Phase formation and melt processing of Yb-123

The formation of Yb-123 has been studied at different temperatures in air and in reduced oxygen partial pressure. It is found that the stability and/or the formation kinetics of Yb-123 phase is a major hurdle in manufacturing phase-pure Yb-123 in air. However, under reduced oxygen partial pressure, Yb-123 forms rapidly and more than 90% phase-pure Yb-123 is achieved within three sintering steps. Rods made from this powder were melt-processed in air and showed a T-c of 90 K. Kinetic studies performed by interrupting the growth during the directional solidification of these rods revealed a growth mechanism similar to that of Y-123 and a maximum growth rate of 7.2 mm/h for a stable planar interface. EPMA of the interface showed the liquid to be rich in barium cuprates with a Ba:Cu ratio of 1.3.