Yasuko Matsui

New series of oxysulphate superconductors (Cu0.5S0.5)Sr2Can−1CunOy (n = 37), prepared at high pressure

Abstract A new series of oxysulphate superconductors, (Cu 0.5 Sr 0.5 )Sr 2 Ca n −y O y was prepared at high pressure of 6 GPa and 1250°C. Five members with n = 37 were obtained in bulk. They show superconductivity with T c ranging from ≈ 60 K for n = 7 to 100 K for n = 3. HRTEM and electron diffraction observation for each member indicated an ordered arrangement of Cu and S in a (Cu,S) plane resulting in a superstructure with a s = 2 a , b s = b , c s = 2 c or a s = 2 s , b s = b , c s = c with respect to a basic tetragonal lattice, a , b , c . Local intergrowths of phases with various n values up to 13 were also observed.

A new oxycarbonate superconductor (Cu0.5C0.5)2Ba3Ca2Cu3O11 (Tc=91 K) prepared at high pressure

Abstract We prepared a new oxycarbonate superconductor, (Cu 0.5 C 0.5 ) 2 Ba 3 Ca 2 Cu 3 O 11 at 1250°C under 5 GPa. This phase is the m =2 and n =3 member of a homologous series, (Cu 0.5 C 0.5 ) m Ba m +1 Ca n -1 Cu n O 2 m +2 n +1 reported previously. Its X-ray pattern could be indexed assuming a tetragonal subcell with a =3.852(1), c=18.61(2) A . Electron microscopic observations indicated ordering between Cu and C in the (Cu, C) plane, resulting in a superlattice, a s =2 a , b s = b and c s =2 c with respect to the tetragonal subcell. This new member showed a superconducting transition at 91 K.

Synthesis, crystal structures and superconductivity of new copper oxyfluorides, Sr2RCu2O5F (R = Y,La,Nd,Sm,Gd,Dy,Er and Yb)

Abstract A new series of oxyfluoride compounds, Sr2RCu2O5F (R = Y,La,Nd,Sm,Gd,Dy,Er and Yb), was successfully synthesized under high pressure of 6 GPa. Electron microscopic observation and X-ray Rietveld analysis indicated that they are essentially isostructural to La2SrCu2O6 (tetragonal, 14/mmm) with a half of apical oxygen sites of CuO5 pyramids replaced by F atoms. Superconductivity occurred in the Nd analogue after Ca substitution for x ≥ 0.5 in Sr2Nd1−xCaxCu2O5F. single-phase sample of the Nd analogue was obtained at x = 0.8 having the highest Tc of 85 K with a Meissner fraction of 6.8% and a shielding fraction of 7.4% at 5 K. These small fractions suggest a small grain size, weak intergrain coupling and/or weak pinning force.

Homologous series of high-Tc superconductors (Cu,C)Sr2Can−1CunOy (n=2,5) and (Cu,N,C)Sr2Can−1CunOy (n=3–6) synthesized under high pressure

Abstract The Sr–Ca–Cu–C–O and Sr–Ca–Cu–N–C–O systems were investigated under high pressure/high temperature conditions. The former includes (Cu,C)Sr 2 Ca n −1 Cu n O y [(Cu,C)-12( n −1) n -Sr, n =2,5] phases, the latter, (Cu,N,C)Sr 2 Ca n −1 Cu n O y [(Cu,N,C)-12( n −1) n -Sr, n =3–6] phases. In the former series, the n =3,4 members could not be synthesized in bulk form. A small level of nitrogen-doping was found to be highly effective in stabilizing the members with n =3–6. All these phases present superconductivity, with the highest T c of 113 K in (Cu,N,C)-1234-Sr. Two-types of superstructures with 4 a × b ×2 c and 2 a × b ×2 c were observed in the phases with n ≤4, depending on the system and n -value.

Superconductivity in Sr(Ln)NbO system (Ln:La,Nd,Pr,Ce,Gd and Ho)

Abstract A new non-Cu oxide superconductor Sr(Ln)NbO system (Ln:La,Nd,Pr,Ce,Gd and Ho) has been found by the resistivity and magnetization measurements. The highest onset transition temperature is about 12K. Preliminary electron and X-ray diffraction experiments indicate that main phase (∼90%) in this system is (Sr 1− x Ln x )Nb 2 O 6−gd and another impurity phase (∼10%) is (Sr 1− x Ln x )Nb 2 O 7−δ , suggesting that the basic crystal structure is probably an oxygen deficient CaTa 2 O 6 type structure.