摘要
自1911年发现YBCO高温超导材料到现在,高温超导材料不仅临界温度Tc提高到160K,而且采用熔化工艺制备的Y系超导块材的临界电流密度Jc值提高到105A/cm2(77K,1T)。单畴YBCO超导块材以其具有较高的临界温度、临界电流密度、较大的磁悬浮力和稳定的物理性能而得到广泛的应用。本文主要研究了纳米Y2Ba4CuNbOx掺杂对单畴YBCO超导块材性能的影响和Nb2O5掺杂对单畴YBCO超导块材性能的影响。
通过顶部籽晶熔融织构工艺(TS-MTG)制备出不同Y2Ba4CuNbOx含量的纳米掺杂的单畴YBCO超导块材,同时对该类超导材料的宏观形貌、微观结构和磁悬浮力等性能进行了系统的分析,发现该系列样品的最佳掺杂是3.5wt%；其次制备了不同Nb205含量掺杂的YBCO超导块材,并对其系列样品的宏观形貌、微观结构和磁悬浮力等性能进行了分析,发现该系列样品的最佳掺杂是2.0wt%。
在制备掺杂纳米Y2Ba4CuNbOx的单畴YBCO超导块材之前,首先要制备Y2Ba4CuNbOx、YBa2Cu3Ox、Y2BaCuO5和Yb1.8Ba2.4Cu3.4Oy四种初始粉体,其制备方法均为固态反应法,采用四次球磨,三次烧结的步骤。四种初始粉体的烧结温度分别为1040℃,920℃,920℃和910℃,每次烧结时的保温时间均为24h。
掺杂纳米Y2Ba4CuNbOx对单畴YBCO超导块材性能的影响主要研究方面有：Y2Ba4CuNbOx初始粉体的晶体结构和晶格参数；以及不同含量Y2Ba4CuNbOx掺杂对单畴YBCO超导块材宏观形貌、显微结构、磁悬浮力的影响。通过XRD分析表明,Y2Ba4CuNbOx粉体的晶体结构是双钙钛矿结构,属于立方晶系,其晶格常数为8.437A；在掺杂不同Y2Ba4CuNbOx的单畴YBCO超导块材中,通过SEM图分析发现,Y2Ba4CuNbOx颗粒的尺寸大小普遍比Y2BaCuO5颗粒要小,且属于纳米材料。当掺杂量x=2.0wt%时,Y2Ba4CuNbOx粒子数最多,粒度也小；通过对此系列单畴YBCO超导样品的磁悬浮力的观察与测量发现,随着Y2Ba4CuNbOx掺杂量的增加,样品的磁悬浮力在增大,当掺杂量等于3.5wt%时,样品的磁悬浮力最大。进一步说明Y2Ba4CuNbOx的最佳掺杂是3.5wt%。
掺杂Nb2O5的单畴YBCO超导块材的影响主要研究方面有：不同含量Nb2O5掺杂对单畴YBCO超导块材的宏观形貌、显微结构和磁悬浮力的影响。通过SEM图分析发现,细小而且均匀的Y2BaCuO5分布在Y123基体上,其平均尺寸是0.81μm。当掺杂量x=2.0wt%时,Y2BaCuO5粒子数最多,粒度也较小;通过对此系列单畴YBCO超导样品磁悬浮力的观察与测量发现,随着Nb2O5掺杂量的增加,样品的磁悬浮力在增大,当掺杂量等于2.0wt%时,样品的磁悬浮力最大。进一步说明Nb2O5的最佳掺杂是2.0wt%。
Since 1911, YBCO high-temperature superconductor discovered, not only critical temperature of high-temperature superconductor is up to 160K, but also the critical current of Y-based material by preparation of melting process is up to 105A/cm2(77K, 1T). Single domain YBCO bulk superconductors are highly appreciated because of their higher critical temperature, critical current density, levitation force and physical stability. This paper mainly studied properties of the nanoparticles Y2Ba4CuNbOx doped the single-domain YBCO bulk superconductors and the Nb2O5 dopant the single-domain YBCO bulk superconductors.
YBCO bulk superconductors doped different Y2Ba4CuNbOx were prepared by top seeded melt texturing growth technique. Meanwhile, their macro-morphology, microstructure and levitation force were analyzed systematically. It is found optimum doping of Y2Ba4CuNbOx (3.5 wt%) in the series of samples.Secondly, we fabricated the single-domain YBCO bulk superconductors doped Nb2O5. Furthermore, their macro-morphology, microstructure and levitation force were analyzed. It is found optimum doping of Nb2O5 (2.0 wt%) in the series of samples.
Before fabricated the nanoparticles Y2Ba4CuNbOx doped single-domain YBCO bulk superconductors, the initial powders of Y2Ba4CuNbOx, YBa2Cu3Ox, Y2BaCuO5 and Yb1.8Ba2.4Cu3.4Oy were synthesized firstly. The above mentioned initial powders were sintered by solid state reaction methods using four ball mill and three sintering steps. The powders were sintered at temperature of 1040℃,920℃,920℃and 910℃for 24h.
During the preparation of the nanoparticles Y2Ba4CuNbOx doped single-domain YBCO bulk superconductors by the top seed melting texture growth method. Firstly, it is studied the phase structure and lattice parameters of the initial powders of Y2Ba4CuNbOx. Secondly, their macro-morphology, microstructure and levitation force of the nanoparticles Y2Ba4CuNbOx doped single-domain YBCO bulk superconductor were studied. The results of XRD showed that the crystal structure of Y2Ba4CuNbOx is cubic double pervoskite crystallographic structure with a unit cell size of 8.437A; It is found that the size of Y2Ba4CuNbOx is less than the size of Y2BaCuO5 in the nanoparticles Y2Ba4CuNbOx doped single-domain YBCO bulk superconductors and it belongs to nanomaterials. When the doping content of Y2Ba4CuNbOx (x=3.5wt%) the maximum number of Y2BaCuO5 particles, and particle size is also smaller.In the meantime, Furthermore, through observation and measurement of their levitation force of this series of single-domain YBCO sample with different Y2Ba4CuNbOx content. The levitation force was increasing gradually with the increasing of the Y2Ba4CuNbOx addition, the levitation force attained a largest value when x=3.5wt%. Further indicates that the best doped of Y2Ba4CuNbOx is 3.5wt%.
It is studied macro-morphology、microstructure and levitation force of the single-domain YBCO bulk superconductors with different Nb2Ox dopant. The SEM analysis shows that small and uniform distribution of Y2BaCuO5 particles in the YBCO matrix, their average size is 0.81μm. When the doping content of Nb2Ox(x=2.0wt%) the maximum number of Y2BaCuO5 particles, and particle size is also smaller. Furthermore, through observation and measurement of their levitation force of this series of single-domain YBCO sample with different Nb2Ox content. The levitation force was increasing gradually with the increasing of the Nb2Ox addition, the levitation force attained a largest value when x=2.0wt%. Further indicates that the best doped of Nb2Ox is 2.0wt%.
引文
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