Chemistry Reference
In-Depth Information
Rationalization of the Substructures Derived
from the Three Fluorite-Related [Li
6
(M
V
Li)N
4
]
Polymorphs: An Analysis in Terms
of the “Barnighausen Trees” and of the
“Extended Zintl-Klemm Concept”
D.J.M. Bevan, R.L. Martin, and
´
ngel Vegas
Abstract The crystallographic, group and subgroup relationships are explored for
mixed transition metal nitrides of the type: Li
7
M
V
N
4
. The hypot
h
etical parent
M
8
N
4
should have the anti-fluorite structure with the space group
m
3
m
. However,
the corresponding mixed-cation nitride [Li
7
V]N
4
is actually tri-morphic comprisin
g
one tetrag
on
al phase SG:
F
P
4
2
/
nmc
(
a
) and two cubic phases with space groups:
P
a
3
(
), respectively. These three polymorphs are clearl
y
subgroups
arising from lowering of symmetry of the parent space group,
b
) and
P
43
n
(
g
F
m
3
m
. Further
decomposition of the pathways (or B
arnighausen Trees) reveals a rich variety of
compounds derived from the subgroups and supergroups of the anti-fluorite parent
structure. The most important outcom
e
is that all the structures analysed in this
work, which derive from the parent F
m
3
m
space group of fluorite, can be identified
as partial substructures in the three phases of Li
7
VN
4
. All these substructures can be
rationalized as pseudo-compounds by assuming the appropriate electron transfer
between the atoms forming the nitride, following the extended Zintl-Klemm
concept (
EZKC
) that implies charge transfer between atoms, even if they are of
the same kind.
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