Abstract
With an attempt to increase the Cu valence, we synthesized the (La1-xSrx)(8)Cu8O20-delta (8-8-20 phase) compounds with large x using an O-2-HIP apparatus. By heat treatment in a high-pressure of oxygen gas (40 MPa), the 8-8-20 compounds were stabilized in the range of 0.25 less than or equal to x less than or equal to 0.65. Their crystal structures, characterized by x-ray Rietveld refinement and electron diffraction, are tetragonal, space group P4/mbm. The formal copper valence was found to increase with Sr concentration from 2.24 at x = 0.25 to 2.63 at x = 0.65, keeping the oxygen content constant around 20.0. Electrical resistivity and magnetic susceptibility showed only metallic behavior from room temperature down to 5 K with no sign of superconductivity.