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High-pressure synthesis of perovskite-derived compounds in the Sr-Y-Cu-O system
Three perovskite-derived compounds were found in the Sr-Y-Cu-O system treated at 1.6 GPa. These are Sr3Cu8O2, Sr3.5Y1.5Cu3O2 and Sr4Y3Cu4O14. These compounds are high-pressure phases crystallized in orthorhombic structures. The stabilities of the new compounds depended highly on oxygen pressure. The non-superconducting orthorhombic phase Sr2YCu3O2 was also discovered: It was obtained at a relatively low oxygen pressure. Magnetic susceptibility measurements have revealed that the superconducting transition temperature of Sr2YCu3O2 decreased on lowering the oxygen content.
Ono Akira
(1992)
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Synthesis, crystal structures and superconductivity of new copper oxyfluorides, Sr2RCu2O5F (R = Y,La,Nd,Sm,Gd,Dy,Er and Yb)
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, I4/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. A 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.
Isobe,Li,Matsui,Izumi,Kanke,Takayama-Muromachi
p. 5 - 14
(1996)
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New series of high-Tc superconductors AlSr2Can-1CunO2n+3 (n = 4, Tc = 110 K; n = 5, Tc = 83 K) prepared at high pressure
A new series of high-Tc superconductors AlSr2Can-1CunO2n+3 (Al-12(n - 1)n) was prepared at high pressure of 5.5 GPa and 1250°C, whose members are the first superconductors including Al as a main component. Two members with n = 4, 5 were obtained in bulk and the former showed superconducting transition at 110 K while the latter at 83 K. They had tetragonal cells with a = 3.839(1), c = 17.72(1) angstrom for n = 4 and a = 3.845(1), c = 20.87(1) angstrom for n = 5. HRTEM observations indicated that they are essentially isomorphous with the Tl (or Hg)-based superconductors, Tl (Hg)-1234 and 1245, respectively. Significant intergrowths of phases with different n values up to n = 8 were observed in Al-1245.
Isobe,Kawashima,Kosuda,Matsui,Takayama-Muromachi
p. 120 - 126
(1994)
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High-pressure synthesis and physical properties of ruthenate-cuprates RuSr2LnCu2O8 (Ln = Y, Dy, Ho, Er)
We report the series of ruthenate-cuprates RuSr2LnCu 2O8 (Ru-1212Ln; Ln = Y, Dy, Ho, Er), which were prepared at 1200-1300 °C under 6 GPa. High-purity sample could be obtained for every system with the 'Ru-poor' starting composition, Ru0.9Sr 2LnCu2O7.8. It was confirmed that a solid solution of (Ru1-xCux)Sr2YCu2O y exists and its range terminates at x ～ 0.1 without formation of the stoichiometric phase of RuSr2YCu2Oy. Many Y-based samples were prepared varying the Ru/Cu ratio and the oxygen contents. According to DC susceptibility measurements, ferromagnetism and superconductivity looked to coexist below approximately 40 K in some samples. However, DC resistivity was always quite high even when a sample showed a large diamagnetism in a low temperature region. These results may suggest phase separation regarding the Ru/Cu ratio in the solid solution of (Ru 1-xCux)Sr2YCu2Oy, casting doubt for the coexistence of superconductivity and ferromagnetism.
Kawashima,Takayama-Muromachi
p. 85 - 94
(2003)
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High-pressure synthesis and magnetic properties of the niobio-cuprate Nb0.9Sr2HoCu2.1O7.9
Ho-based 1212 niobio-cuprate (Nb-1212Ho) was synthesized for the first time. An off-stoichiometric starting composition Nb0.9Sr2HoCu2.1O7.9 led a phase-pure polycrystalline sample under the synthesis condition at 1450 °C for 2 h at 6 GPa, approximating the true bulk composition. X-ray diffraction pattern clearly indicated an Nb-1212 type structure for the compound with lattice parameters a = b = 3.8505(1) A? and c = 11.574(3) A?, suggesting that the space group P4/mmm is likely for the structure. Unlike Nb-1212Y, the Nb-1212Ho compound showed neither superconductivity nor a magnetic order down to 1.8 K. A relatively large magneto-resistance approximately -7% was found at 30 K.
