Stress/strain induced flux pinning in highly dense MgB2 bulks

We have systematically studied the flux pinning behavior of MgB2 bulks synthesized by direct diffusion of Mg into pressed pellets of high purity crystalline B powder, with and without mixing with C and SiC nanoparticles, at a reaction temperature of 850° C for 10 hrs. All of the samples showed very high purity and high density, but their microstructure and flux pinning behavior showed significant differences. It was found that the pure MgB2 agrees with the δTC pinning model, nano-C doped MgB2 agrees with the δI pinning model, while the SiC + MgB2 composite agrees with the δ ε pinning model (stress/strain field pinning), since the dominant micro-defects that influence the flux pinning in these three samples are different.