Effects of Vertical Temperature Gradient on the Growth Morphology and Properties of Single Domain YBCO Bulks Fabricated by a New Modified TSIG Technique

Abstract

Single domain YBCO bulk superconductors have been fabricated with different vertical temperature gradients (VTG) by a modified top-seeded infiltration and growth (TSIG) process with a new solid phase (Y2O3+BaCuO2) and a new liquid phase (Y2O3+6CuO+10BaCuO2). It is found that the angle α (between the upper surface and interface of a- and c-growth sectors) is very sensitive to the VTG, which means that the growth rate in c-axis direction (Rc) can be changed by the VTG, according to tan α = Rc/Ra; Ra is the growth rate in the a-axis direction. It is also found that the 4-fold growth sectors did not cover the whole surface of the sample grown with a positive VTG, and the volume fraction of the single c-axis growth sector (Vfc) is 37.5% of the sample grown with a zero VTG, but it is reduced to 25% by a positive VTG, and enlarged to 53.6% by a negative VTG. The results of levitation force and trapped field of the samples show that a negative (or positive) VTG can improve (or reduce) levitation force and trapped...