Synthesis, crystal structure and lithium motion of Li8SeN 2 and Li8TeN2

Article abstract of DOI:10.1002/zaac.201000002

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess lithium. The crystal structures were refined using single-crystal X-ray diffraction as well as X-ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) A, c = 9.995(1) A, Te: a = 7.217(1) A, c= 10.284(1) A). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and lithium distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X-ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of lithium atoms in the title compounds were revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Lithium motion starts for Li₈SeN₂ above 150 K whereas it is already present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR spectroscopic parameters reveal clearly different environments of the lithium atoms determined by the electric field gradient, which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of lithium predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.

Full text of DOI:10.1002/zaac.201000002

ARTICLE
DOI: 10.1002/zaac.201000002
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
8
2
8
2
[
a]
[b]
[c]
[d]
Daniel Bräunling, Oliver Pecher, Dmytro M. Trots, Anatoliy Senyshyn,
[e]
[f]
[g]
Dmitry A. Zherebtsov, Frank Haarmann, and Rainer Niewa*
Dedicated to Professor Rüdiger Kniep on the Occasion of His 65th Birthday
Keywords: Lithium; Nitrides; Chalcogenides; Li motional processes; Solid state NMR spectroscopy; Quantum mechanical calculations
Abstract. The compounds Li
form of orange microcrystalline powders from reactions of Li
Li N. Single crystal growth of Li SeN
excess lithium. The crystal structures were refined using single-crystal
X-ray diffraction as well as X-ray and neutron powder diffraction data
8 2
EN with E = Se, Te were obtained in compounds were revealed by temperature dependent NMR spectro-
2
E with scopic investigations. Those are indicated by significant changes of the
7
3
8
2
additionally succeeded from
8
Li NMR signals. Lithium motion starts for Li SeN2 above 150 K
8 2
whereas it is already present in Li TeN at this temperature. Quantum
mechanical calculations of NMR spectroscopic parameters reveal
clearly different environments of the lithium atoms determined by the
electric field gradient, which are sensitive to the anisotropy of charge
distribution at the nuclear sites. With respect to an increasing coordina-
tion number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2),
and Li(1), respectively, the values of the electric field gradients de-
I4
1
( md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a =
7
.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes
with an anionic substructure motif known from cubic Laves phases and
lithium distributed over four crystallographic sites in the void space of
the anionic framework. Neutron powder diffraction pattern recorded in
the temperature range from 3 K to 300 K and X-ray diffraction patterns
using synchrotron radiation taken from 300 K to 1000 K reveal the
crease. Different environments of lithium predicted by quantum me-
7
structural stability of both compounds in the studied temperature range chanical calculations are confirmed by Li NMR frequency sweep ex-
until decomposition. Motional processes of lithium atoms in the title periments at low temperatures.
Introduction
Lithium nitride halides are already well investigated, with
emphasis on phase formation, crystal structures and lithium ion
mobility. Early investigations originated from Sattlegger and
Hahn in the 1960s [1, 2]. In the meantime the compounds have
attracted some attention as fast solid lithium ion conductors
[3–6]. More recent investigations in these systems elucidate
structures and structural relationships of compounds that can
be described with the general composition Li3–2yN1–yXy with
X = Cl, Br, I [7–15]. In general, the crystal structures can be
understood as products of acid-base reactions in which the
*
Prof. Dr. R. Niewa
Fax: +49-711-685-64241
E-Mail: rainer.niewa@iac.uni-stuttgart.de
[
a] Department Chemie
Technische Universität München
Lichtenbergstraße 4
framework structure of α-Li N [16] is broken down to units of
3
85747 Garching, Germany
lower dimensionality. In comparison to the investigations on
lithium nitride halides, the data on lithium nitride chalcogen-
ides are extremely rare [17, 18]. Here we present crystal struc-
[
b] Max-Planck-Institut für Chemische Physik fester Stoffe
Nöthnitzer Straße 40
01187 Dresden, Germany
[
c] Bayerisches Geoinstitut
Universität Bayreuth
Universitätsstraße 30
ture analysis and thermal expansion for Li SeN and Li TeN
8
2
8
2
in a wide range of temperatures obtained from X-ray, synchro-
tron radiation and neutron diffraction data. Additionally, we
used solid state NMR spectroscopy to probe motional proc-
esses of lithium atoms. Furthermore, the lithium bonding situa-
tion was investigated by combined application of quantum me-
chanical calculations and NMR spectroscopic experiments.
