【摘要】 用化学动力学探讨了Bi系超导相形成的机理,提出反应活化能是控制超导相形成的关键因素。在纯Bi系2223名义成份下,2212相的形成满足“晶核形成生长”自催化动力学模型,其动力学方程为α₂₂₁₂=1—exp(—k₂₂₁₂t^2.5)。2223相的形成较好地符合“收缩晶核界面”反应模型,动力学方程为1—(1—α₂₂₂₃)^1/3=k₂₂₂₃t。以0.35molPb替代Bi后,2212相形成的动力学规律没有本质改变,但是2223相的形成表现出区域反应的自催化效应,其相应的动力学方程为α₂₂₂₃=1—exp(—k_2223t。更多还原

【Abstract】 The mechanism for the formation of superconducting phases in Bi-based super-conductor was studied by chemical kinetics based on the results of X-ray analysis. In pure Bi-based superconductor, with nominal composition of Bi2Sr2Ca2Cu3O10, the formation of 2212 phase obeys the "nucleation and Crystalgrowth" self-catalytic reaction model: α2212 = 1-exp(-k2212t2.5); and the 2223 phase obeys the "nucleous shrinkage" model: 1 - (1 α2223)1/3=k2223t in this case, the activiation energy for the former is 60kJ·mol-1 higher than that of the latter, which makes the formation of 2223 phase more difficult. However, with 0.35 mol Pb doping into samples to substitute for Bi, the kinetic regularity for 2212 phase is still consistent with that in pure Bi-based superconductor, except that the activiation energy for the Pb-do-ped sample is lower than that of the Pb-free sample; to 2223 phase, the kinetic regu-larity is changed into α2223=1-exp(-k2223t) and its activiation energy is lowered about 100kJ·mol-1, which is close to that of 2212 phase. The investigation indica-ted that the transformation of 2212 to 2223 phase was not based on the diffusion of Cu-O plane and Ca-O plane into 2212 lattice but on chemical reraction.更多还原