Superstructures in novel Sr‒Ca‒Cu‒Au‒O phases synthesized under high pressure

Abstract Novel compounds having the formulae (Au x Cu 1‒ x )Sr 2 CaCu 2 O y ((Au,Cu)‐1 (Sr) 212) and Sr 2 Ca 2 (Au,Cu) 3 O y (0 (Sr) 223) and exhibiting superstructures were synthesized at 5.5 GPa and 1100°C‒1150°C. The structures of these materials were assessed using X‐ray diffraction and field emission transmission electron microscopy. The sub‐structures of the resulting (Au,Cu)‐1 (Sr) 212 and 0 (Sr) 223 phases were found to have the lattice parameters a ≈ 3.86 Å and c ≈ 10.98 Å and a ≈ 3.88 Å and c ≈ 27.21 Å, respectively. Analyses by X‐ray photoelectron spectroscopy indicated that the Au in these compounds was primarily in the Au 3+ state. (Au,Cu)‐1 (Sr) 212 specimens with Au/Cu ratios ≥0.3 and 0 (Sr) 223 specimens with Au/Cu ratios ≥0.25 exhibited superstructures. The ordered arrangements of Au and Cu in the charge reservoir layers and the CuO 2 planes likely generated these superstructures.