A NEW HOMOLOGOUS SERIES SRN-1CUN+1O2N FOUND IN THE SRO-CUO SYSTEM TREATED UNDER HIGH-PRESSURE

A new homologous series of high-pressure phases, Srn-1Cun+1O2n (n = 3, 5, ...), were found in the SrOCuO system treated at 6 GPa and 1373-1573 K. These crystallize in orthorhombic structures of space group Cmmm with unit-cell parameters of a ∼ 3.9 Å, b ∼ n × a, and c ∼ 3.5 Å. Along the c-axis Cu1+ 1 nO2 sheets alternate with Sr1- 1 n sheets without oxygen. Within the CuO sheets, CuO double chains made of corner- and edge-sharing CuO4 squares are intergrown with a corner-sharing CuO4 network; the distance between the double chains is b 2. The serial chemical composition and structure are interpreted as resulting from a shear operation upon the high-pressure form of SrCuO2 (n = ∞). © 1991.