[en] The electron-doped bismuth oxide (Ba_0.6Bi_0.4)BiO_2.92 has been successfully synthesized by the two-step heating method. Mixed powders of the starting materials have been pelletized and heated in flowing gas of N₂ at 800 deg. C for 12 h. The reacted pellets have been heated at 400 deg. C first in flowing gas of O₂ for 24 h and then under a high oxygen-pressure of 600 atm at 400 deg. C for 96 h. It has crystallized in a pseudo-cubic symmetry. From the X-ray diffraction and inductively coupled plasma analyses, the substitution of Bi for Ba has been confirmed, but the product has still remained an insulator

[en] Highlights: • First superconductor in the Nb-1212 system with the Y-123 type structure is discovered. • Hole-doping is carried out through the partial substitution of Sn⁴⁺ for Nb⁵⁺. • T_c of EuSr₂Cu₂Nb_0.8Sn_0.2O_8−y is about 40 K. -- Abstract: We have successfully synthesized new superconductor EuSr₂Cu₂Nb_1−xSn_xO_8−y of the so-called Nb-1212 system, where Nb is substituted for Cu1 in the RE-123 (RE = rare earth elements) type structure by the hole-doping through the partial substitution of Sn⁴⁺ for Nb⁵⁺. The highest value of the superconductivity of the superconducting transition temperature, T_c, is about 40 K at x = 0.2. This is the first superconductor in the Nb-1212 system

[en] Anisotropic properties of the single crystal Pb₂Sr₂Ho_0.5Ca_0.5Cu₃O₈ have been investigated by measuring the electrical resistivity in the ab-plane ρ_ab(H, θ, T), which depends on the angle θ between the ab-plane and the magnetic-field direction, in various constant fields H perpendicular to the current direction. All the angle-dependent values of ρ_ab(H, θ, T) at a constant temperature are scaled to be on one curve as a function of reduced field. The anisotropic parameter γ triple-bond (m_c*/m_ab*)^1/2 is estimated as 12-13, which is larger than that of YBa₂Cu₃O₇ and much smaller than that of Bi₂Sr₂CaCu₂O₈. It has been concluded that the anisotropy does not always depend on the thickness of the blocking layer but seems to depend on the overlap of the electronic wave functions along the c-axis. Anisotropy in the pinning potential has also been discussed from the resistive tail in the temperature dependence of ρ_ab(H, θ, T)

[en] Our recent works on the low-temperature synthesis of oxide superconductors using molten salts are reviewed. We have succeeded in preparing insulating La₂CuO₄ and La_2-x Sm_x CuO₄ with the Nd₂CuO₄-type(T') structure and superconducting (Ba, K, Rb) BiO₃ by the direct precipitation from molten alkaline-metal hydroxides at a low temperature as low as 260-400degC. (author)

[en] Li-intercalated layered perovskites Li_xAB₂Na_n-3Nb_nO_3n+1 (A=K, Rb, Cs; B=Ca, Sr, Ba) with n=3 and 4 have been prepared by an electrochemical technique. For the Li_xAB₂Nb₃O₁₀ superconducting materials, the value of T_c has been found to increase up to about 5-6 K as the a-axis length increases. For Li_xCsBa₂Nb₃O₁₀ with the largest a-axis length, however, superconductivity does not appear. In addition, Li_xKCa₂NaNb₄O₁₃ shows no superconductivity

[en] Highlights: • First superconductor in the Ta-1212 system with the Y-123 type structure is discovered. • Hole-doping is carried out through the partial substitution of Sn⁴⁺ for Ta⁵⁺. • T_c of EuSr₂Cu₂Ta_0.8Sn_0.2O_8−y is about 40 K. - Abstract: We have successfully synthesized a new superconductor EuSr₂Cu₂Ta_1−xSn_xO_8−y of the so-called Ta-1212 system, where Ta is substituted for Cu(1) in the Y-123 type structure and holes are doped into the CuO₂ plane through the partial substitution of Sn⁴⁺ for Ta⁵⁺. The superconducting transition temperature, T_c, is about 40 K at x = 0.2. This is the first superconductor in the Ta-1212 system

