Absence of Solid Solution of the Type, Y(Ba_2-xRE_x)Cu₃O_7±δand Its Possible Implications

The results of X-ray diffraction and resistivity measurements of the specimens Y(Ba 2- x RE x )Cu 3 O 7±δ (RE=Ce, Pr, Eu and Gd; x \lesssim0.4) are presented. The results suggest that the RE ions are not soluble with Ba in this series. This indicates that RE-Ba ionic size differences alone cannot explain the solubility behaviour normally observed in REBa 2 Cu 3 O 7±δ compounds. We propose that O-O repulsive interaction plays a major role in deciding the solubility limits.