A significant improvement of the critical current properties in MgB2 bulk was attained by sodium carbonate doping. A series of Mg1-2xB2(Na2CO3)x bulk samples with x = 0 to 0.1 were prepared by solid-state reaction in sealed stainless tubes. Both the critical current density, JC, and irreversibility field, Hirr, at 20K were systematically improved up to x = 0.055 and decreased monotonically by excess doping, while their TC values were continuously decreased with increasing x. The sample with x = 0.055, having a slightly decreased TC of 37.6K, recorded the best critical current performance at 20K with a JC of 3.8 x 105A/cm2 in self-field and μ0Hirr of approximately 6T. Both small particles of MgO and a C-containing local region, Mg(B,C)2, were believed to act as effective pinning centers, resulting in an enhancement of the flux pinning force. In addition, the coherence length ξ of the MgB2 was dramatically shortened by sodium carbonate doping, and consequently the μ0HC 2 was enhanced to approximately 29T at the highest doping level of x = 0.10.

Enhanced Critical Current Properties Observed in Na2CO3-Doped MgB2. S.Ueda, J.Shimoyama, A.Yamamoto, S.Horii, K.Kishio: Superconductor Science and Technology, 2004, 17, 926-30