FeLi[PO4]: Dissection of a Crystal Structure - Inorganic 3D Structures - page 67

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
2 Description of the Triphylite FeLi[PO 4 ] Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2.1 Olivine FeLi[PO 4 ] and the Ni 2 In Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.2 FeLi[PO 4 ] and the AlB 2 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.3 The FeLiP Subarray and NiAs·FeLi[PO 4 ] and Li[ClO 4 ] ..............................72
2.4 FeLiP, and FeLi[PO 4 ]: The Extended Zintl-Klemm Concept . . . . . . . . . . . . . . . . . . . . . . . . 74
2.5 The Li Subarray and the Structures of Elemental Li . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3 The High Pressure Phase b -FeLi[PO 4 ] ..................................................... 78

3.1 Relationships of -FeLi[PO 4 ] with Fe[SO 4 ] and Li[ClO 4 ] ............................79

3.2 The Exchange of Li and Fe in the Transition Triphylite

b

-FeLi[PO 4 ] ............80
4 FeLi[PO 4 ] and the High Temperature Phases of Na 2 [SO 4 ] ................................ 80
4.1 FeLi[PO 4 ],

! b

-Fe[SO 4 ] in the Light of the EZKC . . . . . . . . . . . . . . . . . . . 81
4.2 The Olivine-Like Structures and the PbO-Type Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.3 The Co-existing Structures FeS/Fe[SO 4 ], LiCl/Li[ClO 4 ] and FeLiP/FeLi[PO 4 ] ......85
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

C -Mg[SO 4 ] and C

Daß hier ein gemeinsames Prinzip und kein Zufall herrscht, ist wegen der sehr starken
Analogie wahrscheinlich.
It is probable that this is not a casual coincidence but the strong analogies must obey a
General Principle.

Wondratschek, Merker & Schubert, 1964

1 Introduction

The compound FeLi[PO 4 ] is one of the many quaternary olivine-like compounds. In
common with many Li-containing oxides, it has been widely studied due to its
potential use as anode batteries. The compound is dimorphic. At ambient conditions,
the stable phase is the mineral triphylite whose structure was first determined by
Yakubovich et al. [ 1 ] . It is olivine-like (

nma) and hence, isostructural to forsterite,
Mg 2 [SiO 4 ], and more properly to sinhalite AlMg[BO 4 ](alsoCaMg[SiO 4 ]). At high
temperature and pressure (around 80 GPa and 1,100 K), a metastable

P

b -phase, with

the NaCaVO 4 -type structure ( mcm), was synthesized in a belt-type apparatus [ 2 ] .

The two phases of FeLi[PO 4 ] are isostructural with two high temperature phases
of Na 2 [SO 4 ] which are obtained when the room temperature phase, V-Na 2 [SO 4 ]
(the mineral thenardite), is heated. By increasing temperature, the observed transi-
tion sequence is thenardite V-(

C

! ! !

F ddd) III- C mcm II- P nma I- P 6 3 /mmc [ 3 ] .

Both, III-Na 2 [SO 4 ]( C mcm) (Na 2 [CrO 4 ] type) and II-Na 2 [SO 4 ]( P nma) (Mg 2 [SiO 4 ]

type) are the phases related to those of FeLi[PO 4 ].
The three high temperature phases of Na 2 SO 4 ,i.e. 6 3 /mmc,

present strong topological similarities [ 3 , 4 ], and their cation arrays are all of the Ni 2 In
type [ 5 ] . In case of the two phases of FeLi[PO 4 ], the [FeLiP]-arrays can also be
considered of the Ni 2 In type, but the two phases (

C mcm, P nma and P

C mcm and P nma) differ in an