In situ observation and simulation of growth process of faceted RE123 crystals

To clarify the growth mechanism of faceted REBa₂Cu ₃O_{7 δ} (RE123, RE = Sm, Y) crystals, the growth process of the crystals was observed in situ by using a high temperature microscope. The growth rate of each faceted interface of a crystal growing from the liquid + 211 phases under an undercooling was obtained from the relationship between the position of each interface and growth time. It was observed that some of the faceted interfaces of a growing crystal stopped growing after a period of time, while other interfaces continued to grow with a growth rate approximated by a function of the undercooling. The above stoppage of the growth was observed in situ for the first time, and this fact could give powerful support to the mechanism for a similar phenomenon in REBCO films which were fabricated by the trifluoroacetates metal organic deposition method: growing microstructures of RE123 crystals in the film were revealed by transmission electron microscopy (TEM) for quenched specimens. Some very thin a-axis grains were formed by a change in c-axis growth rate. Furthermore, we showed the above growth and stop phenomena of faceted interfaces of REBCO crystal grains using numerical simulations.