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

Abstract A series of single-phase RBa 1.5 Sr 0.5 Cu 3 O y (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 RBa 1.5 Sr 0.5 Cu 3 O y 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 (t p ), the amount of oxygen loss (Δw) in this transition, and the enthalpy of fusion (ΔH f ), respectively. An increase in the ΔH f is correlated with increasing t p for the respective orthorhombic and tetragonal phases of RBa 1.5 Sr 0.5 Cu 3 O y compounds. T c of the title compounds gradually increased from 52 to 86 K with a decrease in the radius of the R ion.