Binary alloys of the FeSex system have been prepared with x possessing the values 1.00, 1.04, 1.08, 1.12, 1.16, 1.25, 1.50, 1.75, and 2.00. Mössbauer spectra at room temperature have been taken for all and at liquid nitrogen temperature for some of them. The effect of thermal treatment is also investigated. The spectra are mostly quadrupole split or single lines, except for the compositions FeSe1.08 to FeSe1.16, which show magnetic hyperfine splitting. The iron ion exists in the high spin 2+ state for the entire system, with varying degrees of covalency.

Binary compounds FeTex have been prepared with x possessing the values 0.95, 1.2, and 2.0. They crystallise in the tetragonal α, hexagonal δ, and orthorhombic β phases, respectively. Mössbauer spectra are recorded for the three compositions from liquid nitrogen temperature to about 700 K. At room temperature and below, all of them exhibit quadrupole split spectra, and are characteristic of high spin Fe2+ covalently bound to the tellurium atom. At about 420 K, the spectrum of FeTe0.95 collapses into a single line. There is also a large change in the isomer shift versus the 1000/T curve at this temperature. The change is correlated to a variation in the conductivity curve also around this temperature region. Conversion of Fe2+ to Fe3+ explains the above phenomena. Similar changes in the isomer shift are observed at temperatures of 500 and 520 K, and accounted for in the case of FeTe1.2 and FeTe2.0, respectively.

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