Synthesis and characterization of Pr0.9Ca0.1Ba2Cu4O8 by an aqueous solution method

The synthesis of the Pr1−xCaxBa2Cu4O8 system with x=0, 0.1 was achieved by the amorphous citrate method, without using high oxygen pressure or special additives. A 1-atm oxygen pressure and two thermal treatments of 60 h at 850°C were sufficient for the effective preparation of 124 phase with very low impurities content in the PrBa2Cu4O8 system. With introducing Ca into the Pr site, the effective incorporation of Ca2+ into the orthorhombic structure of 124 system was found to produce interesting modifications: the decrease in the lattice parameters and the unit volume cell and the disappearance of the peaks characteristic of lower symmetry. X-ray diffraction (XRD) patterns demonstrated that in the Ca-substituted 124 phase, a cationic disorder is induced in the lattice. Room temperature Raman spectra for Pr(Ca)124 have shown that the characteristic peaks of the 124 phase were present, but the registered bands were wider, an effect that can be attributed to the disorder introduced by the presence of Ca. Both materials showed similar thermal stability. The magnetic susceptibilities were determined using SQUID measurements and showed similar behaviour; no superconductivity was observed down to 5 K.