单畴GdBCO超导块材生长过程中微纳尺度Gd211粒子网状显微组织结构的演化机制与性能

RE211 particle additions is the most practical and effective method to introduce flux pinning centers in REBCO bulk superconductor, a smaller RE211 particle is of stronger flux pinning force. But the larger size of RE211 particle, serious macro segregation of RE211 particle and higher porosity is the key problems in REBCO bulks fabricated by traditional melt growth process. This project will study the evolutionary mechanism and properties of Micro- and nano-scale Gd2BaCuO5 (Gd211) particle networks during the fabrication of single domain GdBCO bulk superconductor by Top seeded infiltration and growth process (TSIG) with a new solid phases (Gd2O3 +xBaCuO2). The phase compositions and microstructure of the new solid phases sintered at different temperature will be investigated to identify the evolutionary mechanism of the microstructure networks of the new solid phases before and after Gd211 particle formed. The effect of the new solid phases on the Gd211 particle and porosity distribution, and the GdBCO crystal growth dynamics will be investigated to illustrate the formation mechanism of the new nano-scale particles, the evolutionary mechanism of the Gd211 particle and porosity distribution in GdBCO bulk superconductor, and the GdBCO crystal growth mechanism by using the new solid phases. The effect of the new solid phases on the critical current dengsity Jc, levitation force and trapped field etc. of the GdBCO bulk superconductors will be investigated to elucidate the flux pinning mechanism of the new nano-scale particles and the Gd211 particles. Finally, a new and high efficiency method for introducing the new nano-scale particles, improving the unmiformity of Gd211 particles distribution and lowering the porosity in GdBCO bulk superconductor will be established, which provides a new idea for fabrication of high quality of GdBCO bulk superconductor.

RE211粒子掺杂是提高REBCO超导块材磁通钉扎能力的有效方法，且粒度越小磁通钉扎力越强；但传统方法制备的样品存在RE211粒子尺度大、偏析严重和气孔率高的问题。本研究将以(Gd2O3 +xBaCuO2)为新固相源，采用顶部籽晶熔渗生长法制备单畴GdBCO超导块材。研究新固相源的物相和显微组织变化规律，阐明Gd211粒子从无到有、及其长大过程中网状显微组织结构的形成及演化机制。研究新固相源对GdBCO块材中Gd211粒子和气孔分布、及晶体生长的影响规律，阐明新生纳米粒子的生成机制、揭示Gd211粒子分布和气孔形成的演化机理、阐明新固相源对单畴GdBCO块材生长规律的影响机制。研究制备样品的Jc、磁悬浮力和捕获磁通等，阐明新生纳米粒子和Gd211粒子的磁通钉扎机制。创建一种能够高效引入新生纳米粒子、提高RE211粒子均匀性和降低气孔率的新方法，为制备高质量单畴REBCO超导块材提供新思路。

采用我们发明的RE+011 TSIG法研究了提高单畴GdBCO块材超导性能的方法和机制。通过对不同温度烧结新固相源坯块显微结构分析发现，随着温度的升高，其中的Gd211粒子从无到有、从小长大并逐渐演化成了Gd211粒子相互连接的网状显微组织结构；温度越高，Gd211粒子越大，粒子间隙越小；最佳超导性能对应的并非Gd211粒子较小之样品；通过1000℃烧结和添加CeO2的方法，获得了密度较高、气孔率合适的固相源块；将单畴GdBCO超导块材中的Gd211粒子从10-20微米细化到了2-3微米以下，提高了样品的磁通钉扎力和超导性能。直径20 mm单畴GdBCO超导块材在77K零场冷条件下的磁悬浮力达54.5 N，捕获磁通密度达1.11 T，较TSMTG法单畴YBCO超导块材的0.68 T高63.2%。通过MgO掺杂将NdBCO籽晶的熔化温度提高了10℃以上，增强了籽晶的稳定性和可靠性。通过Li2O和ZrO2掺杂，均提高了单畴GdBCO超导块材的磁通钉扎力和超导性能。研究了多籽晶对大尺寸单畴GdBCO超导块材的影响，不论是采用单籽晶还是多籽晶，均可制备高质量GdBCO块材，样品的GdBCO晶畴数与籽晶数目一致，无随机成核；但样品磁畴个数与籽晶数不一定相同；从实验和理论上阐明了籽晶数目和样品厚度对其性能的影响机制。制备的外径32 mm内径10 mm的单畴GdBCO超导环在77K零场冷条件下的屏蔽磁场达0.4 T。通过预磁化的方法，提高了单畴超导块材的磁悬浮力。建立了计算圆柱形超导块材捕获磁场分布的模型和方法，计算了圆柱形单畴SmBCO超导块材在三维空间的捕获磁场分布，与实验结果吻合很好；获得了单畴REBCO超导块材的捕获磁场与其半径和厚度的关系，样品的直径和厚度越大，捕获磁通密度越高；当样品的径高比合适时，即可获得较好捕获磁通.这些结果为制备高质量单畴REBCO超导块材提供了新思路。