Al-doping Effects On The Superconductivity Of MgB₂

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 MgB₂ during the last few years, for the recent discovery of superconductivity in MgB₂ 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-xAl_xB₂ (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 Al₂O₃.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 MgB₂ with electronegativity index mF and the valence electron orbit energy index mV of doping MgB₂. 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 MgB₂ superconducting properties of providing a reference.