Ion size effect on Tc in (Pb,V)Sr2(Ca,R)Cu2Oz (R = Sm, Gd, Dy, Er and Lu) systems

초록

The superconducting transition temperature (T<inf>c</inf>) and lattice constants of (Pb,V)-based 1212 superconducting oxides (Pb<inf>1-x</inf>V<inf>x</inf>)Sr<inf>2</inf>(Ca<inf>1-y</inf>R<inf>y</inf>)Cu<inf>2</inf>O<inf>z</inf> (R = Sm, Gd, Dy, Er and Lu) which were prepared in an oxidizing atmosphere have been investigated. The as-prepared samples were annealed at 800 °C in oxygen and then quenched. The Pb:V ratio have been optimized for the highest T<inf>c</inf>. Correlation between the lattice constants and the ionic radii of R is observed in the compositions of (Pb<inf>0.6</inf>V<inf>0.4</inf>)Sr<inf>2</inf>(Ca<inf>1-y</inf>R<inf>y</inf>)Cu<inf>2</inf>O<inf>z</inf> with y = 0.35 and 0.40. The T<inf>c</inf> decreases with increasing R ion size as observed in (Pb,Cu)-1212 systems, which suggests that the R ion size dependence of T<inf>c</inf> can be a common characteristic of Pb-based 1212 systems. The sample with R = Lu and y = 0.35 exhibits T<inf>c</inf>(onset) = 70 K and T<inf>c</inf>(zero) = 63.8 K.