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

铅基氧化物超导体同系物性能研究

基本信息

批准号：
06650001
负责人：
NOJI Takashi
金额：
$ 1.41万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

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.

研究了Pb基铜酸盐Pb_2Sr_2A_Cu<n-1>_（n+1）O_（2n+4+ δ）（A：稀土元素和碱土金属），即Pb_（32）（n-1）n相.研究了氧对聚合络合法制备的Pb-3201相多晶样品的影响。研究发现，额外的氧为CuO_2片层提供了空穴载流子.用<1-x>助熔剂法生长了Pb-3212相（0 × 0.5）的Pb_2Sr_2Y_Ca_xCu_3O_8单晶。发现各向异性参数γ =（m_c^<**>/m_<ab>^<**>）^<1/2>随着x的减小而增大，即随着空穴浓度的减小而增大。通过<irr>对这些单晶的磁化强度测量，研究了不可逆场H_和磁化曲线中的反常第二峰。在T_c '附近的高温区，不仅H_p<irr>，而且在每个降低的温度t=T/T_c处的第二峰值场H_p都大致与γ_p成比例<-2>。对于γ值较大的晶体，<irr>低温区强磁场中的H_是由于二维涡旋-晶格熔化.我们尝试用改进的聚合络合法制备Pb-3223相的块状样品。然而，尽管做了很多努力，Pb-3223相还没有产生。当烧结温度高于700 ℃时，生成Pb-3212相，而低于700 ℃时生成Ca_2PbO_4相。