[en] Highlights: • A_x(C₂H₈N₂)_yFe_2−zSe₂ (A = Li, Na) with T_c = 45 K has been synthesized. • The c-axes of A_x(C₂H₈N₂)_yFe_2−zSe₂ (A = Li, Na) are as long as about 21 Å. • T_c decreases with increasing post-annealing temperature. • T_c of intercalated FeSe rises with increasing distance between the neighboring Fe layers. • T_c of intercalated FeSe tends to be saturated at about 45 K. - Abstract: New iron-based intercalation superconductors A_x(C₂H₈N₂)_yFe_2−zSe₂ (A = Li, Na) with T_c = 45 K have successfully been synthesized via intercalation of dissolved alkaline metal in ethylenediamine. The c-axis lengths of A_x(C₂H₈N₂)_yFe_2−zSe₂ (A = Li, Na) are 20.74(7) Å and 21.9(1) Å, respectively, and are about 50% larger than that of K_xFe₂Se₂, indicating that not only alkaline metal but also ethylenediamine is intercalated between the Se–Se layers of FeSe. It seems that the high-T_c of A_x(C₂H₈N₂)_yFe_2−zSe₂ (A = Li, Na) is caused by the possible two-dimensional electronic structure due to the large c-axis length. Through the post-annealing in an evacuated glass tube, it has been found that T_c decreases with increasing post-annealing temperature and that deintercalation of EDA from the as-intercalated sample takes place at low temperatures below 250 °C

[en] We have investigated the relation between the crystal structure and superconductivity in La_1.9Bi_0.1CuO_4+δ, in which the phase separation observed in La₂CuO_4+δ is suppressed. A phase diagram in the T δ plane is given for La_1.9Bi_0.1CuO_4+δ with excess oxygen. For very small δ values, the crystal structure is orthorhombic, and an orthorhombic tetragonal phase transition occurs markedly at δ approximately 0.03 in the measured temperature range between 13 and 293 K. Superconductivity is observed in the range of 0.04 approx-lt δ approx-lt 0.11. This is clear evidence that high-Tc superconductivity also appears in the tetragonal phase. 5 refs., 2 figs

[en] Using the solvothermal method, we have successfully synthesized new MoSe₂-based intercalation superconductors A_x(C₂H₈N₂)_yMoSe₂ (A = Ca, Sr, Ba; x = 1) with T_c = 6.0, 6.4, and 7.2 K, respectively, through the co-intercalation of alkaline-earth metals and ethylenediamine into semiconducting 2H-MoSe₂. It has been concluded that the T_c values in the MoSe₂-based intercalation superconductors are clearly related to the electronic density of states (EDOS) at the Fermi level. Moreover, it has been found that the T_c value increases with increasing ionic radius of A in A_x(C₂H₈N₂)_yMoSe₂ (A = Ca, Sr, Ba; x = 1), which is speculated to be due to the increase in the a-axis length and the resulting increase in the EDOS at the Fermi level. The solvothermal method is useful for the synthesis of both alkaline-earth metal- and organic molecule-intercalated superconductors. (author)

[en] The electronic specific heat of as-grown and annealed single-crystals of FeSe_1-xTe_x (0.6 ≤ x ≤ 1) has been investigated. It has been found that annealed single-crystals with x = 0.6-0.9 exhibit bulk superconductivity with a clear specific-heat jump at the superconducting (SC) transition temperature, T_c. Both 2Δ₀/k_BT_c [Δ₀: the SC gap at 0 K estimated using the single-band BCS s-wave model] and ΔC/(γ_n - γ₀)T_c [ΔC: the specific-heat jump at T_c, γ_n: the electronic specific-heat coefficient in the normal state, γ₀: the residual electronic specific-heat coefficient at 0 K in the SC state] are largest in the well-annealed single-crystal with x = 0.7, i.e., 4.29 and 2.76, respectively, indicating that the superconductivity is of the strong coupling. The thermodynamic critical field has also been estimated. γ_n has been found to be one order of magnitude larger than those estimated from the band calculations and increases with increasing x at x = 0.6-0.9, which is surmised to be due to the increase in the electronic effective mass, namely, the enhancement of the electron correlation. It has been found that there remains a finite value of γ₀ in the SC state even in the well-annealed single-crystals with x = 0.8-0.9, suggesting an inhomogeneous electronic state in real space and/or momentum space. (author)