The effect of Er-substitution on the superconducting properties of MTG-YBaCuO crystals

The high quality Er-doping Y0.8Er0.2Ba2Cu3O7-δ (YErBCO) crystal is grown by the melted-textured-growth (MTG) method. The microstructure photograph shows that the MTG-YErBCO crystal has an obvious layered structure. Its magnetization loops show that the irreversibility field is decreased by Er-doping for H//c and that there is an anomalous behaviour, a second peak, in the magnetization curve for H//ab. The critical current density along the ab-plane (Jcab(77 K, 0 T)=4.75x104 A cm-2) is higher than that along the c-axis (Jcc(77 K, 0 T)=470 A cm-2). The field dependence of the irreversibility temperature Tirr follows a power law, H=H0(1-Tirr(H)/Tirr(0))1.3, with H0=550 T for H//ab and 51 T for H//c, respectively. The field dependence of the activation energy Ue shows a different behaviour for H//ab and for H//c, namely a linear relation, U=49131-3006H, for H//ab and a power law, U∝H-0.68, for H//c, respectively. The anisotropy factorγ=15 was obtained from the angular dependences of the activation energy and the irreversibility temperature. A possible reason for the effect of Er addition on the flux-pinning behaviour has been discussed. (author)