95447 Bayreuth, Germany
[
d] Fachbereich Material und Geowissenschaften
Technische Universität Darmstadt
Petersenstraße 23
64287 Darmstadt, Germany
[
e] South Ural State University
Prospect Lenina 76
Chelyabinsk 454080, Russia
f] Institut für Anorganische Chemie
RWTH Aachen
[
Results and Discussion
Synthesis and Composition Determination
Landoltweg 1
52074 Aachen, Germany
[
g] Institut für Anorganische Chemie
Universität Stuttgart
Pfaffenwaldring 55
To derive optimal reaction temperatures for the preparation
of the title compounds Li SeN and Li TeN we first carried
70569 Stuttgart, Germany
8
2
8
2
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201000002 or from the
author.
out several DTA measurements (Figure 1). The reaction of
lithium with appropriate amounts of selenium or tellurium for
9
36
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 636, 936–946

8 2 8 2
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
the formation of Li E (E = Se, Te) in an argon atmosphere tion. The products were microcrystalline orange powders with
2
results in strongly exothermic reactions at 490 K and 691 K, a slightly darker color for the tellurium compound. Chemical
respectively. The reactions proceed well above the melting analyses of the obtained powder samples revealed very minor
point of pure lithium, which can be taken from the measure- impurities of oxygen and resulted in the following composi-
ments as endothermic effect at about 450 K. The onset-temper- tions: Li7.90(6)Se1.00(1)N2.05(6)O0.025(1) (w(Li) = 33.60 ± 0.24 %,
ature for the formation of Li Se coincides with the melting w(Se) = 48.41 ± 0.25 %, w(N) = 17.62 ± 0.51 %, w(O) = 0.25
2
point of selenium (494 K), whereas the reaction with tellurium ± 0.01 %) and Li8.03(6)Te1.00(1)N2.18(4)O0.0017(4) (w(Li) = 24.94 ±
initiates some 30 K below the respective melting point of tellu- 0.18 %, w(Te) = 57.07 ± 0.61 %, w(N) = 13.66 ± 0.25 %,
rium (723 K), corresponding to the formation of the eutectic w(O) = 0.12 ± 0.03 %). Under the identical preparation condi-
melting temperature LiTe –Te (696 K). In comparison, the tions, but with an excess of lithium single crystals of Li SeN2
3
8
phase diagram of Li–Se does not contain any eutectic with were obtained.
lower melting point than pure selenium [19]. In both cases the
reaction starts with a very sharp edge in the DTA-peak with
Crystal Chemistry
no indication of a partial melting of selenium or the tellurium
containing eutectic, respectively, which should add some endo-
For crystal structure refinements in-house X-ray powder pat-
thermic contribution. In a second series of experiments appro- terns were indexed with tetragonal unit cells of a = 7.060(2) Å,
3
priate molar ratios of Li N were added to the mixtures of lith- c = 9.9689(7) Å, V = 496.85(9) Å (Se), a = 7.2127(3) Å, c =
3
3
ium and E. The resulting DTA curve for E = Se shows an 10.2793(4) Å, V = 534.76(2) Å (Te). At this point it is worth-
exothermic chemical reaction starting even slightly below the while to point out that those cells are metrically quite close to
melting point of pure lithium and smeared out over a much cubic, particularly for Li SeN , however, the reflection split-
8
2
broader temperature range. For E = Te the reaction starts at a ting can be clearly observed on close inspection. We note, that
slightly higher temperature than observed for the binary case, a similar cubic unit cell was reported for Li IN [2]. The struc-
7
2
¯
but is similarly smeared out to higher temperatures. Since the ture of this iodide was described in space group F43m with a
reaction products contained significant amounts of the binary highly disordered Li-substructure [15]. For the title compounds
compounds next to the ternary products the higher preparation an analysis of the extinction conditions for X-ray powder as
temperature of 1023 K was chosen to achieve complete reac- well as single crystal data led to the tetragonal space group
I4 /amd as the most likely choice. However, only the positions
1
of the heavier anions could be determined from the X-ray dif-
fraction data. E and nitrogen realize the same motif as was
deduced for iodine and nitrogen in Li IN . With the aim to
7
2
localize all lithium positions we performed neutron powder
diffraction at ambient and lower temperatures down to 3 K.
Close inspections of the patterns revealed the presence of the
reflection with Miller index (310). This reflection violates the
extinction condition for the a-glide plane perpendicular to
Table 1. Li
8
SeN
2
: Crystal structure data from single-crystal X-ray dif-
fraction.
