STRUCTURAL ASPECTS OF THE ALPHA-TRANSITION IN STOICHIOMETRIC FES - IDENTIFICATION OF THE HIGH-TEMPERATURE PHASE

Compounds of the Fe1-xS system ((0 ≤ x ≤ 0.125) are of NiAs type (a andc being the substructure lattice constants). For0 ≤ x ≤ 0.05, the temperature-induced metal-nonmetal α transition is associated with a structural change. Powder studies identify the influence ofx on the transition and especially on the superstructure reflection intensities of the hexagonal√3a,2c low-temperature (T < Tα) phase. Crystal growth for compositions in the transition range is detailed. The structural study of a stoichiometric FeS crystal at various temperatures gives evidence for disorder phenomena in the pretransition range and for the exact nature of the hexagonal HT phase(T > Tα) 2a,c (SGP63mc). Its structure refinement (R = 6.0%) rules out the previous tritwinned model ofMnP type. The cationic lattice of this2a,c modification is intermediate between the lattices of the LT√3a,2c phase and those of a pure NiAs phase. © 1990 Academic Press, Inc.