Mössbauer studies on the FeTe system

Abstract

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.

Mössbauer spectroscopy evidence of intrinsic non‐stoichiometry in iron telluride single crystals

“…It is worthy to note that even a small amount of excess iron atoms leads to modification of the electronic properties of the Fe‐Te layers in Fe 1.05 Te. Moreover, we have shown that differentiation of the iron atoms into four groups is a reason for the asymmetry of the Mössbauer spectra for powdered samples of Fe(SeTe x ) compounds, reported in previous papers . We presume that our results could be extended on the entire class of FeSeTe x compounds which contain excess iron atoms.…”

“…Observation of the fine structure of the Mössbauer spectra complemented by ab initio calculations of the electric field gradients (EFG) on iron nuclei allows establishing a statistical distribution of excess iron atoms over the FeTe lattice. We argue that unexpected asymmetry of Mössbauer spectra reported in numerous papers for powdered samples can be attributed to over‐stoichiometric iron atoms and their influence on the regular iron atoms in the Fe(SeTe x ) type compounds.…”

“…In a number of papers an asymmetry of Mössbauer spectra of Fe(SeTe x ) powder samples was reported while the spectra are expected to be symmetric doublets. Indeed, FeSe which has crystal structure similar to FeTe, can be prepared as stoichiometric compound , i.e .…”

A 57Fe Mössbauer study of FeTe1−xSx

“…Probably, there is a certain amount of FeS hidden inside the FeTe structure invisible in the XRD characterization. FeTe 2 is paramagnetic down to 77 K [4,5]. It has an internal field which is less than 30 T. The magnetic component C 2 may be attributed to FeTe or FeTe 1Àx S x with low sulphur content.…”

“…The FeTe x system with different values of x has been studied a lot [4]. It exhibits various structures depending on the Fe-Te ratio [4][5][6]. An iron excess causes structural transformation.…”