Stoichiometry of tetragonal and hexagonal Fe x Se: phase relations

Precise compositional analyses at spatial resolution 690 oC with annealing at 420 oC for ~24 hours. We define a modified phase diagram that includes this two phase field with β-FexSe and δ-FexSe for 1.02 < x < 0.90 and a second two phase field with β-FexSe and α-Fe for 1.08 < x < 1.02. This revised phase diagram for Fe:Se ~1.0 suggests that the peretectic transition nominally identified at x = 1.04 is not evident.