Mössbauer-Effect Study of Calciomagnetites

Abstract

Cax Fe3-x O4 samples, with x _ < 0.28, prepared from α-Fe 2 O 3 and CaO by the Bridgman method were investigated by means of 57 Fe Mossbauer spectroscopy. Room temperature spectra gave evidence that the samples were multiphase, the calciómagnetite being the dominant phase with a contribution of 73% to 99%, depending on the sample. Analysis of the subspectra associated with the calciomagnetite gave evidence that Ca-ions reside on the tetrahedral (A) sites and have not random distribution. Their presence on those sites causes a reduction of the hyperfine field at Fe nuclei occupying the octahedral positions (B) by 12.3(1.0) kOe per one Ca-ion and a decrease in the average hf field, (ΗB)/dx, at the rate of 29 kOe/mol% for x < 0.07 and of 387 kOe/mol% for larger x. In addition, a linear correlation between (ΗB) and the average isomer shift, (IB), was revealed to hold. It indicates that addition of Ca-ions into the magnetite causes a decrease in the spin-density and an increase in the charge-density at Fe nuclei occupying the B-sites.

Distribution of Cr atoms in the surface zone of Fe-rich Fe–Cr alloys quenched into various media: Mössbauer spectroscopic study

“…Noteworthy, this way of the spectra analysis measured on various binary alloys of Fe has become a standard. In the case of the Fe-Cr alloys it was successfully applied even for the alloy with 45.5 at.% Cr [36], yielding B 1 = -32.5 kGs and B 2 = -20.5 kGs in a very good agreement with the corresponding values found by the analysis of much less concentrated spectra [33,34,[37][38][39][40].…”

“…The position of the minimum in <B> coincided with the composition where the SG phase occurs. According to the author's interpretation, these values reflect localized changes in the Fe-site spin-density whereas the Cr concentration change in B similar for the three configurations was interpreted as due to the change in the polarization of the conduction electrons, hence in the B CEP term of the hyperfine field [37]. Noteworthy, the interpretation of the latter was confirmed by performing measurements at 119 Sn diffused into the matrices of the Fe-Cr alloys.…”

“…The dashed line is the best-fit of the 57 Fe data to a quadratic equation. The plot was made using the data from [37,122].…”

Debye temperature of disordered bcc-Fe–Cr alloys

“…For the present study our previously fabricated microcrystalline samples of Fe-Cr alloys [15,16] as well as some new, and similarly prepared, ones were used. The Cr-rich alloys were made with iron in the form of a ∼95%-enriched 57 Fe isotope in order to record good quality spectra in a reasonable time.…”

Chemical, physical, structural and morphological characterization of the electric arc furnace dust

“…Such a behavior is due to the fact that calcium substitutes iron randomly at the site B, occupying in a disordered way the iron place in the magnetite B site. The result is that, for each unit-cell, there are different hyperfine interactions and, consequently, a hyperfine magnetic field distribution in this site [21].…”