Mössbauer study of the low-temperature phase of magnetite

Abstract

The Mossbauer spectrum of the low temperature phase of Fe,O, is studied a t 4.2 and 78 K. The spectrum can be resolved in five sextets, one arising from the Fe3+ ions on the A-sites, two from the Fe3+ ions on B-sites, and two from Fe2+ ions on the B-sites. The data of quadrupole splitting and hyperfine fields are used to obtain the ground and excited electronic states of the Fez+ ions on the B-sites.Das MoDbauerspektrum der Tieftemperaturphase von Fe,O, wird bei 4,2 und 78 K untersucht. Das Spektrum 1aBt sich in fiinf Sextetts auflosen, eins, das von Fe3+-Ionen auf den A-Pliitzen herriihrt, zwei von den Fe3+-Ionen auf den B-Pliitzen und zwei von Fez+-Ionen auf den B-Pliitzen. Die Werte der Quadrupolaufspaltung und der Hyperfeinfelder werden benutzt, um den Grundzustand und die angeregten elektronischen Zustlnde der Fe2+-Ionen auf den B-PILtzen zu erhalten.

Phase transition in nanomagnetite

“…12,23 Below T V , the fit was made earlier by four components. 24 However, in most cases, the spectra were fitted by five components, 12,25 resulting in the best result. Nevertheless, even more, six and nine components were supposed, 26,27 but the exact reason for the existence of these components was not given.…”

“…This attribution is in agreement with those published. 12,25 The appearance of the five components, some with different electric quadrupole splitting values, can be attributed to a complex monoclinic symmetry resulting in an electric field gradient at the cation sites in different sublattices. According to the refined model, the monoclinic cell has an orthorombic Pmca pseudosymmetry, constraining the atomic positions.…”

Synthesis of Improved Catalytic Materials for High-Temperature Water-gas Shift Reaction

“…[6][7][8][9] Magnetite (Fe3O4) and substituted magnetite-type ferrites -Me0.5Fe2.5O4 (Me = Mn 2+ , Co 2+ , Cu 2+ , etc.) are members of solid solution series, which permits the synthesis of samples with various magnetic properties and various degree of electron T delocalization.…”

“…It was found that the properties of nanosized spinel ferrites differ strongly from those of the corresponding bulk materials. [6][7][8][9] It was found that partially substituted magnetites (MexFe3-xO4) have better catalytic behavior than the MeFe2O4. [2][3] Up today, much attention has been paid to the preparation of such nanocrystalline bulk and supported materials, because of difficulty of their synthesis procedures and special techniques used.…”

“…Various synthetic methods have been developed to synthesize oxide nanoparticles, among them co-precipitation, thermal decomposition, sol-gel, microemulsion and other techniques. [2][3][6][7][8][9] It was established that the degree of crystallinity, particle size and particle morphology of oxide nanoparticles are strongly dependent on the method used for their preparation. In this regard the heterogeneous catalyst for water-gas shift reaction should have a number of characteristics.…”