Formation of LuFe2O4 phase from an undercooled LuFeO3 melt in reduced oxygen partial pressure

Abstract

The formation of metastable phases from an undercooled LuFeO3 melt was investigated under reduced Po2 since the iron ion has the tendency to change its valence state from Fe3+ to Fe2+ in an ambient atmosphere with low Po2. The nucleation and the post-recalescence temperatures of the phases were decreased with decreasing process Po2. Phase equilibrium was established in the Lu–Fe–O system at 1473 K by varying the oxygen partial pressure from 105 to 10−1 Pa. A possible ternary metastable phase diagram depending on the oxygen composition in the bulk sample was also constructed. The formation of the LuFe2O4 phase where the Fe3+ and Fe2+ ratio is 1:1 clearly indicated that the formation of metastable phases is related to the presence of Fe2+ ions. Thermogravimetric analysis revealed that the increase in sample mass with decreasing process Po2, down to 10−1 Pa, is relatively dependent on the amount of Fe2+ ions.