Figure 1. Resistive and magnetic properties of the samples after three typical thermal treatments.

(a) Temperature dependence of resistivity of the three typical samples SFC, S250 and S350 experiencing different thermal treatments. The SFC sample has a rather broad transition width and a large residual resistivity. (b) The resistive data shown in an enlarged view in low temperature region. In contrast, the sample S350 has a rather sharp superconducting transition at about 32 K with a small residual resistivity. (c) Temperature dependence of DC magnetization of the three samples measured with the zero-field-cooling (ZFC) and field-cooling (FC) modes at H=20 Oe. As the ZFC signal of the SFC sample is very small, it overlaps with the FC curves of the three samples.