THE EFFECTS OF IMPURITY OXIDES ON YBA2CU3O7-X MICROSTRUCTURE DEVELOPMENT

Diffusion-couple experiments in conjunction with scanning electron (SEM) and energy dispersive X-ray analysis were used to determine the effect of various oxides on the microstructural development of YBa2Cu3O7-x ceramic superconductors. The interaction of a number of impurity oxides including SiO2, Bi2O3, Pr6O11, TiO2, SnO2, In2O3 and Sb2O3 resulted in exaggerated grain growth and domain formation in bulk specimens through a liquid-phase wetting mechanism. Reaction sequencing was determined by thermal analysis (DTA) and real-time dynamic X-ray diffraction. The ability and extent of domain formation for samples coupled with SiO2, Bi2O3, Pr6O11 and TiO2 was determined to be a function of oxygen partial pressure during sintering as well as of the sintering temperature in the range 940-degrees-C-980-degrees-C. The use of Bi2O3 coupled to pre-oriented samples (i.e. hot forged) resulted in extensive domain growth at 980-degrees-C. The presence of SiO2 in conjunction with hot forging resulted in a lower magnetization response, due to the presence of larger 211 particles and or extensive cracking during sintering.