Abstract: In comparison with the structure of hole-doped T phase (La_(2-x)Sr_x)CuO_4, electron-doped superconductors (Ln_(1.85)Ce_(0.15))CuO_(4-y), Ln=Pr, Nd, Sm, Eu, possess T phase structure with tetragonal I4/mmm symmetry. Their structural features are that the Cu ion is coordinated by four oxygen ions in square planar form and the Ln ion is located in octa-coordinate cubic site in the fluorite type LnO_2Ln duble layers. In this paper, the effects of preparation condition and cation substitution on the structure and superconductivity have been studied. Average ionic radius of Ln-site is limited in very narrow range. It can be changed by the substitution of larger or smaller ions. Its dimension is very important for structural type, structural stability under N_2 atmosphere and superconductivity.

Key words: Electron-doped Supereonductors, (Ln_1.85Ce_0.15)CuO_4-y, Ln=Pr,Nd,Sm,Eu,Structure, Superconductivity