Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：

SUPERCONDUCTIVITY IN Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe, Ni) SYSTEMS

The relation of crystal structure, oxygen content, normal state resistivity with. temperature and superconducting critical temperature of Y_1-xCa_xBa₂Cu_3-xM_xO_7-δ(M = Fe, Ni) systems have been studied. In comparison with YBa₂Cu_3-xM_xO_7-δ (M = Fe,Ni) systems, it is found that the superconducting T_c of Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ system is remarkably higher than that of YBa₂Cu_3-xFe_xO_7-δ system with the same x value. On the contrary, the T_c of Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ system is lower than that of YBa₂Cu_3-xNi_xO_7-δ system. These results show that the variation of the carrier concentration (n_H) due to Ca and Fe substitutions has been compensated and the sharp decreases of n_H and T_c are prevented when Ca and Fe simultaneously substitute for Y and Cu(I). But in the case of Ca and Ni simultaneous substitutions, the compensation of the carrier concentration is not important and the correlation of Ca and Ni substitutional effects is weak. We suggest that the carrier concentration is an essential factor to determine T_c when the element substitution occurs out of the CuO planes, such as in Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ system, but the pair-breaking effect is more important when Ni²⁺ ions substitute mainly into Cu(II) sites in Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ system and T_c is directly suppressed by the pair-breaking effect.