| REBCO superconductors,possessing high critical transition temperature(Tc)and critical current density(Jc),have been widely investigated by scientists since its discovery.As we know,the quality of the REBCO film is seriously affected by many factors,such as the growth condition,the buffer layer and the applied magnetic field.Therefore,we improved the properties of the REBCO film by modifying the buffer layer and searching dopant.The main results and innovations are listed below.1.Fabrication of Homo-Mg O layer and its effect on the Ce O2 film.Homoepitaxial Mg O(Homo-Mg O)films,were fabricated by RF magnetic sputtering method on the IBAD-Mg O films.The results showed that high quality Homo-Mg O films were obtained at high oxygen partial pressure and the thickness of Homo-Mg O films were seriously dependent on the ratio of O2/Ar.However,unlike the usual case,the quality of the Ce O2 film was not linearly dependent on the texture of Homo-Mg O film.The lattice distortion of the IBAD-Mg O film took responsibility for this phenomenon.The lattice constant changed from 4.217(?)to 3.796(?).Finally,using pulsed laser deposition technique,high c-axis oriented Ce O2 film with the in-plane full width of half maximum(FWHM)of 2.78°was fabricated on the Homo-Mg O layer for the first time.2.Enhanced superconductivity by inserting the STO inter-layer.Using a reel-to-reel PLD system,the YGd BCO/STO/YGd BCO multi-layers were fabricated successfully and the thickness effect of the YGd BCO film was restrained by the STO layer.As we know,the growth of the crystalline grain,resulting in the large grain boundary,caused the thickness effect of the REBCO films.By inserting a STO layer,a re-nucleation phenomenon occurred,suppressing the further growth of the large grains.In theory,the current cannot pass through the STO layer because of its insulating feature,while the metal particles embedded in the STO films become the current transfer channels.Besides,we were also able to grow not-fully-coved STO film as the buffer layer,which could not only suppress the thickness effect,but also allow current transfer.3.Superconducting properties of Ce O2-YBCO and La2O3-YGd BCO films fabricated by pulsed laser deposition.Using a reel-to-reel pulsed laser deposition(PLD)system,the Ce O2-doped YBa2Cu3O7-?(Ce O2-YBCO)and La2O3-doped Y0.5Gd0.5Ba2Cu3O7-?(La2O3-YGd BCO)films were fabricated.The results showed that the relationship between the critical current(Ic)values and the deposition temperature depended on the doping content essentially.For all Ce O2-doped films,the Ic values increased at first and then decreased with increasing the deposition temperature.The substitutions of the Y atoms by Ce atoms are considered as the determinative factor.While,the high-doped La2O3-YGd BCO film was obtained with high Ic.That is because,different from the Ce BCO,the La BCO is also a superconductor.That is to say,the substitutions of the Y atoms by La atoms have little influence on the Ic values.4.Melting behavior and superheating capacity of REBa2Cu3Oyfilms with nano-layer buffered structures.Using high temperature-optical microscopy,in situ investigations were conducted on melting and superheating behaviors of REBCO(RE=Nd,Gd)films,which were grown on nano-layer buffered substrates.The results demonstrated that all buffered REBCO films had improved crystallinity and in-plane alignments,leading to the higher superheating capability.Due to its good lattice match with the buffer material,the REBCO film with the minimal extrinsic property grew from the superior interface.Moreover,the optimized thickness of buffer layer played an important role in reducing interface energy of REBCO films and enhancing its superheating capacity.In conclusion,by adding impurity and modifying buffer layer,the Ic value of the REBCO film was improved successfully.Besides,a proper seed material was found by studying the superheating phenomena. |
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