Keywords: 
• YBa2Cu3O7-δ /
• Gd掺杂 /
• Raman

Abstract: Recently, the second-generation YBa2Cu3O7-δ(YBCO) high temperature superconducting materials have attracted much attention and become a hot research point. The YBCO coated conductors are widely used in transmission cables, motors, generators and magnetic energy storage systems due to their high critical current densities and high irreversible fields. To obtain high critical current, it is necessary to increase the thickness of YBCO film. However, as the thickness increases, the cracking of the film appears and the a-axis grains form, which causes the critical current density to decrease drastically, hence the critical current declines, i.e., the so called "thickness effect" appears. In order to overcome the"thickness effect", a great many of efforts have been devoted to it. It is realized gradually that the growth orientation of the c-axis can be controlled by the stress of film, which can be achieved through the substitution of Y by Gd and Sm each with a larger ionic radius. However, the systematical study of the evolution of the stress mechanism with the substitution ratio is still lacking due to the extreme complexity of the stress manipulation. Therefore, a series of Y1-xGdxBCO thin films with different substitution ratios is deposited on lanthanum aluminate substrates by the fluorine-free metal organic deposition method in order to reveal the evolution of the stress mechanism with Gd substitution. The growth orientations, microstructures and lattice vibration characteristics of the films are analyzed by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The results show that the lattice constant of the film increases and the orientation of the c-axis changes with the Gd substitution ratio for x increasing to a value less than 0.5, and the blue shift of the O(2/O(3 mode of the Raman spectrum decreases with increasing x. For x=0.5, the blue shift of the O(2/O(3 mode vanishes, indicating the free standing film with optimal c-axis orientation. However, with the further increase of Gd content, the film structure is deteriorated, and the performance is degraded as well. The red shift of the O(2/O(3 mode occurs and the frequency decreases with increasing x. Our results indicate that the stress mechanism can be manipulated by controlling the content of various ionic radii in Y1-xGdxBCO films. The free standing film with optimal c-axis orientation can be obtained through adopting an appropriate substitution ratio, i.e., the ratio of Y:Gd equaling 1:1. These results suggest that manipulation of the stress mechanism is a promising method to overcome the"thickness effect"effectively.