Details

Autor(en) / Beteiligte

• Mel'nikova, Svetlana V.
• Laptash, Natalia M.
• Gorev, Mikhail V.
• Pogoreltsev, Evgeniy I.

Titel

Mixed-valence hydrated iron fluoridotitanate: Synthesis, optics and calorimetry

Ist Teil von

• The Journal of physics and chemistry of solids, 2020-07, Vol.142, p.109444, Article 109444

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2020

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• Mixed-valence hydrated fluoridotitanate with idealized formula FeTiF6·6H2O is the main product of fluoride processing of natural mineral ilmenite with hydrofluoric acid. Its single crystals were grown and optical and calorimetric experiments were carried out in the temperature range 200–350 K. Charge re-distribution, Fe2+Ti4+ to Fe3+Ti3+, in the compound studied was evident in XPS spectra. A first order ferroelastic phase transition occurs at temperatures T0↓ = 271.5 K, T0↑ = 274 ÷ 275.5 K with the symmetry change P3‾↔ P1‾. The structural transformation is accompanied by the appearance of a very weak optical anisotropy in the slice (001), a small anomaly of the heat capacity (ΔS = 1.5 J/mol K = 0.2R), and positive baric coefficients dT0/dp ≈ 30 ± 10 K/GPa. •High quality mixed-valence single crystals of hydrated iron hexafluoridotitanate were obtained.•Calorimetric experiments revealed first order phase transition at 271.5–275.5 K.•Optical studies confirmed the presence of a ferroelastic phase transition from trigonal to triclinic syngony.•This transformation is accompanied by the appearance of a weak optical anisotropy and a small anomaly of the heat capacity.