MICROSTRUCTURE OF PTO2-DOPED MELT-TEXTURED Y1BA2CU3O7-DELTA

Melt-textured Y1Ba2Cu3O7-delta was processed by the VGF(vertical gradi ent freeze)-method. The precursor had an excess of 25mol% Y2BaCuO5 (21 1) and 1.8mol% PtO2. j(c) of these samples is enhanced compared to mel t-textured Y1Ba2Cu3O7-delta with excess 211 but without PtO2 doping. I n order to understand this enhancement in j(c), a detailed microstruct ural study was performed by transmission electron microscopy. The twin spacings in these samples are reduced to 50-100nm compared to twin sp acings of 200-300nm in melt-textured Y1Ba2Cu3O7-delta without PtO2 dop ing. The PtO2 doping leads to a reduced size (less than or equal to 1 mu m) and an enhanced density (2x10(18)/m(3)) of the 211 particles. Mo st of the 211/123 interfaces are almost clean and free of crystal defe cts. Only a few of them were surrounded by defects like stacking fault s. Therefore, we conclude that the the 123/211 interface is the domina nt pinning center in the PtO2 samples. The Cu required for the stackin g fault formation near the 211 particles originates from the 211 inclu sions as confirmed by EDX.