PRELIMINARY-STUDY ON FORMING PREFERENTIAL ORIENTATION IN TL-1223 BULKSUPERCONDUCTOR

It was reported [1] that a preferential c-axis orientation exists in T l-1223 bulk superconductor with a nominal composition of (Tl0.5Pb0.5)S r0.8Ba0.1)(2)Ca2Cu3Oz. Now the condition under which the preferential orientation can form and the factors which lead to preferential orient ation have been investigated. The results indicated that, in the (Tl0. 5Pb0.5)(Sr2-xBax) Ca2Cu3Oz system with Sr content increasing and Ba co ntent decreasing, the distance between atoms in the a-b-plane shortens more drastically than that between adjacent atoms along the c-axis, a nd when x decreases to 0.2, the bond strength between atoms in the a-b -plane becomes much stronger, and then the crystalline grains grow pre ferentially in the a-b crystallographic direction and show a plate-lik e shape. Later, these platelets realign at the partial-melting stage d ue to the existing liquid phase, so the preferential c-axis orientatio n is obtained.