Co-doping Effects Of Calcium And Cerium On The Superconducting Properties In YBa₂Cu₃O_7-δ

YBa₂Cu₃O_7-δ（YBCO,Y123） is a copper oxide high-temperature superconduc-tors with perovskite structure, and it has significant application prospects in the fieldof energy, electricity, transport, electronic communications, medical, scientificinstruments, defense and major scientific and technological projects. YBCO is one ofthe most studied and most widely used superconductors in high-temperaturesuperconducting materials. Moreover, doping is a very effective measure that widelyused in exploring the mechanism of high temperature superconductivity, improvingthe material properties and searching for new superconducting materials. The dopingnot only can improve the microstructure, superconducting properties and phase ofsuperconducting materials, but also can influence the thermodynamic behavior of thecrystal growth and improve the mechanical properties of superconductors. Therefore,the main content of this paper is co-doping effects of calcium and cerium on thesuperconducting properties in YBa₂Cu₃O_7-δ.This paper includes the following aspects:Firstly, an overview of the high-temperature superconducting materials, specialconstruction and application of YBCO superconducting materials, current researchand contents and purport of the paper were simply introduced in the dissertation. Then,several common preparation techniques and characterization methods of YBCO wereintroduced. At the same time, preparation method and characterization methods of ourexperiment sample were explained clearly in this paper.Secondly, the effects of calcium and cerium co-doping in YBa₂Cu₃O_7-δon thesuperconducting properties was studied deeply, and we did detailed theory analysis tothe experiment result. The conclusion as follows:1. YBa₂Cu₃O_7-δsuperconductor was prepared by a modified solid-state reactionmethod through grind and calcine several times, and its superconductivity wascharactered. XRD indicted that the main phase of pure sample is Y123phase except alittle inevitable carbon and other foreign phases. The sample of superconductivity wasmeasured using normal four terminals method. The result indicated that the onsetsuperconducting transition temperature was92.02K, and the transition width is2.98K, which was decreased2K than the transition width of5K using the conventional solid state reaction method. So it was a good method to prepare a goodsuperconducting property of YBCO sample.2. A series of Y_1-xCa_x(Ba_1-xCe_x)₂Cu₃O_7-δ（x=0⁰.3） superconductor samples wereprepared by a modified solid-state reaction method. With the increase of Ca and Cesubstituting quantity, the content of Y123phase gradually decreased, but the contentsof BaCeO3phase and Y211phase gradually increased. When x=0.3there wasn’t Y123phase, and the sample lost superconductivity. The reason was that Ce did notsubstitute for Ba site to form the superconducting structure, but form the impurityphase of BaCeO3. At the time, the onset superconducting transition temperature ofsamples decreased from92.02K for the sample to77.53K, and the transition widthbecame shaper. There were an increase in a-axis and c-axis lattice parameters and adecrease in b-axis lattice parameter with increasing Ca and Ce. In addition, the aparameter and the b parameter had a tendency to close to the value of3.86, and itmeant that the crystal structure changed from orthorhombic crystal system totetragonal crystal system with increasing Ca and Ce.3. A series of polycrystalline samples of Y_1-xCa_x（Ba1-yCey）₂Cu3O7-δwere preparedby a modified solid-state reaction method. When Ca alone doping in samples （y=0）with increasing x, the onset superconducting transition temperature decreased and thetransition width becomes broader. This result implied that the intergrain connectivitydecreased by solitary Ca doping. For the Ce doped samples （y=0.02, y=0.04）,although the onset superconducting transition temperature decreased, the variationtendency was slight, and the broadness of transition width becomes smaller withincreasing x. It came to the conclusion that the Ce doping has an effect forstrengthening the intergrain connectivity, and it counteracts the weakening effect ofCa doping.