High-pressure synthesis and characterization of rare-earth substituted (Y,R)(2)Ba4Cu7O15-delta (R = La, Tb, Yb, Lu) cuprates

Abstract

In an attempt to investigate the formation of unknown R2Ba4Cu7O15-delta (R247; R = La, Tb, Yb, Lu) phases, we have prepared and characterized four series of (Y1-xRx)(2)Ba4Cu7O15-delta (R-doped Y247; R = La, Tb, Yb, Lu) cuprates. The substitution limit of R for Y was determined to be <: 10%, 50%, < 20% and 30% for phases with R = La, Yb, Tb and Lu, respectively, as indicated by x-ray diffraction (XRD) patterns. The lattice parameters for R-doped Y247 (R = Yb, Lu) phases were found to decrease with increasing R content due to the smaller size of R3+ compared to that of Y3+. With increasing content of R's the superconducting transition temperature (T-c) were found to first increase and then decrease from 77.1 K of pristine Y247, whereas the width of superconducting transition (Delta T-c) was found to increase with increasing dopant R content. The oxygen contents of R-doped Y247 phases have been experimentally determined by iodometric titration and were found to vary in a small range. Furthermore, a series of (Y0.9R0.1)(2)Ba4Cu7O15-delta (R = Y, Nd, Gd, Yb, Lu) phases were also synthesized and the effect of R3+ substitution on T-c was also investigated. With 10% of R3+ substitution T-c of R-doped Y247 phases was discovered to decrease with increasing ionic radii of R3+ and the corresponding oxygen composition was found to be essentially unchanged.