Balamurugan,Yamaura,Takayama-Muromachi
p. 1206 - 1209
(2008)
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Superconductivity in the series of compounds Sr2Can-1CunOy (n = 1 approx. 4) prepared under high pressure
A series of compounds Sr2Can-1CunOy (n = 1-4) were prepared under 5-6 GPa and their superconducting properties were examined. The n = 1 member of the series, Sr2CuO3+δ, has been believed as a superconductor with Tc of 70 K. However, our experiments suggest strongly that it is not superconducting but the 70 K superconductivity is ascribed to the n = 2 member of the series, Sr2CaCu2Oy. The n = 3 and 4 members were also prepared and they were confirmed to have Tc's of 109 and 83 K, respectively.
Kawashima,Takayama-Muromachi
p. 106 - 112
(1996)
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High-pressure synthesis of the zero-charge-reservoir 0223 superconductor in the Sr-Ca-Cu-O system
We have refined the high-pressure synthesis of the zero-charge-reservoir 0223 phase of the Sr-Ca-Cu-O system. Samples were prepared from three different starting cation compositions of Sr2CaCu2O6+y, Sr2Ca2Cu3O8+y and Sr2Ca3Cu4O10+y. The amount of oxygen, y, was controlled by using different amounts of SrO2 in the starting material mixture. With SrO2 of commercial grade, two types of HRTEM images were observed for the a-b plane: one with a double periodicity and another with no periodicity. TEM-EELS analysis revealed that the former was due to carbonate inclusions. Using freshly synthesized SrO2, crystalline samples with Tc ≈ 110 K were obtained. The samples showed body-centered symmetry in ED patterns, being thus of the 0(Sr)2(Ca)23 phase. The actual amount of oxygen in the obtained samples as determined by wet-chemical analysis was found considerably lower than the nominal value. However, the wet-chemical analysis revealed a much higher oxidation state for the 0(Sr)2(Ca)23 phase than generally expected for a high-Tc superconductor.
Ushiki, Masako,Motohashi, Teruki,Yamauchi, Hisao,Karppinen, Maarit
p. 167 - 172
(2002)
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New series of oxide superconductors, BSr2Can-1CunO2n+3 (n = 3 approx. 5), prepared at high pressure
Recently, a new oxyborate superconductor with Tc = 110 K, BSr2Ca3Cu4O11, was prepared under high pressure [E. Takayama-Muromachi et al., Physica C 241 (1995) 137]. This phase is thought to be the n = 4 member of a homologous series, BSr2Can-1CunO2n+3. In this paper, we report new members of the series, BSr2Ca2Cu3O9 (n = 3) and BSr2Ca4Cu5O13 (n = 5), which were prepared under 6 GPa. These members showed Tc's of 75 K and 85 K, respectively. Their X-ray powder diffraction patterns could be indexed assuming tetragonal cells with a = 3.821(1), c = 13.854(6) angstrom for n = 3 and a = 3.837(2), c = 20.22(1) angstrom for n = 5. HRTEM observations indicated that they are essentially isomorphous with Tl(or Hg)-1223 and 1245.
Kawashima, T.,Matsui, Y.,Takayama-Muromachi, E.
p. 131 - 136
(1995)
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New oxyfluoride superconductors Sr2Can-1CunO2n+δF2±y (n = 2; Tc = 99 K, n = 3; Tc = 111 K) prepared at high pressure
We prepared new oxyfluoride superconductors, Sr2CaCu2O4+δF2±y and Sr2Ca2Cu3O6+δF2±y, at 1250 °C under 5.5 GPa. These phases are the n = 2, 3 members of a homologous series, Sr2Can-1CunO2n+δF2±y, respectively, in which the n = 1 phase was reported previously. X-ray and HRTEM studies indicated that they have tetragonal structures with a = 3.843(1), c = 19.88(1) angstroms for n = 2 and a = 3.840(1), c = 26.17(1) angstroms for n = 3. The n = 2 phase showed a superconducting transition at 99 K, while the n = 3 one at 111 K.
Kawashima,Matsui,Takayama-Muromachi
p. 313 - 320
(1996)
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Reactions of Pulsed-Laser Evaporated Ca, Sr, and Ba Atoms with O2. Infrared Spectra of the Metal Oxides, Oxide Dimers, Dioxides, and Peroxides in Solid Argon
Pulsed-laser ablated Ca, Sr, and Ba atoms have been reacted with O2 in excess argon during condensation at 10 K.Infrared spectra and oxygen isotopic substitution show that the major products are the symmetrical OMO metal dioxide and the rhombic metal oxid
Andrews, Lester,Yustein, Jason T.,Thompson, Craig A.,Hunt, Rodney D.
p. 6514 - 6521
(2007/10/02)