ELECTRON-DOPED SYSTEM (LA, ND, CE)2CUO4 AND PREPARATION OF T'-TYPE (LA, LN)CUO4 (LN=CE, Y)

Superconductivity of the electron-doped system LaxNd1.85-xCe0.15CuO4-y was studied. The solid solution has a T′-type structure and ranges up to x=1.1. Tc of the system depends not only on the La-content x but also on the oxygen deficiency y. The dependence of Tc on y was obtained for the sample with x=0.8 and compared with the previous results for the sample with x=0. In both compounds, oxygen deficiency is indispensable to realize superconductivity but a very small level of deficiency is enough and more defects suppress Tc. It was found that T′-type (La, Ln)2CuO4 (La=Ce and Y) can be prepared at lower temperatures (∼600°C) using a coprecipitation technique, while they cannot be obtained at higher temperatures by the usual solid-state reaction. They did not show superconductivity even after reduction. © 1990.