Formula
8
Li SeN
2
Cryst. size /mm
Crystal system
Space group
a /Å
0.05 × 0.05 × 0.03
tetragonal
1
I4 md (No. 109)
7.060(2)
9.9689(7)
496.85(9)
4
c /Å
3
V /Å
Z
D
calcd. /g·cm–3
2.172
μ(Mo-K
T /K
α
) /mm–1
7.38
298
hkl range
± 11, ± 11, ± 16
70.1
2θ max, deg
Refl. measured
Refl. unique
3949
606
R
int
0.076
Param. refined
34
BASF
0.02(4)
0.043/0.070
1.19
2
R(F)/wR(F )
2
GooF (F )
Figure 1. DTA diagrams of reactions of (1) lithium with E and (2)
lithium, E with Li N (top: E = Se, bottom: E = Te).
–3
Δρfin /e·Å
1.64
3
Z. Anorg. Allg. Chem. 2010, 936–946
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
937

R. Niewa et al.
ARTICLE
2
8 2
Table 2. Li SeN : Positional parameters and displacement parameters Uij and Ueq (in Å ) from single-crystal X-ray diffraction.
Atom Site x
y
z
U
11
U
22
U
33
U
12
U
13
U
23
U
eq
Se
N
4a
8b
0
0
0.89813(9)
0.0093(5) 0.0193(5) 0.0109(2)
0
0
0
0
0
0.0132(1)
½
0.2671(6) 0.0003(3)
0.011(1)
0.021(3)
0.013(4)
0.029(8)
0.022(6)
0.007(2)
0.024(3)
0.032(5)
0.019(7)
0.05(1)
0.006(2)
0.018(3)
0.029(4)
0.030(8)
0.016(7)
0.003(2) 0.0079(7)
Li(1) 16c 0.7644(9) 0.188(1)
0.0773(6)
0.191(1)
0.962(2)
0.383(2)
0.002(2) –0.002(2) 0.003(2) 0.021(1)
Li(2) 8b
Li(3) 4a
Li(4) 4a
½
½
½
0.151(2)
0
0
0
0
0
0
0
0
0.018(4) 0.025(2)
0
0
0.026(3)
0.029(4)
Table 3. Selected data of Rietveld refinements: simultaneous X-ray and neutron diffraction refinements at 300 K and single neutron diffraction
refinements at 3 K. Number of refined structural parameters: 17. Radiation: Cu-Kα1 or λ = 1.5482 Å, respectively.
Composition
Li
8
SeN
2
Li
8
TeN
2
X-ray
neutron
00 K
neutron
3 K
X-ray
neutron
300 K
neutron
3 K
3
Unit cell parameter a /Å
Unit cell parameter c /Å
7.048(1)
9.995(1)
22.3–125.0
0.05
11.4
0.041, 0.058
7.024(1)
9.953(1)
22.3–125.0
0.05
7.217(1)
7.190(1)
10.234(1)
12.3–124.0
0.05
10.284(1)
2
θ-range /deg
10.1–90.0
0.01
10.1–90.012.3–124.0
Step size /deg
0.01
0.05
3.17
0.036, 0.057
2
χ
6.99
3.53
R
profile, RBragg
0.107, 0.098
0.023, 0.038
0.064,
0.022, 0.035
0.061
8 2
Table 4. Li EN : Positional parameters and isotropic displacement pa-
2
[
001] (hk0: h = 2n), indicating I4 md as the correct space group
1
rameters Beq (in Å ). First line from simultaneous X-ray and neutron
powder diffraction at 300 K, second line in bold from neutron powder
diffraction at 3 K.
