In-situ observation and analysis of crystal growth process in NdBCO and SmBCO superconductive oxide

The growth process of RE123 (REBa ₂Cu ₃O _7-x, RE = Nd and Sm) crystals in the atmosphere of Ar-1%O ₂ were observed insitu to investigate the nucleation and growth process of faceted RE123 crystals from the liquid +422(Nd ₄Ba ₂Cu ₂O ₁₀) or 211 (Sm ₂BaCuO ₅) on MgO(100) substrate through a peritectic reaction by using high temperature optical microscope with zoom lens. The nucleated faceted 123 crystals grew at a rate depended on the undercooling (Δ T). Growth rate (u) and incubation time (t _inc) for nucleation were obtained from the changes in position of faceted interface during isothermal solidification. Growth rate u (m/s) was approximated by the following relation: u=A _g (Δ T _r ²/η (T) ), where η (T) was the viscosity, Δ T= T _p - T, Δ T _r=ΔT/ T _p, T was temperature, T _p was peritectic temperature, A _g was a constant: A _g = 0.60×10 ⁶ for Nd and A _g=1.8×10 ^-5 for Sm. Nucleation rate(I _v) was obtained from the relationship between the number of nucleated crystals(n) and time(t). I _v(m ^-3 s ^-1) was approximated by I _v= A _n(1/η(r)) exp (-B/ΔT _r ²), where A _n and 5 were constants: A _n = 3.5×10 ⁷, B= 1.5 ×10 ^-3 for Nd, and A _n = 12.5×10 ⁷, B=3.2×10 ^-3 for Sm.