用新液相和新固相制备单畴织构GdBCO超导块材的新方法及机制研究

Single domain GdBCO bulk superconductor is one of the most important materials for high technology applications, because of its high levitation force and tapped magnetic field. Top seeded infiltration and growth process (TSIG) is one of the most main important methods for fabrication of single domain GdBCO bulks with controllable geometric shape and high perfomance, but there are still some problems, such as too many experimental procedures, complicated synthesis mechanism and fabriction process, uncontrollable of the size and distribution of the Gd2BaCuO5（Gd211）particles. Our project, based on the traditional TSIG method, will focus our attention on detail innovations, explore new ways and synthesis mechanism, the main research is: 1) the infiltration characteristic and physical mechanism between the new liquid phase and the new solid phases, when the temperature is higher than the melting temperature of the new liquid phase. 2) the phase transition and chemical reaction mechanism between the absorbed new liquid phase and the new solid phases at the temperatures above but near the peritectic temperature of GdBCO superconductors; and explore new methods and mechanism to obtain nanometer Gd211 particles with reseanable distribution. 3) To investigate the crystal growth dynamics, microstructure and physical properties of the GdBCO bulk superconductors. Finally, we will make clear the new heterogeneous phase reaction mechanism and crystal growth mechanism of the GdBCO bulk superconductors by using the new liquid phase and the new solid phases; and establish a new way and new research direction for fabrication of single domain GdBCO bulk superconductor with low cost, high efficiency and high quality.

大的磁悬浮力和强的磁通捕获能力使单畴GdBCO超导块材已成为国际上研究的重点和热点。但目前用于制备单畴GdBCO超导块材的顶部籽晶熔渗生长法(TSIG)，却遇到了亟待解决的关键问题：现有的方法1).以纯Gd2BaCuO5（Gd211）为固相源，很难控制样品中Gd211粒子的含量及粒度大小，严重影响样品质量的提高；2).至少需要制备2种或3种粉体，合成机制复杂、制备周期长、成本高、效率低。本项目将优化粉体合成机制，发明新固相源和新液相源，并深入研究：1)新液相源熔化渗入新固相的规律及其物理机制；2）渗入的液相与新固相在不同温区的多相反应机制，探索微纳尺度Gd211粒子生成的新方法和机制；3）用新方法制备单畴GdBCO超导块材的晶体生长动力学规律及其超导性能。在此基础上，建立有自主知识产权的制备单畴GdBCO超导块材的新方法，为高效率、低成本、制备高质量单畴REBCO超导块材提供新思路。

本项目以Gd2O3+xBaCuO2为新固相源代替传统的Gd2BaCuO5（Gd211）固相源，采用顶部籽晶熔渗生长方法，研究了制备单畴GdBCO超导块材新方法。主要结果如下：1).通过对新固相源Gd2O3+BaCuO2和传统固相源坯块在不同温度下的固相反应和Gd211晶粒生长规律研究发现，随着烧结温度的升高，Gd211粒子均逐渐长大；但传统固相源中的Gd211粒子粗化速度明显偏快、Gd211晶粒更大、密度更高（密度高达6.41 g/㎝3@1150℃）、相邻晶粒已长在一起、形成了不同尺度的Gd211晶粒群，这些Gd211晶粒群相互连接、形成了间隙很小的网状结构，不利于液相的溶渗；而新固相源样品中的Gd211粒子粗化速度明显偏低，且Gd211晶粒较小、致密性较低（密度约4.93 g/㎝3@1150℃）、生成了Gd211晶粒群相互连接、间隙较好的网状结构，有利于液相的溶渗。2).通过对新固相源Y2O3+BaCuO2与传统固相源Y2BaCuO5样品的差热分析发现，新固相源样品有三个反应峰，而传统固相源样品则有四个反应峰，说明新固相源减少了化学反应环节；同时发现，新固相源样品的包晶反应温度比传统固相源低约4℃，这有效地拓宽了晶体的生长温度窗口。3).通过淬火的方法，研究了用新固相源Gd2O3+BaCuO2替代传统的Gd211固相源后，单畴GdBCO超导块材的晶体生长窗口及其规律，结果表明，单畴GdBCO晶体的生长温度区间为1035℃～1019℃；过冷度越大，晶体的生长速率越快，GdBCO晶体中捕获的Gd211粒子越小；与用传统的Gd211相固相源相比，新固相源可显著提高该类晶体的生长速率。4). 通过新固相源Gd2O3+xBaCuO2组份（x=1～2.5）对单畴GdBCO超导块材生长形貌、微观结构、磁悬浮力以及捕获磁通的影响研究发现，该新方法不仅改变了晶体生长过程中的化学反应机制、而且可有效控制单畴GdBCO超导块材Gd211粒子的含量；当Gd2O3：BaCuO2=1：1.2时，样品的磁悬浮力和捕获磁场强度均达到最大值；5). 我们还研究了Ni2O3等化学掺杂对新TSIG法制备单畴GdBCO超导块材性能的影响，并取得了很好的效果。在此基础上，建立了有自主知识产权的制备高质量单畴GdBCO超导块材的新方法。