Impact of lithium and potassium cations on the Mössbauer spectral and electrical properties of two mixed-valence iron(II/III) phosphites
Résumé
Based on the combined corrected chemical analysis, the single-crystal X-ray structural results, and the revised Mössbauer spectral analysis, the best formulation of Li1.4(1)[Fe4.4(1)IIFe0.6(1)III(HPO3)6]·1.47(3) H2O, 1b, has been obtained; also, from a revised Mössbauer spectral analysis, a revised formulation of K0.95(5)[Fe3.95(5)IIFe1.05(5)III(HPO3)6]·0.5 H2O, 2m, has been obtained. The revised analysis of the room-temperature Mössbauer spectral parameters for both compounds is consistent with their crystallographic structures and the different nature and occupancies of the Li+ and K+ crystallographic sites. From a detailed analysis of the impedance spectroscopy measurements of Li1.43[Fe4.43IIFe0.57III(HPO3)6]·1.5 H2O, 1, between 123 and 189 °C, two processes involving the electric charge response to the ac electric field have been identified. An activation energy for the charge transfer in 1 of 0.91(2) eV or 7340(160) cm–1 has been obtained; the charge transfer may involve a correlated hopping of the Li+ ion and an electron between the iron(II) and iron(III) ions.