Controlling flux pinning precipitates during MgB2 synthesis

MgB2 samples prepared by three different sets of synthesis parameters were investigated using transmission electron microscopy. Results suggest that oxygen dissolved in bulk MgB2 at high synthesis temperatures when the MgB2 samples were exposed to trace amount of oxygen from flowing ultrahigh purity Ar gas. The lower solubility of oxygen in MgB2 at a lower temperature led to the precipitation of nanometer-sized coherent Mg(B,O) in the interior of MgB2 grains during subsequent cooling. The precipitates, which act as effective flux pinning centers, are of composition-modulated structures with the same basic crystal lattice and orientation as the MgB2 matrix. This study has demonstrated the potential of tailoring the size and distribution of Mg(B,O) precipitates through optimizing synthesis parameters for optimum flux pinning. (C) 2002 American Institute of Physics.