Phase Selection in the Undercooled Melts of RMnO3 (R=rare earth) Using Containerless Solidification Technique

Int. J. Microgravity Sci. Appl. 2011_s051
The low oxygen partial pressure Po2 of an ambient atmosphere is considerably effective for phase selection in the RMnO3 system, since the Mn ion changes its valence states depending on Po2. Containerless solidification of the undercooled RMnO3 melt was carried out to study phase formation behavior under precisely controlled Po2. The orthorhombic and hexagonal RMnO3 phases were solidified from an undercooled melt at Po2=105 Pa. X-ray diffraction patterns and cross-sectioned microstructure revealed the existence of orthorhombic and hexagonal RMnO3. Thermodynamic stabilities were studied at various temperatures. The oxygen deficiencies in the as-solidified samples were calculated through annealing at 105 Pa using TG-DTA. These results suggest that the containerless solidification is one of the most suitable methods for phase equilibrium study under controlled Po2.

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