Microstructure and properties of MOCVD-derived Gd_xY_(1-x)Ba_2Cu_3O_(7-δ) films with composition fluctuations

摘要

The effects of Gd content on crystalline orientation,microstructure and superconductivity of Gd_xY_(1-x-)Ba_2 Cu_3 O_(7-δ)(GdYBCO) films were systematically investigated.By varying the Gd content in the liquid precursor without changing the total amount of rare earth elements,series of GdYBCO films with x values of 0,0.1,0.3,0.5,0.7,0.9 and 1.0 were fabricated by metal organic chemical vapor deposition(MOCVD).X-ray diffraction(XRD) and scanning electron microscope(SEM) analysis revealed that Gd introducing could restrain the formation of CuYO_2 phase,but induce a-axis growth of GdYBCO film.The increase of x from 0 to 0.5 leads to enhancing critical current density at self-field and 77 K(J_(csf)) from 1.8 to 2.8 MA cm^(-2).which benefits from the decrease in CuYO_2 impurities and improvement of in-plane texture from 5.0° to 4.3°.However,raising × from 0.5 to 1.0 gives rise to abundant a-axis growth of film and degradation of in-plane texture from 4.3°to 5.4°,consequently resulting in the decrease of J_(csf) from 2.8 to 0.8 MA cm^(-2).Even though J_(csf) has not varied monotonically,the critical transition temperature of GdYBCO films linearly increases from90.75 to 92.25 K and the in-field performance at magnetic field(B) of 0-1.1 T and 77 K as well as B parallel to film normal is also superior with Gd content increasing.