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Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO 3 Melt Using an Aerodynamic Levitator
Author(s) -
Vijaya Kumar Malahalli S.,
Kuribayashi Kazuhiko,
Kitazono Koichi
Publication year - 2009
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2009.02974.x
Subject(s) - partial pressure , orthorhombic crystal system , ionic radius , differential thermal analysis , analytical chemistry (journal) , materials science , annealing (glass) , thermogravimetric analysis , metastability , phase diagram , oxygen , atmospheric temperature range , ionic bonding , phase (matter) , crystal structure , thermodynamics , crystallography , chemistry , ion , diffraction , metallurgy , physics , organic chemistry , chromatography , optics
The Yb 2 O 3 –Fe 2 O 3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 10 5 to 10 −1 Pa. Two kinds of metastable phases, with space groups of P 6 3 cm and P 6 3 / mmc , were found through rapid solidification of an undercooled YbFeO 3 melt in an atmosphere with reduced P o 2 . The crystal structure of the as‐solidified samples changed from orthorhombic Pbnm to hexagonal P 6 3 cm and P 6 3 / mmc with decreasing P o 2 . X‐ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as‐solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric–differential thermal analysis (TG‐DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb–Fe–O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe 2+ , which has an ionic radius larger than that of Fe 3+ , decreases the tolerance factor and therefore destabilizes the perovskite structure.