High-Pressure Synthesis and Characterization of Rare-Earth Substituted (Y, R)2Ba4Cu7O15-δ (R = La, Tb, Yb, Lu) Cuprates

Teng-Ming Chen ； S. Y. Lee ； J. S. Ho

《Chinese Journal of Physics》 36卷2S期 (1998/04) Pp. 365-370

並列摘要

In an attempt to investigate the formation of unknown R2Ba4Cu7O15-δ (R247; R = La, Tb, Yb, Lu) phases, we have prepared and characterized four series of (Y1-xRx)2Ba4Cu7O15-δ(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,) were found to first increase and then decrease from 77.1 K of pristine Y247, whereas the width of superconducting transition (AT,) 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)2Ba4Cu7O15-δ(R = Y, Nd, Gd, Yb, Lu) phases were also synthesized and the effect of R3+ substitution on Tc was also investigated. With 10% of R3+ substitution Tc 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.