choice. Apparently, the intensity contributions of lithium in the
neutron powder diffraction experiments produce this reflection
(
b (Li) = –1.90 fm; b (N) = 9.36 fm; b (Se) = 7.97 fm; b (Te) =
c c c c
.80 fm [20]) which has too low intensity to be observed in
Atom Site
x
y
z
B
eq
5
Se
4a
0
0
0.8983(5)
1.22(7)
0.67(4)
0.77(4)
0.51(2)
2.3(1)
1.7(1)
3.3(3)
2.5(2)
2.9(5)
2.1(3)
3.2(6)
2.1(3)
X-ray powder diffraction due to the small scattering contribu-
tion of lithium. In other words, the anionic substructure is (ap-
proximately) centrosymmetric, whereas the Li-substructure is
acentric. With this information the positional parameters of all
atoms could be deduced from geometric considerations and
refined against both powder diffraction patterns and single-
crystal X-ray diffraction data. Table 1 and Table 2 gather crys-
tallographic and technical data for the structure determination
0.8981(3)
N
8b
½
0.2678(3)
0
0
.2681(2)
Li(1) 16c 0.772(1)
0.183(2)
0.182(1)
0.152(2)
0.077(1)
0.077(1)
0.199(2)
0.199(1)
0.949(3)
0.775(1)
Li(2) 8b
Li(3) 4a
½
½
½
0
0
.154(1)
0
.950(2)
0.398(3)
.398(2)
of Li SeN from single-crystal X-ray diffraction. Table 3 and Li(4) 4a
0
0
8
2
0
Table 4 present the respective data for simultaneous Rietveld
refinements of X-ray and neutron powder patterns at ambient Te
temperature for both compounds and for neutron diffraction
4a
8b
0
0.8969(3)
0.8962(1)
0
1.20(2)
0.76(2)
1.20(2)
0.84(1)
1.7(1)
N
½
0.2686(2)
patterns at 3 K. Figure 2 graphically depicts exemplarily the
results of the Rietveld refinements for Li TeN based on simul-
0
.2693(1)
8
2
Li(1) 16c 0.7541(8)
0.1871(9)
0.1866(4)
0.157(1)
0.0787(6)
0.0778(3)
0.193(1)
0.1939(4)
0.957(1)
taneous treatment of X-ray and neutron powder diffraction pat-
terns taken at 300 K. Refinement data on neutron diffraction Li(2) 8b
patterns for further temperatures are available as supplemen-
0.7583(4)
1.55(5)
2.5(1)
½
½
½
0
0
.1549(6)
1.58(7)
2.9(3)
Li(3) 4a
tary data. After those structure refinements were finished it
came to the best of our knowledge, that neutron powder dif-
fraction at ambient temperature had earlier been carried out in
the frame of a habilitation thesis [17]. The resulting structural
data are nearly identical.
0
.9560(7)
2.4(1)
Li(4) 4a
0
0.373(1)
3.7(4)
0.3805(7)
2.5(1)
According to our structure refinements Li SeN and Li TeN
8
2
8
2
are isotypes. In the following we will discuss the structure pe-
culiarities by using the distances from simultaneous X-ray and ces for Li SeN can be taken from Table 5. Figure 3 utilizes
8
2
neutron powder diffraction, since the positions of lithium anisotropic displacement parameters from the single crystal
should be more precisely determined. For sake of simplifica- diffraction refinement to emphasize the displacement of lith-
tion we use the distances in Li TeN , the corresponding distan- ium atoms.
8
2
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 936–946

8 2 8 2
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
8 2
Figure 3. Li SeN : Coordination of lithium (large grey ellipsoids) by
nitrogen (smaller grey ellipsoids) and selenium (dark ellipsoids). Inter-
atomic distances > 3 Å are indicated by dashed lines. Anisotropic dis-
placement ellipsoids are taken from the single-crystal X-ray data and
depicted with 99 % probability.
edge lengths in the range of 3.3175(5) Å to 3.8736(5) Å. The
chalcogenide atoms are localized in the large voids of this
frame within so-called Friauf polyhedra.
Figure 2. Li
8 2
TeN : X-ray (Cu-Kα1 radiation, top) and neutron (λ =
1
.5482 Å, bottom) powder diffraction diagrams. The measured data
are shown as points, the continuous line represents the calculated pro-
file and the lower line shows the difference between the calculated
and observed intensities. Marks below the data indicate positions of
calculated Bragg reflections. The inset enlarges the reflection (310)
1 1
calling for the space group choice I4 md rather than I4 /amd (low in-
tensity reflections at 2θ of about 42.8° and 44.8° are due to a minor
unknown impurity).
8 2
Table 5. Li EN : Selected interatomic distances (in Å) from simultane-
ous X-ray and neutron powder diffraction at 300 K. First line: E = Se,
second line in bold: E = Te.
Figure 4. Li
8 2
EN : Chalcogenide ions E = Se, Te (dark spheres) embed-
N–Li(1)
2.15(1)
.090(6)
2.17(1)
.25(6)
2.02(1)
.098(8)
2.15(2)
.15(1)
1.955(8)
.990(3)
2.20(2)
.10(1)
2× E–N
≥ 3.990(4)
ded in a framework of vertex-sharing (empty) tetrahedra of nitrogen
(light grey spheres) with the structural motif of a cubic Laves phase.
2
≥ 4.231(1)
N–Li(1)
N–Li(2)
N–Li(2)
N–Li(3)
N–Li(4)
2×
2
E–Li(1)
2.73(1)
2.910(6)
2.84(1)
2.956(6)
2.50(4)
2.81(1)
4×
4×
1×
Lithium atoms fill the space within the anionic framework,
which leads to the quite high coordination number of 9 for
nitrogen (for comparison in α-Li N: CN(N) = 8 [16], for the
modifications at higher pressures β-Li N: CN(N) = 11, γ-Li N:
3 3
CN(N) = 6 + 8 [21]) in a distorted capped quadratic antiprism.
