Studies of properties in the homologous series of Pb-based oxide superconductors

我们研究了Pb_2Sr_2A_<n-1>Cu_<n+1>O_<2n+4+ δ > （A：稀土元素和碱土），即Pb32 (n-1) n相。我们研究了额外的氧对聚合络合物法制备的Pb-3201相多晶样品的影响。结果表明，多余的氧为CuO_2片提供了空穴载流子。用通量法生长出了Pb_2Sr_2Y_<1-x>Ca_xCu_3O_8的Pb-3212相单晶，尺寸为0*x*0.5。各向异性参数γ =(m_c^<**>/m_<ab>^<**>)^<1/2>随x的减小而增大，即随空穴浓度的减小而增大。通过对这些单晶的磁化测量，研究了磁化曲线上的不可逆性场H_<irr>和反常第二峰。在T_<c'>附近的高温区，不仅H_<irr>，而且在每个还原温度t= t /T_c下的第二峰场H_p与γ ^<-2>大致成正比。对于gamma值较大的晶体，H_<irr>在低温状态下的高磁场作用是由于二维涡晶格熔化造成的。我们尝试用改进的聚合配合物方法制备Pb-3223相的散装样品。然而，尽管付出了很多努力，Pb-3223阶段仍未生产出来。在700ºC以上的烧结温度下，生成Pb-3212相，在700ºC以下生成Ca_2PbO_4相。

We have investigated Pb-based cuprates Pb_2Sr_2A_<n-1>Cu_<n+1>O_<2n+4+delta> (A : rare earth elements and alkaline earths), so-called Pb32 (n-1) n phases.1. We have investigated the effects of extra oxygen for polycrystalline samples of the Pb-3201 phase, prepared by the polymerized complex method. It has been found that the extra oxygen supplies the CuO_2 sheets with hole carriers.2. We have grown Pb_2Sr_2Y_<1-x>Ca_xCu_3O_8 single crystals of the Pb-3212 phase with 0*x*0.5 by means of the flux method. The anisotropic parameter gamma=(m_c^<**>/m_<ab>^<**>)^<1/2> has been found to increase with decreasing x, namely, with decreasing hole concentration. The irreversibility field H_<irr> and the anomalous second peak in the magnetization curves have been studied from the magnetization measurements for these single crystals. In the high temperature regime near T_<c'> not only H_<irr> but also the second peak field H_p at each reduced temperature t=T/T_c are roughly proportional to gamma^<-2>. For crystals of larger gamma values, H_<irr> in high magnetic fields in the low temperature regime is due to two-dimensional vortex-lattice melting.3. We have tried to prepare a bulk sample of the Pb-3223 phase by the modified polymerized complex method. However, the Pb-3223 phase has not been produced in spite of a lot of efforts. At sintering temperature above 700ﾟC,the Pb-3212 phase is produced, while Ca_2PbO_4 is produced below 700ﾟC.