Role of silver addition in the synthesis of high critical current density MgB_2 bulk superconductors

摘要

Ag-doped MgB_2 bulk superconductors have been prepared using a standard solid state processing. The addition of Ag to MgB_2 powders during the sintering process has been found to result in an important advantage, namely, the prevention/reduction of Toss of Mg, a problem most commonly observed in the sintering of MgB_2 bulk samples at elevated temperature and ambient pressures. The Ag-doped MgB_2 sample has a distinct superconducting transition temperature around 39 K, while the undoped MgB_2 undergoes only a very feeble transition to a diamagnetic superconducting state at around 39 K. The normal conducting silver regions in the MgB_2 matrix act as pinning centres resulting in the realization of high critical currents in the presence of magnetic fields.