substitution of other lanthanoid elements for Y and with substitution of fluorite-type unit for Y.

The magnetic superconductor FeSr2YCu2O6+y exhibits superconductivity below 59 K, only when it is properly annealed in a N2 flow and subsequently annealed in an O2 flow and under high O2 pressure. FeSr2LnCu2O6+y (Ln = Nd, Eu, Gd and Tb), where Ln is substituted for Y, was also studied. While FeSr2GdCu2O6+y and FeSr2EuCu2O6+y show superconductivity below 37 K and 31 K, respectively, FeSr2NdCu2O6+y and FeSr2TbCu2O6+y do not show superconductivity. A peak was observed at 20 K in the temperature dependence of susceptibility under a magnetic field of 1 T for FeSr2YCu2O7.65, and this implies the magnetic order of the Fe ion. To study the magnetism of the Fe ion in FeSr2YCu2O7.65, non-superconducting FeSr2Y(Cu0.95Zn0.05)2O7.65 was studied. The magnetism of the Fe ion is mainly antiferromagnetic.

To explore the vortex ratchet effect in underlying spatially asymmetric potentials in high-Tc superconductors, we have measured vortex-flow and rectification resistance in Bi2Sr2CaCu2O8 + y (Bi2212) single-crystal films with an array of triangular holes fabricated using focused ion beam. The matching effect was observed in vortex-flow resistance in the sample with the array of triangular holes as well as that with the symmetric antidots arrays. In addition to that, we found a rectification effect in this sample. Multiple reversals of the rectification direction reflecting the net motion of vortices were observed as the magnetic field changes. In contrast to the vortex ratchet effects observed in conventional superconductors, the sign of the rectification sharply flipped in the matching fields.

FeSr2YCu2O6+δ with tetragonal Ba2YCu3O6+δ-type structure exhibits superconductivity around 60 K, only when it is annealed in reduced atmosphere and subsequently in oxidized atmosphere. However, FeSr2NdCu2O6+δ with the substitution of lanthanoid with large ionic radius for Y do not exhibit superconductivity even if it is annealed in the same process as superconducting FeSr2YCu2O6+δ. We have performed neutron powder diffraction of the FeSr2Y1−xNdxCu2O6+δ solid solution system to investigate the effect of the Nd substitution on structure and superconductivity. The structure analysis indicates that the disorder of Sr and Nd, of oxygen on double superconducting CuO2 sheets and of Cu and Fe prevents exhibiting superconductivity in the Nd-substituted system.

Superconductivity in two Li-containing compounds of Li2Pd3B and Li2Pt3B was recently discovered. These materials, showing the superconducting transition at 7.2 K and 2.6 K, respectively, have the same cubic structure (P4332) composed of distorted octahedrons without mirror or inversion symmetry along any directions. This is a very interesting feature of those materials in relation to the symmetry of superconductivity. Resistivity measurements in magnetic fields gave their upper critical fields, Hc2(0) = 45 kOe and 19 kOe, respectively. Their specific heat was measured using a heat-pulse relaxation method. The Sommerfeld coefficient (γ) and Debye temperature (θD) terms of Li2Pd3B were given as γ=9.5 mJmol-1K-2 and θD=228 K . The value of C/γT at Tc was calculated to be 1.7. In the same manner, those parameters were described for Li2Pt3B as γ=9.6 mJmol-1K-2, θD=240 K, and C/γTc =0.75, respectively. Since C/γTC in the weakcoupling limit by the BCS theory is 1.43, the value of 1.7 for Li2Pd3B is slightly higher. The electronic specific heat of Li2Pd3B at a zero magnetic field follows the typical exponetial behavior discribed in the BCS theory, while that of Li2Pt3B shows quadratic behavior. This result suggests the line nodes exist in the superconducting gap of Li2Pt3B driven by the spin-orbit interaction.

