New series of oxyphosphate superconductors (Cu0.5P0.5)Sr-2(Ca,Y)(n-1)CunOy((Cu,P)-12(n-1)n, n=3-6) prepared under high pressure

New series of cuprate superconductors containing phosphate groups, (Cu0.5P0.5)Sr-2(Ca,Y)(n-1)CunOy (n = 3-6), were newly synthesized under high pressure of 5-6 GPa. They show superconductivity with various T-c of 80-64 K for n = 3, 112-70 K for n = 4 and similar to 80 K for n = 5, 6, depending on yttrium and oxygen contents. Electron diffraction and HRTEM observations revealed that compounds of this series have M-12 (n-1)n (e.g. Tl-12(n-1)n) type structures with Cu-P mixed atoms at the M sites, The copper and phosphorus atoms of each phase are placed in an ordered way within the (Cu,P) plane forming a superstructure of 2a x b x 2c with respect to a basic tetragonal lattice, a, b, c.