Crystal structure and Mössbauer study of FeAl 2 O 4

Hercynite (FeAl2O4) is one of the endmembers of the spinel group minerals that have the general formula AB2O4. This formula describes the spinel compound with normal cation distribution which means that all the divalent cations occupy tetrahedral sites (Td), whereas all the trivalent cations are located in the octahedral environment (Oh) [1]. However, the intersite exchange of the cations is possible, for example hercynite crystal lattice commonly contains Fe3+ cations in the Oh sites as a result of the formation process [2–4]. Furthermore, Al3+ ion occurrence in Td sites is also feasible. This disordering process can be described by the formula (A1−xBx) (AxB2−x)O4, where x defi nes disorder degree and symbols IV and VI refer to Td and Oh coordination, respectively. When the x parameter takes a value of 0 spinel possesses a normal cation distribution while for x = 1 the distribution is fully inversed. Each spinel may be fully characterized by determination of three structural parameters a, u, and x, i.e. the lattice parameter, the oxygen positional parameter, and the cation inversion parameter, respectively. Iron-aluminate spinel, which is the concern of this work possesses regular symmetry and crystalizes in the space group Fd3m with the Fe2+ cation in site 8a (1/8 1/8 1/8), the Al3+ cations in site 16d (1/2 1/2 1/2), and the anions O2− in site 32e (u u u) [4]. The aim of this study was to characterize hercynite synthesized by the non-traditional arc-melting method by means of the crystal structure determination, together with the local chemical environment and charge of iron in this spinel. Crystal structure and Mössbauer study of FeAl2O4 Ilona Jastrzębska, Jacek Szczerba, Paweł Stoch, Artur Błachowski, Krzysztof Ruebenbauer, Ryszard Prorok, Edyta Śnieżek