摘要
Samples of Bi_(2.2)Sr_(1.8)Ca_(1.05)Cu_(2.15-x)Na_(x)O_(8+y)(x=0,0.7)were prepared by melt-processing technique.The maximum transition temperature increased up to 100 K,and T_(c)0 achieved 92.5K.In order to study the mechanism of T_(c) increasing,samples were annealed in a flowing oxygen,atmosphere.The reversibility of T_(c) was observed in undoped sample,while the T_(c) of Na-doped sample had no significant changes.We believe that the T_(c) is correlated with a redistribution of holes between the BiO layers and the CuO planes.Doping sodium changes the hole density of CuO planes into an“optimium”value so as to increase T_(c).
基金
the National Center for Research and Development on Superconductivity
the National Doctoral Education and Center of Material Analysis of Nanjing University.