The interatomic distances are with d(Li–N) = 2.090(6) Å –
2×
1×
1×
1×
2
E–Li(1)
E–Li(4)
3
2
1
2
.225(6) Å slightly longer than in α-Li N, which can be easily
3
2
rationalized from the different coordination numbers for nitro-
gen. Under consideration of Li–Te distances d(Li–Te) < 3 Å
for the first coordination sphere (Li Te: d(Li–Te) = 2.82 Å
2
The anionic substructure of nitrogen and E resembles the [22]) tellurium is coordinated by 9 lithium atoms in a capped
atomic arrangement in cubic Laves phases, e.g., MgCu . Nitro- tetragonal cuboid (Figure 5). However, the surrounding of the
2
gen occupies the position of copper, which leads to a three- four crystallographic positions of lithium are largely different
dimensional framework of vertex-sharing (empty) tetrahedra (Figure 3): considering the same maximum distances d(Li–Te)
(Figure 4). These tetrahedra are significantly distorted with < 3 Å Li(1) is tetrahedrally coordinated by two nitrogen atoms
Z. Anorg. Allg. Chem. 2010, 936–946
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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939

R. Niewa et al.
ARTICLE
and two tellurium atoms and Li(2) is in trigonal somewhat
non-planar coordination by nitrogen (angular sum 341.5°)
completed by a tellurium atom at a clearly longer distance of
3
.24(1) Å. The surrounding of Li(4) is trigonal planar formed
by two nitrogen and one tellurium atom. Different from those
environments is the Li(3) coordination by two nitrogen atoms
with a bonding angle of 154.13(3)°. This twofold coordination
is indicated by distances below 2 Å and the longer distance
to tellurium of 3.19(1) Å. As is also indicated by quantum
mechanical calculations and NMR spectroscopic investigations
this arrangement leads to a clearly different bonding situation
as compared to the three other lithium sites (cf. NMR part).
Figure 6. Li
8
EN
2
: Group-subgroup scheme [23] for the anionic sub-
2
structure derived from the cubic Laves phase MgCu . The left part
represents the symmetry reduction (translationsgleiche (t) and index)
and unit cell transformation. The relationship between the atomic coor-
dinates is shown on the right.
8 2
Figure 5. Li EN : Capped cuboid as first coordination environment of
E = Se, Te (dark spheres) by lithium (small light grey spheres). The
second coordination (Friauf polyhedron) formed by nitrogen (larger
grey spheres) is indicated by dashed lines. Exemplarily, the coordina-
tion of three nitrogen atoms by lithium in form of distorted capped
square anti-prisms is given.
A number of cubic Laves phases are able to intercalate sig-
nificant amounts of hydrogen under preservation of the general
structural motif of the metal atoms although undergoing crys-
tallographic symmetry reductions [27]. In the context of the
title compounds it is particularly interesting to compare with
the hydrogen-rich compounds LaMg D , CeMg D [28] and
The relation to the cubic Laves phase MgCu can be most
2
2
7
2
7
comfortably be derived in terms of a group-subgroup Scheme
SmMg D7 [29]. Upon hydride formation the cubic Laves
2
after Bärnighausen [23] as is depicted in Figure 6. Starting
phases distort to tetragonal metric with space group P4 2 2. In
1
1
¯
from the space group type Fd3m of the Laves phase MgCu2
the resulting crystal structures the deuterium occupies posi-
tions in trigonal planar and tetrahedral coordination by either
exclusively magnesium or rare-earth metal and magnesium.
However, one crystallographic site is situated in the tetrahedra
the tetragonal space group I4 /amd results from a translations-
1
gleiche symmetry reduction with index 3 with a' = (a – b)/2,
b' = (a + b)/2, c' = c. A second translationsgleiche reduction
with index 2 leads to the non-centrosymmetric space group
I4 md and the respective positions of the anions in Li EN .
formed by magnesium. This position is unoccupied in Li EN2
8
1
8
2
(
whereas it is partly occupied by germanium in the aforemen-
The crystal structure of the title compounds resemble that of
the structure family of Argyrodites (mineral Ag GeS [24]).
tioned Argyrodites). Nevertheless, the rare-earth metal in the
deuterides is higher coordinated by D (twelve-fold) than E by
lithium in the title compounds (ninefold). On the other hand
magnesium is sevenfold and nitrogen ninefold coordinated, re-
spectively. This example underlines the structural stability of
the Laves phase arrangement if a reasonable radii ratio is pro-
vided together with an extremely high structural variety for
intercalation of small atoms.
