THE HIGH-PRESSURE SYNTHESIS AND CHARACTERIZATION OF SOME PRASEODYMIUM-SUBSTITUTED RARE-EARTH-BASED R2BA4CU7O14+DELTA (R = ND, EU, TM)

摘要

The formation of phases in the (R1-xPrx)(2)Ba4Cu7O14+delta (Pr-doped R247; R = Nd, Eu, Tm) system with x = 0-1.0 was investigated. Samples of the title series were synthesized at 980-990 degrees C at 25 bar O-2, followed by annealing at 300 degrees C under 130 bar O-2 for 30 hr. Oxygen content of the samples has been determined by iodometric titration, Single-phased samples were obtained with x smaller than or equal to 0.3, 0.4, and 0.4 for R = Nd, Eu, and Tm, respectively, as indicated by X-ray diffraction measurements, With increasing amount of Pr substituting for R, the cell dimensions of the Pr-doped R247 phases were found to expand steadily, whereas the corresponding structural orthorhombicity was observed to decrease systematically. Superconducting transition temperatures (T-c's) of the title phases were found to be significantly suppressed upon Pr doping, as indicated by field-cooled temperature-dependent magnetization studies. The effect of Pr substitution on T-c's of R247 (R = Y, Eu, Er, Tm, Nd, Dy) phases was investigated and compared as a function of R3+ radii, but no size dependence effect was observed. In addition, field-dependent magnetization studies for a series of (Eu1-xPrx)(2)Ba4Cu7O14+delta samples with x = 0, 0.2, and 0.4, respectively, are also reported. (C) 1997 Academic Press. [References: 20]