THE EFFECTS OF IMPURITY OXIDES ON YBA2CU3O7-X MICROSTRUCTURE DEVELOPMENT

Diffusion-couple experiments in conjunction with scanning electron (SE M) and energy dispersive X-ray analysis were used to determine the eff ect of various oxides on the microstructural development of YBa2Cu3O7- x ceramic superconductors. The interaction of a number of impurity oxi des including SiO2, Bi2O3, Pr6O11, TiO2, SnO2, In2O3 and Sb2O3 resulte d in exaggerated grain growth and domain formation in bulk specimens t hrough a liquid-phase wetting mechanism. Reaction sequencing was deter mined by thermal analysis (DTA) and real-time dynamic X-ray diffractio n. The ability and extent of domain formation for samples coupled with SiO2, Bi2O3, Pr6O11 and TiO2 was determined to be a function of oxyge n partial pressure during sintering as well as of the sintering temper ature in the range 940-degrees-C-980-degrees-C. The use of Bi2O3 coupl ed to pre-oriented samples (i.e. hot forged) resulted in extensive dom ain growth at 980-degrees-C. The presence of SiO2 in conjunction with hot forging resulted in a lower magnetization response, due to the pre sence of larger 211 particles and or extensive cracking during sinteri ng.