8
6
¯
In the cubic high-temperature phases (space group F43m) of
Argyrodites the chalcogenide realizes the motif a three-dimen-
sional tetrahedral network of edge-sharing tetrahedra in the ar-
rangement of copper in the cubic Laves phase MgCu . How-
2
ever, these tetrahedra are partly filled by germanium leading
to a stacking of tetrahedra GeS and further sulfur. Argyrodites
4
are extremely flexible in their compositions. They may be de-
n+ 2–
–
scribed with the general formula A(12–n)B E (6–y)X with e.g.
y
Temperature Dependent Diffraction Experiments
A = Li, Cu, Ag; B = P, As, Si, Ge; E = S, Se; X = Cl, Br, I
and generally are known as Cu-, Ag- and Li-ionic conductors
Since the displacement parameters of particularly lithium at
room temperature are comparably large we have studied the
[25, 26].
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40
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8 2 8 2
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
crystal structures of the title compounds additionally by neu-
tron diffraction at 3, 50, 100, 150, 200, 250 K to derive a
reliable structure model. No indication for a structural transi-
tion was observed in these measurements. This finding agrees
with the fact that DSC measurements in the temperature range
of 175 K – 670 K did not show any significant signal possibly
related to a phase transition. On cooling the c/a ratio monotoni-
cally decreases, however, the ideal value of √2 for a cubic
metric is not reached even at 3 K (Figure 7 and Figure 8). Fig-
ure 9 shows the temperature dependence of the isotrope dis-
placement parameters as exclusively derived from these neu-
tron diffraction experiments. Besides some scatter, all
displacement parameters shrink with decreasing temperature.
However, extrapolation of the values for nitrogen and E to zero
K results in small but finite values. The extrapolated displace-
ment parameters for the different sites occupied by lithium
give quite large values indicating a significant static contribu-
tion additional to the vibration dominating at higher tempera-
tures.
8 2
Figure 8. Li EN : Temperature dependence of the unit cell volume V
and the ration c/a from neutron powder diffraction (full symbols) and
from high resolution X-ray powder diffraction using synchrotron radia-
tion (open symbols) for top: E = Se, and bottom: E = Te.
with those from neutron powder diffraction with only a small
offset. With increasing temperature the unit cell parameters
monotonically increase (Figure 7 and Figure 8). However,
above 500 K the c/a ratio exhibits a kink to a different slope
followed by a maximum at 700 K and a decreasing ratio at
higher temperatures. At such high temperatures the title com-
pounds slowly decompose with formation of Li E, the unit cell
2
volume of Li EN determined at room temperature after the
8
2
heating circle is slightly smaller than the initial volume indicat-
ing a slight change of composition. Simultaneously, the colors
of the samples slightly darken. Li EN expands quite normally
8
2
under heating up to ~800 K and expansion increases in the
range where the second phase appears. Relative expansion pa-
rameters along the a- and c-axes indicate a nearly isotropic
behavior in the studied temperature range until onset of de-
composition.
8 2
Figure 7. Li EN : Temperature dependence of the unit cell parameters
a and c from neutron powder diffraction (full symbols) and from high
resolution X-ray powder diffraction using synchrotron radiation (open
symbols) for top: E = Se, and bottom: E = Te.
NMR Spectroscopy and Quantum Mechanical Calculations
High-resolution powder diffraction studies at elevated tem-
To study the chemical bonding of the different lithium atoms
peratures up to 1000 K were carried out applying synchrotron in Li SeN and Li TeN NMR spectroscopy in combination
8
2
8
2
radiation. Again the data indicate no structural transition in the with quantum mechanical calculations was applied. This ap-
studied temperature range in agreement with DSC measure- proach was successfully used in the past for various classes of
ments. At ambient temperatures the curves nearly coincide compounds [30–32]. Since the title compounds are electrically
Z. Anorg. Allg. Chem. 2010, 936–946
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
941

R. Niewa et al.
ARTICLE
outstanding anisotropy of the charge distribution compared to
the other lithium atoms. For comparison the EFGs in α-Li N
3
determined by NMR spectroscopic experiments are 0.58 MHz
and 0.28 MHz for the twofold and the threefold coordinated
lithium atoms, respectively [36]. Quantum mechanical calcula-
tions are in good agreement with these results. The origin of
the EFGs was attributed to a polarization of the charge distri-
bution of the lithium atoms [30]. This polarization induced by
chemical bonding can also be expected to be the largest for
Li(3) in Li SeN and Li TeN since the Li–N distances of
8
2
8
2
1
.955(8) Å and 1.990(3) Å, respectively, are significantly
shorter than for the other lithium atoms (Table 5). This corre-
sponds to the situation in α-Li N with 1.939 Å and 2.130 Å
3
for the twofold and threefold coordinated lithium atoms, re-
spectively [16]. Considering the different values of the EFGs
of the title compounds the lithium environments might be dis-
tinguishable by NMR spectroscopic experiments.
