The Impact On Bi-based Superconducting Oxides Microstructure And Properties With Ni-doped

This article made different amounts of Ni-doped Bi-based oxide superconducting powder by Pechini sol-gel method. Samples of precursor powder preparation time for bath and the different sintering temperature on the quality of the Bi system superconducting oxide powder was studied, improved the Pechini sol-gel preparation Bi powder in the process. Based on this study, microstructure and physical properties of Bi-2212 powder with different amount Ni doped in Sr site have been researched. Specific contents of this paper can be divided into the following:Using Pechini sol-gel method make Bi2Sr2-xCaCu2NixO8+δ superconducting powder.The precursor powder samples were prepared by two processes, one is first using the bath and then paraffin bath and the other is paraffin bath without water bath direct. We found that when other conditions are the same, through a water bath heated sample quality is better. When sintering precursor powder,we using 835℃,850℃ and 855℃ three different temperatures, thermal sintering time is 5h. Through the X-ray diffraction pattern, we find sintering temperature is 850℃, the purity of the sample obtained is the best.Under the condition of sintering temperature is 850℃, holding 5 h make the Ni doped in Sr site Bi-2212 (Ni doping amount to x=0.05 to 0.25) superconducting powder samples By analyzing the changes in the diffraction peaks with different amount Ni doped, we can find when x=0.15, the diffraction peak of the three planes (002), (008) and (0010) offset to the Horn is maximum, and the diffraction peak (113), (115), (117) and (020) plane is just the opposite.Indicates that the Ni get into Bi-2212 lattice, and makes the lattice parameter changes. We can also see all the samples of NiO phase peak exists in the XRD spectrum, show all Ni did not enter into the crystal lattice, the remainder of the Ni exists in the form of NiO.Through the four-probe method to measure the resistance of different amount Ni doped sample variation with temperature, a detailed study of the effects of different amounts of Ni-doped samples electricity transport capacity. We found that the Tc of x=0.15 sample, is minimal, while the Tc of other x value samples, onset or less, indicating that the x=0.15 samples,Ni braced lattice structure is the most. And x=0.25 reduce the size of the largest, this is due to the effect of NiO phase, reduce the temperature to a certain extent resistance increased first and then decreased, with a certain extent delayed the superconducting transitionBy the measurement system (MPMS) under the 10 k and 20 k temperature respectively, the hysteresis loop of the sample with different x value was measured,we found that the samples under the temperature 10k showed a large hysteresis loop (△M value is larger), and showed good and uniform superconductivity. On the basis of the measured hysteresis loop, the critical current density of different amount Ni doped sample can be calculated using the Bean model. It can be seen,with different amount Ni doping, Bi2Sr2-xCaCu2NixO8+δ (x= 0.05-0.25) superconducting critical current density variation with powder magnetic field. That is, with the positive direction of the applied magnetic field increasing,the critical current is reduced. Similarly, we found that the amount of Ni doping x= 0.25, obtained largest critical current density. This is mentioned before, the sample of x= 0.25 with the maximum intensity of the pinning, the pinning strength is proportional to the MR, when x= 0.25 it can obtaine the critical current density with greater value. Under the condition of the same magnetic field, with x from the minimum value 0.05 increased to a maximum of 0.25, The critical current density of Bi2Sr2-xCaCu2NixO8+δ superconducting powder showed the basic trend of gradually increasing. The reasons for this result is the pinning effect of NiO phase in the powder, increases with the increase of Ni doping amount.