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take place through an intermediate PbO-like phase. This intermediate phase, which
has ever been reported for the binary compound FeP, could be a metastable
arrangement stabilized in Fe[PO
4
] as a consequence of the role played by the O
atoms in forming high pressure phases of the alloys [
11
].
3 The High Pressure Phase
-FeLi[PO
4
]
b
In this section, we will describe the structure of
-FeLi[PO
4
], synthesized at
high temperature and pressure [
2
]. Two important structural features distinguish
this
b
-phase from the triphylite structure. The first one is a change in symmetry,
from the space group
b
P
nma of triphylite to the supergroup
C
mcm in the HP
phase
-FeLi[PO
4
]. The second one is that the Li and Fe atoms exchange their
position in the structure as it can be observed by comparing Fig.
9a
with both
b
a
b
c
d
Fig. 9 (a) The structure of the high pressure phase of
b
-FeLi[PO
4
](Cmcm) showing the exchange
of the Li and Fe atoms with respect to the olivine-like phase (Pnma) of triphylite (compare with
Fig.
2
).
Blue lines
highlight the trigonal prisms centred by the PO
4
groups. (b) The same structure
in which the
hcp
array of P atoms (
red-violet spheres
) has been depicted. All the octahedral holes
are occupied by the Fe atoms in contrast to the triphylite structure represented in Fig.
5a
.(c) The
structure of the Cmcm structure of FeSO
4
to show its similarity with that of Fe[PO
4
] subarray
represented in (b). (d) The structure of the orthorhombic phase of FeS (Cmcm), a distortion of the
NiAs type, to show its coincidence with both the Fe[PO
4
] subarray (b) and the Fe[SO
4
] structure
drawn in (c)
