Structural And Properties Of YBa₂Cu₃O_7-? Superconducting Composite Films Doped With BiFeO₃ And LaAlO₃

YBa₂Cu₃O_7-??YBCO?superconducting thin films have great application prospect in the fields of electric energy transmission,clean energy development,military defense,physical exploration and magnetic levitation technology.Introduce other materials into YBCO and prepare composite films is one of the most commonly scientific research methods used in the direction of electrical energy transmission.There are many kinds of miscellaneous materials that can be introduced in YBCO.Therefore,it is of great significance to carry out the preparation of YBCO composite film and investigate structure and properties on the basis of the predecessors.The content of this thesis is as follows:YBCO thin film with epitaxial structure and high transition temperature?higher than 88K?was fabricated on a single-side polished single crystal STO?001?substrate at 840 ^oC by pulsed laser deposition method?PLD?.BFO:YBCO composite films with BFO volume fraction of 1.5%,3.0%,4.5%,6.0%and 7.5%were prepared by magnetron sputtering and pulsed laser co-deposition method.The quality of the composite films is good and the particles are evenly distributed.With the increase of BFO volume fraction,the size of surface particles gradually decreases.Zero-resistance transition temperature(T_c0)of samples was obtained by four-probe method and magnetic measurement method.The T_c0 of the pure YBCO was 90.0 K and the T_c0 of the composite films was 89.5 K,88.0 K,87.0 K,85.0 K and81.0 K,respectively.The dependence between the critical current density and magnetic field of the samples with high T_c0 was obtained by PPMS comprehensive test system.It was found that the introduction of BFO increased the critical current density of YBCO.At 65 K and 77 K,the critical current densities of the composite films increase at low magnetic field compared with the pure YBCO sample,while it decay faster at high magnetic field.The dependence between the flux pinning force and magnetic field of the composite films was obtained by data calculation.The pinning mechanism at different temperatures was studied.It was found that the?l pinning and stress pinning played a role in low temperature.The pinning mechanism at 40 K was dominated by?l pinning,the pinning mechanism was dominated by stress pinning at 65 K and 77 K.La AlO₃?LAO?has been introduced into YBCO by magnetron sputtering and pulsed laser co-deposition method.The structure and properties of LAO:YBCO composite films were studied.The composite films with LAO volume fraction of 1.5%,3.0%,4.5%,6.0%and7.5%were prepared on single-side polished STO?001?substrates,respectively.The quality of the composite films is good and the particles are evenly distributed.With the increase of LAO volume fraction,the size of surface particles gradually decreases.The T_c0 of the composite films were 89.5 K,88.0 K,86.5 K,85.0 K and 81.0 K,respectively which is characterized by the four-probe method and the magnetic measurement method.At 65 K and 77 K,the critical current densities of the composite films increase at low magnetic field compared with the pure YBCO sample,while it is lower than pure YBCO sample at high magnetic field.It can be concerned that the maximum flux pinning force of the LAO:YBCO composite films were reduced at 65 K and 77 K.