New Series of High Tc Superconductors, GaSr2Can-1CunO2n+3 (n=3; Tc=70 K, n=4; Tc=107 K) Prepared at High Pressure

Abstract
A new series of superconductors, GaSr2Ca n -1Cu n O2 n +3 ( n=3, 4), were prepared under a high pressure of 6 GPa at 1250°C. The n=4 member becomes superconducting below 107 K while the n=3 one below 70 K. From an analogy with the structure of the Ga-1212 phase, their X-ray patterns were indexed assuming orthorhombic lattices with the space group of I2 mb( Ima2, No. 46): a=5.454(1), b=5.391(1) and c=29.371(6) Å for the n=3 member and a=5.462(4), b=5.417(4) and c=35.78(5) Å for the n=4 one. They have structures closely related to those of Tl (or Hg)-1223 and 1234 phases.

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