The Phase Transformation in Ferreous Fluosilicate Hexahydrate

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Abstract
The structural change of FeSiF6, . 6 H2O at T, = 225 K (P21/C to P3ml above Te) is well known from X‐ray measurements. The temperature dependence of the Mössbauer parameters in the neighbourhood of the phase transformation (200 K ≦T≦ 250 K) is studied. At Te, the quadru‐pole splitting ΔEq changes with increasing temperature by (+0.009 ± 0.002) mm/s, the Lamb factor f slightly decreases by δf = −0.011 ±0.004, while the anisotropy of f changes remarkably: δ(f∥ ‐ f⊥) = −0.18. From the relaxation broadening of the absorption lines below and above Te, it is concluded that the non‐axial terms of the ligand field at the Fe2+ ion do not vanish above the transition temperature.