RARE-EARTH SIZE-EFFECT ON T-C IN R(2-Z)CE(Z)CUO(4) HOMOLOGS

Because the defect responsible for doping R(2-z)Ce(z)CuO(4) is not iso lated rare-earth-site Ce but a (Ce, interstitial-oxygen) pair, the ons et of superconductivity in R(2-z)Ce(z)CuO(4), as a function of increas ing size of the trivalent rare-earth ion R, occurs when the lattice co nstants a and c become large enough to satisfy the approximate conditi on that (c(2) + 16a(2)) = 64[A(O-1) + A(O-2)](2), where A(O--Z) is the ionic radius of O--Z.