ZrO_(2)掺杂YBa_(2)Cu_(3)O_(7-δ)超导薄膜的磁通钉扎

Flux pinning study of ZrO_(2)-doped YBa_(2)Cu_(3)O_(7−δ)superconducting films

YBa_(2)Cu_(3)O_(7-δ)(YBCO)超导薄膜的临界电流密度J_(c)会因为外磁场的增大而衰减.为了抑制这一现象,有必要引入人工钉扎中心.预制纳米晶能够实现对异质相大小和形状的预先调控,是一种非常高效的人工钉扎手段,能有效解决传统元素掺杂引起的尺寸和团聚问题.本文利用水热法可控地制备出两种尺寸小于10 nm的点状和棒状ZrO_(2)纳米晶,并采用葡萄糖酸对其表面进行修饰,实现它们在YBCO前驱液中的均匀单分散.单分散ZrO_(2)纳米晶的掺杂明显地提高了YBCO薄膜的低温磁通钉扎效果和在场临界载流性能,但是纳米晶掺杂量过多,又会因为生成BaZrO_(3)(BZO)而消耗过多Ba源,致使YBCO薄膜超导性能下降.另外,掺杂5%的点状ZrO_(2)纳米晶比棒状纳米晶对超导性能提升更优.

The critical current density(Jc)of the YBa_(2)Cu_(3)O_(7−δ)(YBCO)superconducting film will decrease with the increase of the external magnetic field due to the movement of flux vortex.The existence of the magnetic flux movement will cause energy consumption similar to the resistance,which usually can be pinned by different kinds of defects located in the YBCO film.However,the defects formatted during the YBCO film growth alone is not enough for the increasing application requirements.Thus,it is necessary to introduce pinning centers artificially to enhance the in-field critical current capacity.Element doping is one of the most commonly used methods.The metal-organic deposition method is used to generate nano-heterogeneous BaMO_(3)(M is metal,such as Zr,Zn,Hf,etc.)in YBCO films.These heterogeneous phases generally do not produce large texture distortion and can be used as effective flux pinning centers.However,doped heterogeneous phases still have problems such as large doped phase size and uneven spatial distribution of nanoparticles.Although there are some research methods that are conducive to solving the above problems,the ability to control element doping is limited.The addition of the preformed nanocrystals is a very efficient means to introduce the artificial pinning centers,which has the advantage of highly controlling of the shape and size and solving the problem of agglomeration in the traditional elemental doping route.In the present work,two kinds of dot-like and rod-like ZrO_(2)nanocrystals with sizes smaller than 10 nm were controllably prepared by the hydrothermal method.In order to achieve the monodispersive state of the ZrO_(2)nanocrystals in the acidic YBCO precursor solution,their surfaces were modified with gluconic acid.The transmission electron microscope tests revealed that the ZrO_(2)nanocrystals were randomly mono-dispersed in the gel film after coating.Compared with undoped YBCO films,zirconia nanocrystals doping reduces the superconducting critical transition temperature of the films,and the superconducting critical transition temperature decreases with the increase of doping amount,which may be caused by the volume proportion of nanocrystals in the films and the increase of Ba source consumption.The doping of ZrO_(2)nanocrystals significantly improves the low-temperature magnetic flux pinning and the in-field critical current densities of YBCO films.At 65 K,the maximum pinning force density of YBCO films doped with 5%ZrO_(2)-C nanocrystals is about 15.2 GN/m^(3),which is almost twice the pinning force density(7.3 GN/m^(3))of YBCO films without nanocrystals in the same magnetic field.Even at 77 K,the pinning force density of YBCO films increased by 66.6%compared with undoped films after doping with 5%dot-like nanocrystals.However,doping too much will lead to the increasing competition with the growth of the YBCO film due to the consumption of more Ba sources to form the BaZrO_(3)(BZO),resulting in a decline in the quality and superconducting performance of the ZrO_(2)-doped YBCO thin films.In addition,it is revealed that the doping with 5%of the dot-like ZrO_(2)nanocrystals results in a better flux pinning property and in-field performance of the YBCO film than that of the rod-like nanocrystals.