Twin Boundaries in Superconducting YBa2Cu3O7-x: Twin Boundary Energy and Its Dependence on Dopants, Additives, and Processing Parameters for Engineering Fine Twins.

超导 YBa2Cu3O7-x 中的孪生边界：孪生边界能及其对掺杂剂、添加剂和工程精细孪生加工参数的依赖性。

• 批准号: 0214650
• 负责人: Siu-Wai Chan
• 金额: $ 33万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0214650&HistoricalAwards=false
• 关键词: Twin; Boundaries; Superconducting; YBa2Cu3O7; Boundary

Effective pinning of magnetic fluxes is imperative of sustaining critical current. Otherwise a voltage drop is induced by moving magnetic flux lines and resistance develops. It is now recognized that flux-pinning by twin boundaries in YBa2Cu3O7-d (YBCO) exists but is highly dependent on the direction of flux-line motion. Their presence has helped the YBCO to exhibit higher critical current densities at high temperatures and high magnetic fields than those of the Bi, Hg and Tl cuprates despite their higher critical temperatures. It follows that a higher twin density leads to a larger flux-pinning force and a higher critical current density in magnetic fields and temperatures that are more attractive for applications. Yet very few efforts have been in engineering fine twins and twin domains to exploit their flux-pinning properties. Our project is to come up with methods to engineer fine twin structure. To identify these methods, we first need to know the value of the twin boundary energy and its dependence on a number of materials processing parameters. Information on twin boundary energy and its dependence on processing parameters allows the optimization of twin structure by controlling these processing conditions. This information can be exploited to produce the best twin morphology, which leads to maximum flux pinning and high critical current density. Specifically, equipped with the information, we can refine the twin structure in YBCO systematically. This allows the systematic investigation of critical current density (Jc) by magnetization and twin microstructure by microscopy in search for optimal twin structure for enhanced critical current density. Our proposed work will address the twin contribution to flux pinning and critical current density with the goal to obtain the optimal composition, additive, oxygenation and processing conditions for maximum flux pinning and highest Jc. This area of microstructure research is much ignored and can also provide excellent research training for graduate students.Impact: The major problem, for industrial applications of high temperature superconductors, is their low critical-current density (a measure of current that can be transmitted without electrical resistance) caused by poor current transmission at the grain boundaries and insufficient flux-pinning centers at application temperatures and magnetic fields. Twin boundaries in the high temperature superconductor YBa2Cu3O7-d (YBCO) are ubiquitous and have been proved to be effective pinning centers of magnetic fluxes in YBCO for (i) the practical range of operation at temperature ranging from -230 C to -190C and (ii) magnetic fields of the order of 20,000 times of the earth's magnetic field. New methods for engineering twin morphology will emerge from this proposed work that can be applied to YBCO coated tapes which can help to solve the long standing problem of low critical current density of the high temperature superconductors and allow board applications. Twinning as a material phenomenon affects important material properties in ferroelectrics, ferromagnetics, ferroelastics and intermetallic compounds with martensitic-transformation. As such, what we learn from twinning in YBCO, can be directly applied to these technologically important materials to optimize their properties.

有效地钉扎磁通是维持临界电流的必要条件。否则，磁通线的移动会引起电压降，从而产生电阻。YBa2Cu3O7-d(YBCO)中存在孪晶界的磁通钉扎现象，但与磁通线的运动方向密切相关。它们的存在帮助YBCO在高温和强磁场下表现出比Bi、Hg和Tl铜酸盐更高的临界电流密度，尽管它们的临界温度更高。因此，孪晶密度越高，磁通钉扎力越大，在磁场和温度下的临界电流密度越高，这对应用更有吸引力。然而，在设计优良的孪晶和孪生磁区以利用它们的磁通钉扎特性方面所做的努力很少。我们的项目是提出设计精细孪生结构的方法。为了识别这些方法，我们首先需要知道孪晶边界能的值以及它与一些材料加工参数的关系。关于孪晶边界能及其对工艺参数的依赖关系的信息允许通过控制这些工艺条件来优化孪晶结构。利用这些信息可以产生最佳的孪晶形态，从而获得最大的磁通钉扎和高的临界电流密度。具体地说，有了这些信息，我们就可以系统地细化YBCO的孪晶组织。这使得通过磁化来系统地研究临界电流密度(JC)和通过显微镜来系统地研究孪晶组织来寻找提高临界电流密度的最佳孪晶结构。我们提出的工作将解决对磁通钉扎和临界电流密度的双重贡献，目的是获得最优的成分、添加剂、氧化和工艺条件，以实现最大的磁钉扎和最高的JC。这一领域的微观结构研究被忽视了，也可以为研究生提供极好的研究培训。影响：对于高温超导体的工业应用，主要问题是由于晶界电流传输不佳以及应用温度和磁场下磁通钉扎中心不足导致其临界电流密度(可以在没有电阻的情况下传输的电流)较低。高温超导体YBa2Cu3O7-d(YBCO)中的孪晶界是普遍存在的，已被证明是YBCO中磁通的有效钉扎中心，它的实际工作温度范围为-230℃到-190℃，以及(Ii)约为地球磁场20,000倍的磁场。这项工作将为设计孪晶形态提供新的方法，可应用于YBCO涂层带材，有助于解决长期存在的高温超导体临界电流密度低的问题，并使板材应用成为可能。孪生作为一种材料现象，影响着铁电材料、铁磁材料、铁弹性材料和具有马氏体相变的金属间化合物等重要材料的性能。因此，我们从YBCO的孪生中学到的东西，可以直接应用于这些具有重要技术意义的材料，以优化它们的性能。