【摘要】 利用固相反应法制备了非化学计量的二元金属硼化物超导体Mg1 +xB2 (x=0 ,0 .1 ,0 .2 ) .粉末X光衍射 (XRD)表明较多的过量Mg极易导致绝缘的MgB6和MgO杂相 ,Mg与MgB2 不易形成固溶体 .当杂相较少时 ,对样品电阻率和交流磁化率研究发现其超导临界温度Tc 几乎不受杂相的影响 ,但正常态电阻率随Mg过量增加而迅速增大 ,同时抗磁屏蔽信号下降 .对交流磁化率的实部、虚部与Mg含量等关系作了讨论 .我们的结果说明过量Mg导致的杂质对晶界区的Josephson耦合有破坏作用 .更多还原

【Abstract】 Nonstoichiometric binary metal diboride superconductors Mg-{1x}B-2 (x0, 0.1,{0.2}) were prepared by solid state reaction method. The powder X-ray diffraction patterns indicate that the excess amount of Mg lead easily to the insulating MgB-6 and MgO impurities and the solubility of Mg in MgB-2 is limited. When the impurity density is not very high, the superconducting transition temperature T-c is hardly affected from the study of its resistivity and a.c. susceptibility, but the resistivity in normal state increases rapidly and the diamagnetic screening signal deceases fast with increasing x. The relation between the real and imaginary part of a.c. susceptibility and the excess amount of Mg is discussed. Our result show that the insulating impurities caused by excess amount of Mg will impair the Josephson coupling in the grain boundaries.更多还原