Synthesis and characterization of YBa2Cu3-xSbxO7-delta high-temperature superconductors

The effects of Sb doping on YBa2Cu3O7-delta high-temperature superconductor s have been investigated. Samples were synthesized for the nominal composit ions of YBa2Cu3-xSbxO7-delta where x = 0.0-0.3 by solid-state preparative t echniques. These materials were prepared under different conditions, such a s heating in an air or an oxygen dow followed by furnace cooling or quenchi ng in air or in liquid nitrogen. These results show that for the air-quench ed samples these materials are superconducting when 0.01 less than or equal to x less than or equal to 0.1, whereas for the furnace-cooled samples T-c gradually decreases with increasing Sb concentration. However, in both cas es zero resistance was not achieved down to 72 K when x greater than or equ al to 0.2. To understand the effects of Sb doping on the structure of YBa2Cu3O7-delta x-ray absorption spectroscopy, x-ray diffraction and scanning electron micr oscopy have been applied. These results indicate that the valence state of copper is almost the same in the pure and the doped YBa2Cu3-xSbxO7-delta. I t has been observed that doping with low concentrations of Sb (x less than or equal to 0.1) and slow cooling have similar effects on the structure of YBa2Cu3O7-delta, i.e. these help to stabilize the orthorhombic structure. W hereas, with higher concentrations of Sb (x greater than or equal to 0.2), all compositions of Liquid-nitrogen-quenched YBa2Cu3-xSbxO7-delta and air-q uenched pure YBa2Cu3O7-delta stabilize in the tetragonal geometry. In super conducting materials the particles are smaller, uniformly distributed and t he grains are linked together, whereas in non-superconducting materials the particles are larger and the grains are not well connected.