Ba Gd Research Articles

Phase evolution in Ba–(Nd,Eu,Gd)–Cu–O-coated conductor films

Phases that are in equilibrium with BaR2CuO6+x (R=lanthanides and Y), such as the “green-phase” and “brown-phase” structural variants of BaR2CuO5 in bulk samples, are attractive choices for flux-pinning for coated conductor applications because of the guaranteed chemical stability. In films, high-temperature x-ray diffraction studies of Ba2RCu3O6+x superconductor deposited on SrTiO3 substrate using the trifluoroacetate solution method demonstrate that while BaNd2CuO5 (“brown-phase” structure) develops at 735 °C and 100 Pa pO2, neither BaGd2CuO5 nor Ba(Nd1/3Eu1/3Gd1/3)2CuO5 (both green-phase structure) form at these conditions. As a result, Ba2(Nd1/3Eu1/3Gd1/3)Cu3O6+x in thin films is in equilibrium with the brown-phase, and Ba2GdCu3O6+x is in equilibrium with Gd2O3 in the Ba–Gd–Cu–O system, in contrast to the bulk systems. Different phase relationships in the vicinity of the Ba2RCu3O6+x phase imply different phases are available for flux-pinning applications. These differences will need to be considered carefully in designing optimized superconducting coated conductors.

Evidence of new layered cuprates in the Hg–A–Gd–Cu–O system (A = Ba, Sr)

Syntheses, structures, electrical and magnetic properties Hg1 –xGdxA2GdCu2O7 –δ(A = Ba, Sr) and Hg2 –xGdxBa2GdCu2O8 –δ layered cuprates have been reported. These compounds crystallize in tetragonal 1212- and 2212-type structures, respectively. They are prepared under normal oxygen pressure and are semiconductors. Magnetic susceptibility measurements reveal antiferromagnetic ordering of Gd magnetic moments in both 1212 and 2212 compounds in a narrow temperature range (Tn= 2.25–2.4 K). Electron microscopy studies of the Hg–Ba–Gd–Cu–O system prepared under an oxygen pressure of a few bars evidenced intergrowths between the 1212 and 123 structures.