On the miscibility gap of spinels MnxFe3−xO4+γ

Magnetic hausmannite from hydrothermally altered manganese ore in the Palaeoproterozoic Kalahari manganese deposit, Transvaal Supergroup, South Africa

“…R reaches a minimum value of 0.89 in the magnetic hausmannite (12 wt.% Fe203). This is considerably lower than R = 0.93 (or 6.9 wt.% Fe203) envisaged by Mason (1943), Van Hook and Keitb (1958), Halba et al (1973), and Osawa et al (1992 as the room temperature stability limit for the solubility of iron in the hausmannite lattice in the system Mn304-MnFe204. The composition reported for the magnetic hausmannite falls, according to all these studies, into the two-phase region, the single phase 'magnetic hausmannite' should therefore be unstable.…”

On the History and Recent Applications of Hyperfree Energy Describing Thermodynamics of Mobile Components in Partly Open Ceramic Systems

“…In 1970s the study of equilibria of oxides with atmosphere was also stimulated by the industry´s interest in the production of new ceramic materials (e.g., ferrites [1,26]) of required properties using an adequate high-temperature preparation procedure. Consequently, a new thermodynamic school developed in cooperation between the Czech Institute of Physics and the University of Chemistry and Technology (former Institutre of Chemical Technology) hindered at that time by political repressions [53] revealed in 1990´s [14][15][16] and successively continued through the studies of oxide high-temperature superconductors [3][4][5][6][7] and followed by others (e.g.…”

“…most recently cobaltites [9][10][11] prominent for their thermoelectric properties). However, in spite of so much work, which was concentrated on these systems of variable solid-gas interaction [1][2][3][4][5][6][7][8][9][10][11] no adequate thermodynamic resolution towards the partly open systems became accessible so that the case of related hyperfree energy is worth of more detailed presentation.…”

“…The recently emerging subject of oxides with variable stoichiometry including their phase equilibria with environment affected the novel field of thermodynamics of nonstoichiometric solids. This field has been promoted by Czech studies, the typical cases of which are represented by either spinels [1,2], superconductors [3][4][5][6], magnetoresistance manganites [7,8] or thermoelectric cobaltites [9][10][11] which required a novel approach for treating the interaction between a ceramic material and atmospheric oxygen. It is worth noting that the core of the associated innovative thermodynamic approach was laid by Czech chemist Pavel Holba [12][13][14][15][16] as a continuation of the respected Czech thermodynamic school commenced by Šatava [17,18] whose international impact is worth of a more detailed analysis.…”

Iron Manganites Synthesis by the Soft Chemistry Method

“…The phase diagram of the Fe/Mn/O system [5] shows that the spinel phase can be obtained in air at temperature above 950'C. Only a few works have been published on the synthesis of this stoechiometric spinel at low temperature [3,6,7]. Probably, the difficulty to obtain the stoechiometric spinel at low temperature is due to, the need of a better control of the reduction atmosphere, the weak crystallinity of the samples and the immiscibility gap described by Masson [8] for the natural "wredenburgite".…”