NEW COMPOUND SR3CA3CU6O12+ -DELTA WITH MODULATED SUPERSTRUCTURE/

A new ordered phase with a composition close to Sr3Ca3Cu6O12+delta has been found in a specimen, prepared by a high-pressure technique, whic h showed superconductivity. It was found from selected-area diffractio n (SAED) and high-resolution transmission electron microscopy (HRTEM) studies that this phase has a wavy modulated superstructure, with latt ice parameters alpha congruent to alpha(c), b approximate to 6 alpha(c ) and c approximate to 6 alpha(c), where alpha(c) is the cubic perovsk ite parameter. A tentative structural model based on the two-dimension al ordering of Sr and Ca atoms in the SrCuO2 infinite-layer (IL) basic structure is proposed.