Rare-earth ionic size effects on T c in the series RBa 2Cu 3O 7-σ

Abstract

The rare-earth ionic size effects on T c are investigated in terms of bond valence sums using the neutron diffraction data for nearly optimal doped RBa 2Cu 3O 7-σ (R Y, La, Nd, Sm, Dy, Ho, Er, Tm, and Yd) and PrBa 2Cu 3O 7-σ systems. The optimal hole concentration in CuO 2 planes is found to decrease systematically with increasing rare-earth ionic radius except Pr-123 in the R-123 phases, which is confirmed by the two similar inverted parabolic curves of T c vs hole concentration for Y-123 and Er-123. The anomalous property of Pr-123 is due to the depletion of hole concentration. The increase in T c as R 3+ ionic radius is interpreted as both the increase of hole distribution on the in-plane O sites relative to the in-plane Cu sites and the interplanar coupling.