The non-referenced calculated isotropic chemical shifts (δiso)
are quite similar for all lithium atoms, thus it can not be ex-
pected to resolve separated NMR spectroscopic signals experi-
mentally. With respect to the anisotropy of chemical shielding
(
δaniso) Li(3) also differs from the other lithium atoms, which
indicates an exceptional bonding situation of Li(3) (Table 6).
7
The static and magic angle spinning (MAS) Li NMR signals
of Li SeN and Li TeN recorded at ambient temperature are
8
2
8
2
depicted in Figure 11. The full spectral width of the signals
indicates the presence of quadrupole coupling being due to
interactions of the EFG at the nuclear sites with the nuclear
quadrupole moments. This can also be seen by the number
of rotational side bands of the MAS NMR signals. The main
transition in the centre of the signal is almost symmetric and
covers a comparably small frequency range being in agreement
with simulations of the NMR signals based on the quantum
mechanical calculations. The individual signal contributions
can not be resolved by application of MAS, but the average
isotropic chemical shift can be determined (see Table 6 and
inset of Figure 11).
To investigate motional processes of the lithium atoms tem-
perature dependent NMR spectroscopic experiments were per-
formed. The full width at half maximum (FWHM) of the NMR
signals for both compounds differs significantly at ambient
temperature (Figure 11 inset). The assumption that dipole-di-
8 2
Figure 9. Li EN : Temperature dependence of the isotropic displace-
ment parameters from neutron powder diffraction (top: E = Se, and
bottom: E = Te).
non-conducting, chemical shielding (δ) and electric field gradi-
ent (EFG) can be calculated with quantum mechanical methods
[
33–35]. This allows an estimation of the expected NMR spec-
troscopic signals and provides information about the bonding
situation of the atoms.
The results of the quantum mechanical calculations of NMR
spectroscopic parameters for the structure models obtained by
neutron powder diffraction at 3 K and the geometrically opti-
mized structures of Li SeN and Li TeN are very similar for
8
2
8
2
both compounds (Table 6). The bonding situations of the lith- pole coupling is the dominant mechanism of the NMR signal
ium atoms at the four different sites apparently differ since line broadening already indicates motional processes of the
their EFGs vary considerably. A visualization of the EFGs as lithium atoms, which average the coupling. The temperature
7
ellipsoids with respect to their environment is depicted exem- dependence of the FWHM and the corresponding Li NMR
plarily for Li TeN in Figure 10. To emphasize the orientation signals show a dramatic change of the NMR signal line shape
8
2
of the tensors, which can only be obtained by quantum me- (Figure 12). At low temperatures the main transition signal is
chanical calculations for powder samples, the directions of the broadened and the satellite transitions are clearly visible, re-
three principal axes V are indicated. No significant differences sulting in an elaborated line shape of the NMR signals. At
ii
of the orientations were obtained for Li SeN , which indicates high temperatures only a narrow NMR signal remains for both
8
2
a high similarity of the bonding situation of the lithium atoms compounds. The change of the NMR signal line shape indi-
in both compounds. The sizes of the ellipsoids corresponding cates an averaging of the quadrupole coupling in addition. A
to the anisotropy of the charge distribution at the nuclear sites continuous decrease of the FWHM of the main transition NMR
clearly decrease with increasing coordination number accord- signal with increasing temperature is observed for Li
SeN and
2
8
ing to CN = 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), Li TeN (Figure 12 insets). In contrast a dramatic reduction
8
2
and Li(1), respectively. The large EFG of Li(3) indicates an of the FWHM resulting from a spontaneous onset of lithium
9
42 www.zaac.wiley-vch.de
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8 2 8 2
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
7
Table 6. Li NMR parameters for Li
8
SeN
2
and Li
8
TeN
2
obtained by quantum mechanical calculations and least-square fits of the low temperature
of the chemical shielding as
for the lithium sites are given. The
frequency sweep NMR signals (experiment). The isotropic shift δiso, anisotropy δaniso and asymmetry parameter η
well as the quadrupolar coupling constant C and the asymmetry parameter of the quadrupolar coupling η
sign of the quadrupolar coupling constant can not be determined by NMR experiments. The average referenced isotropic shift of the lithium
atoms is determined by the maxima of the MAS signals recorded at ambient temperature using a rotation frequency of 15 kHz. The calculated
isotropic shifts are not referenced. Only the differences of the individual calculated values are of interest for that reason.