There are many ternary intermetallic compounds with BaAl 4 -type and its derivative structures. LaPd 2 Ge 2 is already known as one of the BaAl 4 -type superconductors with T c of 1.12 K. We have synthesized a new intermetallic compound La 3 Pd 4 Ge 4 with higher T c of 2.75 K than that of LaPd 2 Ge 2 , which had the structure with the insertion of the AlB 2 -type layer in LaPd 2 Ge 2 . A detailed crystal structure analysis of La 3 Pd 4 Ge 4 was carried out by neutron powder diffraction because it is useful to the analysis of small interplanar spacing. The neutron diffraction study indicates that La 3 Pd 4 Ge 4 has U 3 Ni 4 Si 4 -type structure with a lower symmetry than that of LaPd 2 Ge 2 , and the typical interatomic distances of La 3 Pd 4 Ge 4 are shorter than those of LaPd 2 Ge 2 . The coordination of Pd to three Ge in the AlB 2 -type layer of La 3 Pd 4 Ge 4 is characteristic, which is not stabilized in other lanthanide-substituted intermetallics Ln 3 Pd 4 Ge 4 (Ln = Y, Gd–Yb).

To investigate vortex dynamics in Bi 2 Sr 2 CaCu 2 O 8+ y singlecrystalline thin films with regular holes array, we have already studied the vortex-flow resistance in various samples which have triangular, square, and randomly distributed holes arrays. A matching effect has been observed in the vortex-flow resistance in samples with the regular holes arrays. In addition to them, we measured the vortex-flow resistance, the critical current, and I – V characteristics in a sample with a regular surface structure of ∼30 nm depth. It is found that even that kind of the small surface structure induces the remarkable matching effect in the vortex liquid as well as the vortex solid.

We have reported the crystal structure of the superconducting systems Y2C3 and Li2Pd3B without inversion symmetry. The structure of Y2C3 has the dumbbell-like C-C unit occupying polyhedrally-coordinated void, while the structure of Li2Pd3B has three-dimensional framework of the BPd6 octahedron, which exists at the clearance gap of the Li partial structure. The superconducting transition temperature is strongly dependent on the structural change of the C-C distance in the Y2C3 system and of the distortion of the BPd6 octahedron in the Li2Pd3B system.

We have investigated correlation between structural and electronic anisotropies in a parent compound of Fe-chalcogenide superconductor ${\mathrm{Fe}}_{1+\ensuremath{\delta}}\mathrm{Te}$ with $\ensuremath{\delta}=0.09$ by means of synchrotron x-ray diffraction and in situ in-plane resistivity anisotropy measurements with uniaxial stress applied along a tetragonal $a$ axis. This system is known to exhibit a tetragonal-to-monoclinic structural transition at ${T}_{\mathrm{S}}\ensuremath{\sim}60$ K. We have confirmed that the in-plane resistivity anisotropy in the low-temperature monoclinic phase is attributed to the asymmetry in volume fractions of the monoclinic domains, as was suggested in a previous study [Jiang et al., Phys. Rev. B 88 115130 (2013)]. On the other hand, we found another in-plane resistivity anisotropy above ${T}_{\mathrm{S}}$. The present x-ray diffraction and resistivity anisotropy measurements have revealed that this anisotropy is not due to an onset of the low-temperature monoclinic phase but to the lattice softening enhanced toward ${T}_{\mathrm{S}}$. As one of the possibilities, we suggest that the orbital fluctuation contributes to the lattice softening and the resistivity anisotropy above ${T}_{\mathrm{S}}$.

The vortex-lattice melting transition of a limited number of vortices confined in mesoscopic square superconductors was studied by $c$-axis resistance measurements using stacks of intrinsic Josephson junctions in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+y}$. In contrast to the melting transition in bulk crystals, we have first found a clear oscillatory behavior in the field dependence of the melting temperature in small samples of $5--10\text{ }\text{ }\ensuremath{\mu}m$ square. The periods of the oscillations roughly obey the regularity of the matching conditions of square vortex lattices surrounded by a square boundary and the melting temperatures are enhanced around the vortex number of ${i}^{2}$ (where $i$ is an integer). The results suggest that a confinement effect by the square boundary stabilizes square lattice structures which are realized around ${i}^{2}$ vortex number even in competition with the favorable Abrikosov triangular lattice in the bulk.