Preparation, structure, and peritectic transition of RBa1.5Sr0.5Cu3Oy (R = La, Nd, Sm, Eu, Gd, Dy, Ho, and Y) superconductors

A series of single-phase RBa1.5Sr0.5Cu3Oy (R = La, Nd, Sm, Eu, Gd, Dy, Ho, and Y) compounds with a triple-perovskite unit cell has been prepared by solid-state reaction method. Samples with a larger radius of the R ion (R = La and Nd) are tetragonal, whereas those with a smaller radius of the R ion (R = Sm, Eu, Gd, Dy, Ho, and Y) are orthorhombic. Unit-cell parameters of RBa1.5Sr0.5Cu3Oy decrease monotonically with a decrease of the radius of the R ion. A maximum at R = Nd, Sm, and Eu is found in the peritectic transition temperature (tp), the amount of oxygen loss (Δw) in this transition, and the enthalpy of fusion (ΔHf), respectively. An increase in the ΔHf is correlated with increasing tp for the respective orthorhombic and tetragonal phases of RBa1.5Sr0.5Cu3Oy compounds. Tc of the title compounds gradually increased from 52 to 86 K with a decrease in the radius of the R ion.