Abstract 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 P 3 ‾ ↔ P 1 ‾ . 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.

中文翻译：

---

混合价水合氟钛酸铁：合成、光学和量热法

摘要 理想分子式为FeTiF6·6H2O的混合价水合氟钛酸盐是天然矿物钛铁矿用氢氟酸氟化处理的主要产物。其单晶生长并在 200-350 K 的温度范围内进行光学和量热实验。电荷重新分布，Fe2+Ti4+ 到 Fe3+Ti3+，在 XPS 光谱中很明显。一阶铁弹性相变发生在温度 T0↓ = 271.5 K，T0↑ = 274 ÷ 275.5 K 时，对称性变化 P 3 ↔ P 1 ‾。结构转变伴随着切片 (001) 中出现非常弱的光学各向异性、热容的小异常 (ΔS = 1.5 J/mol K = 0.2R) 和正压力系数 dT0/dp ≈ 30 ± 10 K/GPa。