Structure analysis of superconducting Au-1212 cuprate

Single crystals of Au0.82Ba2Y0.77Ca0.23Cu2.18C6.85 (Au-1212) have been grown for the first time at 6 GPa and 1380DGC. This phase is the second member of the Au-containing cuprate family of AuBa2(Y,Ca)n-1CunO2n+3 and it exhibited bulk superconductivity with Tc = 84 K. The crystal structure of the Au-1212 phase was determined from single-crystal x-ray data (space group Pmmm, a = 3.8260(2) A, b = 3.8501(2) A, c = 12.075(1) A, R(I > 3*s(I)) = 0.0260, Rw(I > 3*s(I)) = 0.0219). No superstructure was revealed. The main feature of the Au-1212 crystal structure is the partial substitution of Cu1+ for Au, and this results in oxygen vacancies in this plane. Surprisingly, AuO4 planar units form a zigzag chain along the short *a-axis.