Rationalization of the Substructures Derived from the Three Fluorite-Related [Li6(MVLi)N4] Polymorphs: An Analysis in Terms of the “Barnighausen Trees” and of the “Extended Zintl–Klemm Concept” - Inorganic 3D Structures - page 126

Fig. 21 (a) The -Li 7 VN 4 structure viewed near [001]. V atoms - red, Li(1) atoms - green, Li(2)

atoms - yellow, Li(3) atoms - light blue, large to indicate that these are missing in the analogue
structure of Li 6 MoN 4 , N atoms - blue. (b) The Li 6 MoN 4 structure. Mo atoms - red, Li(1) atoms -
green, Li(2) atoms - yellow, N atoms - blue. Li(3) atoms are missing

a

Fig. 22 (a) Tetragonal zirconia: Zr atoms - red , O atoms - blue .(b) a -Li 7 VN 4 :Li(2)N 4 tetrahedra -
blue ,VN 4 tetrahedra - red

5.2 Tetragonal Zirconia

Further search for substructures in this same space group yielded the well-known
tetragonal zirconia structure [ 55 ]. In this structure, the Zr atoms are in site 2 b and
the O atoms in site 4 d , corresponding to the sites of Li(2) and V, respectively, in
a

-Li 7 VN 4 . However, there is almost a factor of four between the volumes of

a -Li 7 VN 4 and tetragonal zirconia; so once again we have a correspondence

between the two Zr atoms and the four O atoms of the zirconia structure [ 55 ] , on
one hand, and the two VN 4 tetrahedra and the four Li(2)N 4 of

a -Li 7 VN 4 , on the

other hand. This is shown in Fig. 22a, b .
If we consider the Nb analogue of -Li 7 VN 4 , viz .Li 7 NbN 4 , 3 Li atoms can donate

an electron to 3 N atoms, converting these to 3

a

-O atoms, while the Nb atom can
donate an electron to the remaining N atom, giving a total of 4

C

C

-O atoms and a

C C

single -Zr atom: in other words, the pseudo-compound Li-stuffed -[ZrO 2 ].