The high pressure synthesis and characterization of some rare-earth based praseodymium-substituted R2Ba4Cu7O14+delta (R = Sm, Gd, Ho) cuprates

Abstract

The stability of phases in the (R1-xPrx)(2)Ba4Cu7O14+delta (R = Sm, Gd, Ho; Pr-doped R247) systems with x = 0 to 1.0 and with an increment of 0.1 in x was investigated. Samples of the title Pr-doped R247 phases were prepared at 980-990 degrees C under 20-36 bar of oxygen atmosphere, followed by long-time annealing at 300-320 degrees C under 110-115 bar of oxygen. Single-phased samples were obtained with substitution limit (x) equal to 0.5, 0.6 and 0.7 for phases of the title (R1-xPrx)(2)Ba4Cu7O14+delta series with R = Sm, Gd and Ho, respectively, as indicated by X-ray diffraction data. With increasing Pr content (x) both the lattice parameters and unit-cell volume were found to increase monotonically and, however, the corresponding crystallographic orthorhombicity, 2(b - a)/(b + a), was found to decrease with increasing x for all three Pr-doped series. The T-c of the Pr-doped R247 phases were found to be suppressed from 69, 70 and 92 K down to 20 K (x = 0.4), 18 K (x = 0.5) and 8 K (x = 0.7) for Pr-doped R247 phases with R = Sm, Gd and Ho, respectively. The composition coefficients of T-c, dT(c)/dx, were found to be -50.4, -48.5 and -55.5 K/Pr-atom per formula unit for the title Pr-doped R247 series with R = Sm, Gd and Ho, respectively. The crystal structure, temperature-dependent resistivity and magnetization data of the Pr-doped R247 phases synthesized in our study are described and their implications are discussed. (C) 1997 Elsevier Science B.V.