FeLi[PO4]: Dissection of a Crystal Structure - Inorganic 3D Structures - page 74

appears. If the Li atoms (grey spheres) are neglected, the remaining Fe and P atoms
form a four-connected skeleton of the PbO type which alternate with the Li layers
along the a axis. A perspective view of these blocks is represented in Fig. 6b . This
PbO-type structure is also adopted by III-V compounds such as InBi [ 23 ].
The goodness of this interpretation becomes evident by applying the EZKC. The
Li atom acts as donor, transferring its valence electron to the P atom which becomes
C -S]. The marvellous feature

is that this is the structure of one of the phases of real FeS itself! The Li atoms have
produced the conversion of the [FeP] subarray (Fe

-S, so that the [FeP] subarray can be formulated as [Fe C

-S) into a true FeS structure.
Another feature which must be remarked upon is that the FeLiP subarray of
triphylite (FeLi[PO 4 ]) adopts the same structure as the Zintl phase FeLiP [ 24 ] , in
which the [FeP] subarray is also of the PbO type. The three structures, i.e. FeLi
[PO 4 ][ 2 ] , FeLiP [ 24 ] and the HT phase of FeS [ 25 ], are shown in Fig. 7 for
comparison.
However, the most intriguing feature is how the FeS substructure is maintained
when we add the Li atoms in the Zintl phase FeLiP, and even when four additional
oxygens are inserted into the structure of the FeLi[PO 4 ] oxide (triphylite). It is
intriguing that such a structural motif remains when more and more atoms are
added to the structure. These compounds represent new examples of two general
trends observed in many oxides. On the one hand, their cation arrays maintain the
structures of their respective alloys [ 11 ] . On the other hand, the

C

ZKC can be

successfully applied to explain the cation arrays in oxides [ 4 ].

a b c

d

Fig. 7 (a) The cation array of FeLi[PO 4 ] (triphylite) showing its similarities with the structure of
the Zintl phase FeLiP, drawn in (b) and with the FeS structure which is of the PbO type (c). In (d),
we have separated one of the planar nets formed by the Li and P atoms in (b). They correspond to
{100} planes of the rocksalt LiCl