Study Of Doping Of Ce And La Of Nanoscales YBa₂Cu₃O_7-δ And The Doping Choice Of YBa₂Cu₃O_7-δ

YBa₂Cu₃O_7-δ superconductor has widely studied due to its lower ac loses, better in-field performance, high irreversibility fields and lower processing costs, which can be widely used in a few aspects of energy, information, medicine, traffic, national defence, science research, etc. The material of YBa₂Cu₃O_7-δ superconductor is one of the extremely greatest concerns of the material. The Summary of Superconductive Physics was introduced simply in this dissertation at first, the history of superconductivity, basic notions and applications of high temperature supercondu- cting materials were also introduced at the same time. Then, some basic characteris- tics and superconductivity of YBa₂Cu₃O_7-δ and the method of preparation of YBa₂Cu₃O_7-δ and the topological theory were introduced mainly. Considering the importance of the doping of YBa₂Cu₃O_7-δ, this dissertation titled"Study of doping of Ce and La of nanoscales YBa₂Cu₃O_7-δ and the doping choice of YBa₂Cu₃O_7-δ"mainly describes the following work and results:1. Lightly doped Y_1-xCe_xBa_2-xLa_xCu₃O_7-δ(x=0-0.25) nanoparticles have been successfully prepared by the citrate pyrolysis method. The mean crystalline size of annealed samples ranges from 29.25 nm to 74.47 nm, which is calculated by the Scherrer's equation. The microstructures,R-T characteristic,optical absorption properties of the Y_1-xCe_xBa_2-xLa_xCu₃O_7-δ were studied by X-ray diffraction (XRD), the standard four-probe technique, infrared spectroscopy. The XRD measurements showed the material is single phase and have an orthorhombic unit cell(x≤0.0625). The resistivity measurements showed that the doping concentration of the samples is less than 0.0625 have metal acts, showing a good superconductivity, and have a sharp one step transition, the samples (0.11≤x≤0.25) metal-insulator transitions at 171. 5K. Three major IR modes at around 594 (A1), 1440 (A2) and 3430 (A³) cm -1 have been clearly observed. It is found that the infrared spectroscopy band at around 594(A1) cm-1 corresponding to c-axis symmetrical stretching mode and the in plane Cu–O asymmetrical stretching mode, respectively. 2. According to existing experiments of the doping YBa₂Cu₃O_7-δ, the relation of lattice parameter with superconductivity of the doping YBa₂Cu₃O_7-δ was studied. The results show that: the transition temperatures of doping YBa₂Cu₃O_7-δ system increase first and then decrease with the increase of lattice parameter a, b, c and crystal volume V, in which a, b can be divided into two regions to discuss when b is less than 3.8728 A when the trend showing a decline. Most-doped YBa₂Cu₃O_7-δ system, their lattice parameters a focus on the numerical 3.8129 A～3.8858 A, b on the 3.8146 A～3.8902 A, c focus on 11.6540 A～11.6985 A, crystal volume V mainly concentrated in the value 172.4824 A³ï½ž174.6539 A³. Comparatively, doped YBa₂Cu₃O_7-δ system, the lattice parameter a to be closer 3.8230 A and 3.8822 A, b is closer 3.8207 A and 3.8830 A, c is closer 11.6985 A, the crystal volume V closer 173.1785 A³ the doping effects to be better. The crystal structure of superconductors are closely related to their superconductivity, so these results give a good reference to conduct the study on the superconductivity of doping YBa₂Cu₃O_7-δ.3. Using the valence electron orbit energy ( Ei ) and number of valence electron shell ( ni ) , a new connectivity topological index (mE) was proposed fromδi. Studying the relation of the 0 order of index with Y series, Bi series oxide superconductors, an empirical rule is found. Y series oxide superconductors 0E value are between 13.9536 and 16.1452, which showed good superconductivity. Bi series oxide superconductors 0E value concentrated in the value 15.8045～16.3455 and 19.5900～20.3772, also showed good superconductivity. It is suggested that the Topological Index mE of Valence Electron orbit energy can be used as a empirical criterion for the superconductivity of Y series, Bi series oxide superconductors, It has a good instruction significance to the researchers on synthesizing Y series, Bi series oxide superconductors of the higher Tc.