Neutron diffraction study of the layered cuprate Sr 2−xNd 1+xCu 2O 6−y

Abstract

New layered cuprates Sr 2− x Nd 1+ x Cu 2O 6− y , Sr 2− x A x NdCu 2O 6− y (A=Ca, Ba) and Sr 2Nd 1− x La x Cu 2O 6− y have been synthesized and characterized by X-ray and electron diffraction. The structure of the extreme phase Sr 2NdCu 2O 5.76 has been deteined by neutron diffraction. This oxide is a [2, 1]-member of the (ACuO 3− x ) m (A′O) n series of layered cuprates, i.e. corresponds to an intergrowth of single rock salt-type layers with double oxygen-deficient perovskite layers. However, the ordering of oxygen vacancies in the perovskite slabs is very complex and different from that observed in the classical [2, 1]-member La 2CaCu 2O 6. The structure can be described by two extreme models (I) and (II). The first model which involves only CuO 5 pyramids in the perovskite slabs is also characterized by hexagonal tunnels, whereas the second one which involves CuO 4 groups and CuO 5 pyramids (II) can be described as an intergrowth of “123”-slabs with single rock salt layers. Although they exhibit a mixed valency Cu(II)-Cu(III), these oxides do not superconduct.