Doping of Nb to the Ba and Cu sites in the Y 0.6 Gd 0.4 Ba 2 Cu 3 O 7-δ

Polycrystalline samples of Y 0.6 Gd 0.4 Ba 2-x Nb x Cu 3 O 7-δ and Y 0.6 Gd 0.4 Ba 2 Cu 3-x Nb x O 7-δ with different Nb contents (x=0.025, 0.075, 0.125, 0.175 and 0.225) were prepared using the solid state reaction method. Structural and electrical properties of new compounds were investigated with optical microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD), Four Point Probe (FPP). The results indicated that Nb constituted YBa 2 NbO 6 structure instead of substituting to the Y 0.6 Gd 0.4 Ba 2 Cu 3 O 7-δ structure. YBa 2 NbO 6 structures gathered between grains. Transition temperature did not change significantly, but critical current (J c ) values decreased with increase of Nb concentration. The underlying reason is that the oxygen concentration of compounds remained unchanged due to Gd; thus, T c values did not change significantly. © 2012 Springer Science+Business Media New York.