铝掺杂对MgB2超导电性的影响
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摘要
本论文主要分两部分内容。
第一部分主要介绍了超导的发展、超导电性的基本性质、BCS理论及其主要结论。2001年超导转变温度高达39K的金属间化合物MgB_2的发现激起了物理学界、材料界和工业界的广泛关注，我们简要地分析了MgB_2的超导特性、超导机理及几年来研究现状和应用前景。众所周知掺杂是研究超导材料性能的变化，寻找新超导材料的常用方法。主要说明了采用改进的固相反应烧结法制备了一系列Mg_(1-x)Al_xB_2(0.00-0.15)超导材料，并对它们的结构、转变温度和超导特性作了研究。发现随着Al掺入量的增加晶格参数及临界转变温度都有减小的趋势。结合XRD分析，发现大部分Al原子替代了Mg原子。本文对此现象的产生原因作了分析，结果表明可能是Al原子引起的缺陷和样品中Al分布不均匀所形成的MgAlB_4及反应生成的Al_2O_3共同对超导电性产生了影响。
第二部分介绍了分子拓扑指数理论及分子拓扑指数在材料研究中的预测能力、实用价值和几种典型、重要的拓扑指数。分子和原子的拓扑性质是分子和原子固有的几何性质，它可以反映分子和原子结构的重要信息，这将有助于我们对物质的性质进行预测。通过研究MgB_2掺杂体系的临界转变温度与电负性拓扑指数和价电子轨道能量拓扑指数的0阶指数和之间的关系，发现转变温度高的物质在最佳掺杂范围内对应的和分别在2.9034-2.9509和3.9218-3.8613内。这就为通过实验手段改变MgBcTmFmV~0F~0V~0F~0V2体系掺杂成份，保证了掺杂时掺杂物的选取及浓度大小以保证转变温度的提高，为实验工作者今后探索更好的掺杂MgB_2体系超导物的研究提供了一个借鉴。
The work consists of two parts.
The first part introduces the history of superconductivity, the basic properties of superconductivity and BCS theory and its main conclusions. It also reviews the studies characteristics and mechanism of superconducting and current research and application prospects on MgB_2 during the last few years, for the recent discovery of superconductivity in MgB_2 at temperature as high as 39K has generated great interest in theoretical and experimental fields. Doping is a commonly method used to study the changes in superconducting properties, search for new superconducting materials. In this paper, the improved solid-state reaction method has been used to prepare a series of Mg_(1-x)Al_xB_2 (0.00-0.15) superconductors, and their structure, transition temperature and properties were studied. Found with the increase in Al, lattice parameters and decreased. Combination of XRD analysis, we found a number of Al atoms replace Mg atoms. In this paper, the cause of this phenomenon are analyzed, the impact of superconductivity my caused by the creation of defects by Al atoms and uneven distribution of MgAlBcT4and the reaction of Al_2O_3.
The second part describes the basic theory of molecular topological index and its practical value and predictive power. We know that topological properties of molecular and atomic molecular and atomic inherent geometric properties, which can reflect the molecular and atomic structure of important information, which will help us to predict the nature of the material. We researched the relation of the doping MgB_2 with electronegativity index mF and the valence electron orbit energy index mV of doping MgB_2. It was found the transition temperature of the material in the high range in the optimum doping corresponding to 2.9034-2.9509 and 3.9218-3.8613, respectively. This means changes to the experiment doped components, ensuring the doping concentration of dopant selection and to ensure the transition temperature increase for the experimental workers in the future to explore better system of doping MgB_2 superconducting properties of providing a reference.
第一部分主要介绍了超导的发展、超导电性的基本性质、BCS理论及其主要结论。2001年超导转变温度高达39K的金属间化合物MgB_2的发现激起了物理学界、材料界和工业界的广泛关注，我们简要地分析了MgB_2的超导特性、超导机理及几年来研究现状和应用前景。众所周知掺杂是研究超导材料性能的变化，寻找新超导材料的常用方法。主要说明了采用改进的固相反应烧结法制备了一系列Mg_(1-x)Al_xB_2(0.00-0.15)超导材料，并对它们的结构、转变温度和超导特性作了研究。发现随着Al掺入量的增加晶格参数及临界转变温度都有减小的趋势。结合XRD分析，发现大部分Al原子替代了Mg原子。本文对此现象的产生原因作了分析，结果表明可能是Al原子引起的缺陷和样品中Al分布不均匀所形成的MgAlB_4及反应生成的Al_2O_3共同对超导电性产生了影响。
第二部分介绍了分子拓扑指数理论及分子拓扑指数在材料研究中的预测能力、实用价值和几种典型、重要的拓扑指数。分子和原子的拓扑性质是分子和原子固有的几何性质，它可以反映分子和原子结构的重要信息，这将有助于我们对物质的性质进行预测。通过研究MgB_2掺杂体系的临界转变温度与电负性拓扑指数和价电子轨道能量拓扑指数的0阶指数和之间的关系，发现转变温度高的物质在最佳掺杂范围内对应的和分别在2.9034-2.9509和3.9218-3.8613内。这就为通过实验手段改变MgBcTmFmV~0F~0V~0F~0V2体系掺杂成份，保证了掺杂时掺杂物的选取及浓度大小以保证转变温度的提高，为实验工作者今后探索更好的掺杂MgB_2体系超导物的研究提供了一个借鉴。
The work consists of two parts.
The first part introduces the history of superconductivity, the basic properties of superconductivity and BCS theory and its main conclusions. It also reviews the studies characteristics and mechanism of superconducting and current research and application prospects on MgB_2 during the last few years, for the recent discovery of superconductivity in MgB_2 at temperature as high as 39K has generated great interest in theoretical and experimental fields. Doping is a commonly method used to study the changes in superconducting properties, search for new superconducting materials. In this paper, the improved solid-state reaction method has been used to prepare a series of Mg_(1-x)Al_xB_2 (0.00-0.15) superconductors, and their structure, transition temperature and properties were studied. Found with the increase in Al, lattice parameters and decreased. Combination of XRD analysis, we found a number of Al atoms replace Mg atoms. In this paper, the cause of this phenomenon are analyzed, the impact of superconductivity my caused by the creation of defects by Al atoms and uneven distribution of MgAlBcT4and the reaction of Al_2O_3.
The second part describes the basic theory of molecular topological index and its practical value and predictive power. We know that topological properties of molecular and atomic molecular and atomic inherent geometric properties, which can reflect the molecular and atomic structure of important information, which will help us to predict the nature of the material. We researched the relation of the doping MgB_2 with electronegativity index mF and the valence electron orbit energy index mV of doping MgB_2. It was found the transition temperature of the material in the high range in the optimum doping corresponding to 2.9034-2.9509 and 3.9218-3.8613, respectively. This means changes to the experiment doped components, ensuring the doping concentration of dopant selection and to ensure the transition temperature increase for the experimental workers in the future to explore better system of doping MgB_2 superconducting properties of providing a reference.
引文
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