High-pressure and high oxygen-pressure syntheses of oxide superconductors

Abstract

We report high-pressure and high-oxygen pressure syntheses of various oxide superconductors. Several new oxycarbonate superconductors were discovered in the CaBaCuCO system at 5 GPa. They are (Cu 0.5C 0.5)Ba 2Ca n−1Cu nO 2n+3 (n=3; Tc=67 K, n=4; Tc=117 K) and (Cu 0.5C 0.5) 2Ba 3Ca n−1Cu nO 2n+5 (n=4,5; Tc≈113 K). The former series of compounds are essentially isomorphous to Tl (or Hg)−12(n−1)n, n=3,4, respectively. On the contrary, no compounds corresponding to the latter have been known. An “infinite-layer” sample was prepared at 6 GPa by adding CaCO 3 and SrCO 3. HRTEM observation for this sample suggested that it included defect layers, (C,Cu)Oy which may be responsible for ∼100 K superconductivity. Finally, Ga- and Al-based 1212 phases prepared under high pressure are discussed.