CRITICAL-CURRENT DENSITY AND MICROSTRUCTURE OF MELT-PROCESSED YBA2CU3OX WITH PTO2 ADDITIONS

YBa2Cu3Ox (123) with excess Y2BaCuO5 (211) in the molar ratio of 5:1 (123/211) were processed using the SLMG (''solid-liquid melt growth'') technique. The effect of PtO2 on the microstructure and properties of samples with coarse (approximately 1-10 mum) and fine 211 precipitates (on the order of 100 nm) was studied. PtO2 leads to a decrease in the total volume of the coarser 211 precipitates and segregation of these 211 particles, forming ''tracks'' of the precipitates within a domain. Also, the morphology of the coarse 211 phase changed to a long acicular shape with PtO2 additions, as compared with approximately spherical particles in undoped samples. TEM studies revealed the presence of 211 particles of approximately 100 nm size in both doped and undoped samples with a density of 10(13)/cm2 along with the coarser 1-10 mum 211 particles. The defect density was found to be higher in the case of PtO2 doped samples. The intragrain J(c) measured on powdered textured specimens was found to be enhanced by the PtO2 additions, especially at low temperatures, despite the fact that the coarser 211 precipitates were inhomogeneously distributed. Magnetization measurements on textured domains also showed an improvement of J(c)(H parallel-to c at 1 T) with PtO2 doping, corroborating the measurements on the powdered samples.