Preparation and properties of superconducting Y(Ba1−xSrx)2Cu4O8

Abstract

We have prepared single-phase or near-single-phase Y(${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${)}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ (0≤x≤0.4) samples by means of a high-oxygen-pressure technique using an ${\mathrm{O}}_2$ hot isostatic pressing. All the lattice constants, a, b, and c, of Y(${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${)}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ monotonically decreased with increasing Sr content. The superconducting transition temperatures of these samples were nearly constant, being around 80 K, while the ${\mathit{T}}_{\mathit{c}}$’s of Y(${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${)}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{z}}$ (z∼7) samples decreased with increasing Sr content. When Y in Y(${\mathrm{Ba}}_{0.8}$ ${\mathrm{Sr}}_{0.2}$ ${)}_2$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_8$ was partially substituted by Ca, the superconducting critical temperature increased to near 90 K.