INFLUENCE OF IRON DOPING ON THE MICROSTRUCTURE OF YBA2(CU1-XFEX)3O7-DELTA CERAMICS

Porosity, grain growth, phase composition, and microstructural defects were studied in sintered YBa2(Cu1-x)Fex)3O7-delta ceramics for x valu es up to 0.3. The porosity of the samples, related to the sintering me chanism, was independent of iron concentration. A linear dependence of the grain size with the inverse of the iron concentration was found, strongly suggesting grain boundary segregation of iron. The solubility limit was estimated to be x = 0.18 at 950-degrees-C in O2. Beyond thi s limit, a new microstructural component was found consisting of Yba2( Cu1-xFex)3O7-delta YBaCuFeO5 and Ba(Cu,Fe)O2. The transition from an o rthorhombic twin to an orthorhombic tweed phase and a tetragonal phase was detected by polarized light microscopy.