In situ observation and analysis of crystal growth process of GdBCO superconductive oxide

To clarify the nucleation and growth process of 123 crystals, growth of faceted Gd123(GdBa2Cu3O7−δ) crystals was observed in situ on MgO(1 0 0) by using a high temperature optical microscope with zoom lens (×50-500). Gd123 crystals nucleated and grew at each undercooling (ΔT = 30, 35, 40, 45 K). Growth rate (u) and incubation time (tinc) for nucleation were obtained from the relationship between time and position of faceted interface. u was approximated by a function of ΔT: u=AgpΔTr2/η(T), where Agp is a constant, Agp = 1.0 × 10−5. Nucleation rate (Iv) was obtained from the relationship between time and number of nucleated crystals. Iv was approximated by an exponential function: Iv={An/η(T)}exp(-B/ΔTr2), where An and B are constants, An = 1.3 × 107, B = 2.7 × 10−3. The nucleation and growth process of Gd123 crystals were expressed quantitatively by the above equations.