Chemistry Reference
In-Depth Information
a
b
c
d
e
f
Fig. 8 (a) Perspective view of the triphylite FeLiP subnet, showing the Li layers intercalated
between the four-connected FeP network. (b) The Li layers showing the rectangular nets compa-
rable to those existing in
hcp
-Li and
fcc
-Li. (c) The delithiated Fe[PO
4
] structure, projected on the
ab plane. The O atoms are represented with
dark yellow spheres
. The Fe and P atoms are
represented as in (a). (d) The same structure without the O atoms to show clearly its similarity
with the FeS structure represented in (e) where the four connectivity is made evident. (f) The
structure of the NaAlSi Zintl phase showing the PbO-like structure of the [AlSi]
polyanion
This recurrent framework could be, in principle, associated with the fact that in
the Li-free compound, the FeP subnet corresponds to a (III)-(V) compound.
Remember that the same skeleton is found in the Zintl phase NaAlSi [
28
], where
the [AlSi]
Zintl polyanion, the (IV)-(IV)
C
-Si array, is forming the same frame-
work as represented in Fig.
8f
. Equivalent isostructural oxides, constituted by either,
(III)-(V) or (II)-(VI) cation arrays, are In[PO
4
], Ti[PO
4
], Cr[PO
4
] and Mn[SO
4
],
among others.
account for the observed structure in the delithiated Fe[PO
4
] phase. Thus, the Li
extraction takes place through a redox process where the Li
+
cations are reduced at
expenses of the oxidation of Fe
2+
to Fe
3+
. This means that the oxidized [Fe
III
P]
subnet becomes isoelectronic with MnS, and hence the iron phosphide could be
formulated as
-MnS. Consequently, Fe[PO
4
], isoelectronic to Mn[SO
4
], could
also be formulated as
C
-Mn[SO
4
], in view of the fact that the room temperature
The above interpretation can be correlated with the fact that the sulphide MnS
undergoes the NaCl
C
suggested on the basis of theoretical calculations [
32
] that this transition could
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