Dependence of superconducting properties on lattice strain in MgB2

As a phonon-media superconductor, the superconducting properties of MgB2 are very sensitive to the lattice parameters. Lattice strain has significant effects on the superconducting properties in MgB2 superconductor. We have systematically studied the relationship between lattice strain and superconducting properties (such as critical temperature, Tc, the upper critical field, Hc2, the irreversibility field, Hirr, and hence the critical current density, Jc) in pure and different chemical doped MgB2 samples. In contrast to the common practice of improving the Jc and Hc2 of MgB2 through chemical substitution, by taking advantage of residual thermal strains we are able to design a composite, which shows only a small drop in Tc and little increase in resistivity, but a significant improvement over the Jc and Hc2 of MgB2.