Four different hydrated iron phosphates were prepared as pure crystalline powders by precipitation in aqueous solutions under controlled pH: strengite, FePO₄·2H₂O (Pbca; a = 9.8923(6) Å, b = 10.125(1) Å, c = 8.729(1) Å); metastrengite I, FePO₄·2H₂O (Pbnm; a = 5.226(2) Å, b = 10.026(3) Å, c = 8.917(3) Å); metastrengite II, FePO₄·2H₂O (P2₁/n; a = 5.3276(3) Å, b = 9.800(1) Å, c = 8.7129(6) Å, β = 90.532(6)°); and spheniscidite, NH₄(Fe₂(PO₄)₂OH·H₂O)·H₂O (P2₁/n; a = 9.808(3) Å, b = 9.727(3) Å, c = 9.866(3) Å, β = 102.85(2)°). Thermogravimetric analysis revealed slightly more than 2 H₂O molecules per FePO₄ for the first three compounds, the excess being considered as adsorbed on the powders' surface. Temperature-controlled X-ray diffraction allowed isolation and determination of the stability domains of a large number of FePO₄ polymorphs which may, or may not, reabsorb H₂O upon exposure to ambient air. All these phases, after careful optimization of the electrode preparation, may be reversibly reduced to ∼90% of their theoretical capacities within the 2−4 V vs Li⁺/Li region.

中文翻译：

---

锂电池中作为目标的结晶水合磷酸铁（III）的合成及热行为

通过在受控pH值下在水溶液中沉淀制备四种不同的水合磷酸铁盐，使其成为纯净的结晶粉末：硬石粉，FePO ₄ ·2H ₂ O（Pbca ; a = 9.8923（6）Å，b = 10.125（1）Å，c = 8.729 （1）Å）; 变质子I，FePO ₄ ·2H ₂ O（Pbnm ; a = 5.226（2）Å，b = 10.026（3）Å，c = 8.917（3）Å）; 变硬石II，FePO ₄ ·2H ₂ O（P 2 ₁ / n ; a = 5.3276（3）Å，b= 9.800（1）Å，c = 8.7129（6）Å，β= 90.532（6）°）; 以及绿闪石，NH ₄（Fe ₂（PO ₄）₂ OH·H ₂ O）·H ₂ O（P 2 ₁ / n ; a = 9.808（3）Å，b = 9.727（3）Å，c = 9.866（ 3）Å，β= 102.85（2）°）。热重分析表明，每个FePO ₄略多于2个H ₂ O分子对于前三种化合物，过量被认为是吸附在粉末表面上。大量的FePO的稳定结构域的温度控制的X射线衍射允许隔离和确定₄多晶型物，其可以或可以不重新吸收ħ ₂ ö在暴露于环境空气。在精心优化电极制备后，所有这些相都可以在2-4 V vs Li ⁺ / Li区域内可逆地降低至其理论容量的〜90％。