Journal of Crystal Growth, Vol.231, No.4, 568-576, 2001
Containerless solidification of oxide material using an electrostatic levitation furnace in microgravity
Containerless solidification of BiFeO3 has been carried out in microgravity with an electrostatic levitation furnace (ELF) on board a sounding rocket (TR-IA). This was the first time the ELF was used in microgravity to study the solidification behavior of oxide insulator material. A spherical BiFeO3 specimen with a diameter of 5 mm was laser heated and solidified in an oxygen and nitrogen mixture atmosphere. The microstructure resulting from solidification in the ELF was compared with that obtained from solidification in a 10 m drop tube and in crucibles. In the crucible experiments, the segregation of the primary Fe2O3 phase could not be suppressed, even if the cooling speed increased to 5000 K/s. However it did suppress in a 0.3 mm diameter droplet solidified in the drop tube experiment. This suggests that containerless processing effectively promoted the undercooling of the BiFeO3 phase. In the microgravity experiment, although a homogeneous BiFeO3 phase was not observed in the 5 mm spherical specimen, an anomalous fine cellular microstructure appeared due to high undercooling. In addition, the phase transitions of BiFeO3 were measured by DTA from room temperature to 1523 K and its liquidus temperature was estimated to be 1423 K.
Keywords:crystal morphology;solidification;microgravity conditions;oxides;perovskites;ferroelectric materials