BENEFITS OF USING A NANOSTRUCTURED TARGET IN LASER ABLATION OF THIN YBCO FILMS

摘要

Nanostructured targets with grain size of about 100 nrn have been used for pulsed laser deposition of YBa_2Cu_3O_(6+x) (YBCO) thin films. The targets were prepared by sintering from nanosized powder (1-3 nm high and 50-100 nm wide particles). Using nanostructured targets in PLD leads to smaller growth islands on the substrates than using micron size grained targets. The smaller growth island size leads to smaller twin domain size and faster relaxation of the twin lattice. The denser defect structure in the nanofilms leads to better pinning and hence higher J_c, even up to 8 MA/cm~2 at 77 K. The pinning can be further enhanced by doping the target with BaZrO_3 (BZO), which improves the high field critical current density of the films with 350 % at 5 K and 5 T. The BZO is found to orient itself with the YBCO lattice and affect the twin lattice relaxation and therefore we believe that the BZO is situated in the growth island boundaries.