The role of starch doping on the superconducting properties of MgB2

• First report on effect of starch addition on superconducting properties of MgB2.
• Jc Enhances by ∼42 times at 20 K (4 T) for starch (2 wt.%) added MgB2.
• Unlike C doped MgB2, Jc enhances both at low and high fields for starch added MgB2.
• Field dependence of Jc is well explained by collective pinning model.
• Critical current density exhibits excellent scaling.

The effect of different amount of starch addition on structural and superconducting properties of superconducting MgB2 has been discussed. The samples are synthesized by conventional solid reaction method. XRD analysis confirms that carbon, which is produced during synthesis due to decomposition of starch, is substituted in the B sites. High resolution transmission electron microscope (HRTEM) picture infers the presence of large number of nanosized precipitates (size ∼10–20 nm) in starch doped MgB2 pellets. Superconducting transition temperature (Tc0) of MgB2 (∼38 K) decreases due to the addition of starch. The critical current density (Jc) of starch added MgB2 samples, however, shows significant improvement in whole field range, especially at high magnetic fields. MgB2 added with 2 wt.% of starch gives the best performance amongst the investigated samples and at 20 K displays ∼42 times enhancement in Jc under 4 T field compared to that for pure MgB2. The field dependence of the critical current density (Jc) of starch added MgB2 is explained fairly well in terms of collective pinning theory. An excellent scaling of the reduced critical current density, Jn(=Jc/Jc(0)) and the reduced field hn (=H/H0) is observed for both pure and starch added MgB2 polycrystalline pellets at different temperatures, where Jc(0) and H0 are the fitting parameters obtained from collective pinning model. However, the normalized pinning force density (FP/Fp(max)) of starch added samples does not display any scaling, but shows an excellent correspondence with modified Dew–Hughes expression. The presence of anisotropy and grain orientation is thought to be responsible for the absence of scaling of normalized pinning force density in starch added MgB2 pellets.