Phase Formation of YbBa2Cu4O8 Films in Metal–Organic Deposition Method

YbBa
₂
Cu
₄
O
₈
(Yb124) films were fabricated using metal-organic deposition method, and crystal growth of c-axis oriented films was discussed based on transmission electron microscopy (TEM) and X-ray diffraction. The c-axis oriented YbBa
₂
Cu
₃
O
_7-x
(Yb123) and Yb124 films were formed depending on annealing time and temperature. Yb123 grew in high temperature (800 °C-840 °C) even at short annealing time, but Yb124 was formed in lower temperature (760 °C-800 °C) at long annealing time. It is expected that the growth rate of Yb123 is larger than that of Yb124 due to the simple structure of Yb123. The phase diagram of Y-Ba-Cu-O indicates that Y123 is unstable in temperature lower than 750 °C, and Y124 and Y123 coexist in higher temperature. Assuming that the phase diagram is similar in Y-Ba-Cu-O and Yb-Ba-Cu-O, the present results are consistent with the phase diagram. Annealing time dependence of microstructure was evaluated for annealing temperature of 760 °C using TEM. The thickness of Yb124 increased with the increase in annealing time, and Yb124, which was transformed from Yb123, contained planar defects parallel to the c-axis. Yb124 grows without transforming to other phases, and metastable Yb123 transforms to Yb124 by forming the planar defects at the temperature where Yb124 is stable and Yb123 is unstable.