Synthesis, Crystal Structure, and Electrochemical and Magnetic Study of New Iron (III) Hydroxyl-Phosphates, Isostructural with Lipscombite

Abstract

Two novel iron (III) hydroxyl phosphates, of general formula Fe2 - y □ y (PO4)(OH)3 - 3 y (H2O)3 y - 2 (y = 2/3 or 0.82; □ represents vacancy), have been synthesized by the solvothermal method. The Rietveld refinement of the crystal structure from the X-ray powder diffraction was performed in a tetragonal cell with space group I41/a md. The structure is isotypic with the mineral caminite Mg1.33[SO4(OH)0.66(H2O)0.33] and is closely related to the mixed-valence lipscombite Fe2 - y PO4(OH) (0≤ y ≤ 2/3). The interconnection of the chains of face-sharing iron octahedra forms the “rod-packing” structure. In Fe1.18(PO4)(OH)0.57(H2O)0.43 (y = 0.82), about 60% of the chain sites are occupied, whereas about 2/3 of the chain sites are occupied in Fe1.33(PO4)(OH) (y = 2/3). The partial occupancy of the Fe3+ sites allows the incorporation of other cations into the structure. When ZnCl2 and NiCl2 were added into the hydrothermal mix, iron was partially substituted by these metal ions, giving Fe4/3 - z M z □2/3(PO4)(OH)1 - z (H2O) z (M = Ni, Zn; z = 0.28 and 0.26 for Ni and Zn, respectively), and increasing the cation occupation of the chains to about 2/3. The protons of the hydroxyl groups in these compounds can be replaced by lithium ions with structure retention. Lithium can also be incorporated electrochemically into the lattice, and the disordered compounds are good candidates for the cathode for secondary lithium batteries. The compounds exhibit magnetic phase transitions in the temperature range 60 to 90 K; the transition temperature increases with the number of magnetic ions in the chains.

Materials Challenges Facing Electrical Energy Storage

“…18 Another approach to raising the energy stored is to synthesize compounds with a higher ratio of redox ion to phosphorus, thus reducing the amount of deadweight phosphate. Compounds such as lipscombite, Fe 1.3 PO 4 O(H,Li), show some promise, 19 but because they have Fe-O-Fe bonds, the discharge potential falls to around 3 V as a result of a lowering of the inductive effect found in the olivine structure. One way around this difficulty might be to use manganese in place of the iron, which might again give a 3.5-V cell but with increased capacity.…”

Doped Framework Iron Hydroxyl Phosphate as Photocatalyst for Hydrogen Production from Water/Methanol Mixtures

“…Figure 1 shows selected XRD patterns for some of FeP samples as well as the structure for these materials as reported in the literature [31] , [32] . [31] , [32] . Noteworthy is the fact the crystallinity of FeP is maintained with some minor variations in the peak intensity in the presence of the dopant elements.…”

“…Materials preparation: One-dimensional iron phosphate (FeP) was prepared as reported from Song [31] , [32] . Briefly, an aqueous solution of ferric chloride, phosphoric acid and ethylendiamine (FeCl3 0.005 mol : H3PO4 0.04 mol : NH2CH2CH2NH2 2.5 mL : H2O 35 mL) was placed into a Teflon-lined autoclave of 200 mL, using a filling factor of 75 %.…”

Reversible Li Insertion Studies on V4O3(PO4)3as High Energy Storage Material for Li-Ion Battery Applications

“…. [31][32][33][34][35] The orthorhombic phase V 4 O 3 (PO 4 ) 3 consists of infinite chains of face sharing VO 6 octahedra and PO 4 tetrahedra. The three dimensional structure is formed by perpendicular chains along a, b axis connected with common vertices of oxide ion and PO 4 tetrahedra (Figure 1b) …”