δ
Q
Q
Li
8
SeN
2
8 2
Li TeN
δ
iso /ppm
δ
aniso /ppm
η
δ
C
Q
/MHz
η
Q
δ
iso /ppm
δ
aniso /ppm
η
δ
C
Q
/MHz
η
Q
Based on structure model obtained by neutron diffraction experiments at T = 3 K
Li(1)
Li(2)
Li(3)
Li(4)
–84.73
–83.40
–82.55
–85.16
–3.96
3.78
–17.60
5.15
0.44 0.24
0.17 –0.36
0.06 0.68
0.52 –0.31
0.92
0.12
0.26
0.13
–85.16
–83.67
–83.93
–85.29
–4.61
3.97
–15.81
5.40
0.39 0.30
0.27 –0.31
0.05 0.65
0.24 –0.33
0.54
0.12
0.24
0.67
Based on geometrical optimized structure model
Li(1)
Li(2)
Li(3)
Li(4)
–84.85
–83.09
–83.06
–85.04
–4.54
3.82
–18.30
5.37
0.29 0.27
0.61 –0.37
0.03 0.73
0.40 –0.34
0.67
0.20
0.15
0.56
–85.14
–83.58
–83.96
–85.33
–4.95
4.02
–15.99
5.51
0.35 0.32
0.47 –0.31
0.03 0.66
0.48 –0.34
0.46
0.23
0.22
0.77
Experiment
Li(1)
Li(2)
Li(3)
Li(4)
0.26(2)
0.5(1)
0.2(1)
0.2(1)
0.5(1)
0.27(2)
0.6(1)
0.2(1)
0.2(1)
0.7(1)
0.35(2)
0.33(2)
4.3
–
–
4.0
–
–
0.65(2)
0.30(2)
0.59(2)
0.29(2)
Figure 10. Visualization of the EFGs by ellipsoids obtained from
quantum mechanical calculations for the geometrically optimized
structure of Li
8 2
TeN . The spatial orientations of the principal axes Vii
are indicated.
diffusion accompanied by a phase transition is reported e.g. for
the Argyrodite Li PS I [37, 38]. The continuous change of the
FWHM for the title compounds evidences the absence of a
phase transition of the title compounds being in agreement
with the diffraction experiments.
6
5
7
8 2 8 2
Figure 11. Static and MAS Li NMR signals for Li SeN and Li TeN .
The decrease of the signal width with temperature differs for
Li SeN and Li TeN (Figure 12 insets). Whereas for Li SeN
8
2
8
2
8
2
a constant signal width seems to be reached below 150 K it is range. Additional NMR spectroscopic measurements of the
not yet clear for which temperature a constant FWHM of the FWHM at lower temperatures are required for this purpose.
Li TeN NMR signals is reached since the values decrease Above 350 K and 450 K a constant signal width is observed
8
2
with increasing temperature in the investigated temperature for Li SeN and Li TeN , respectively. This indicates differen-
8
2
8
2
Z. Anorg. Allg. Chem. 2010, 936–946
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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943

R. Niewa et al.
ARTICLE
7
Figure 12. Temperature dependent Li NMR spectroscopic measurements of Li
8
SeN
2
(left) and Li
8
TeN
2
(right) with an analysis of the full width
at half maximum (FWHM) as a function of temperature (inset). Error bars of ± 0.5 kHz for the FWHM are indicated.
ces of the motional processes of the lithium atoms for both atoms are frozen, frequency sweep NMR experiments were
compounds.
performed at 15 K (Figure 13). Remarkably different NMR
7
In order to resolve the different Li NMR signal contribu- line shapes for both compounds are observed at this tempera-
tions and to ensure that the motional processes of the lithium ture. Whereas the NMR signal of Li TeN is well elaborated
8
2
showing clearly the features of the individual signal contribu-
tions, the signal of Li SeN is smeared out and characteristic
8
2
features of the signal contributions are only weekly indicated.
This difference points at a high level of residual disorder in
Li SeN and is confirmed by detailed line shape analysis of
8
2
the NMR signals. Using the results of the quadrupole coupling
parameters obtained by the quantum mechanical calculations
as a starting model the experimental values were quantified by
least-squares fits of the NMR signals (Table 6). Both NMR
experiments and quantum mechanical calculations are in good
agreement confirming experimentally the anisotropy of the
charge distribution in the vicinity of the nuclear sites of the
lithium atoms determined by quantum mechanical methods.
Conclusions
The title compounds show Li-motional processes according
to solid state NMR spectroscopy. An anomalous thermal ex-
pansion in non-ion conducting phases, which precedes a transi-
tion to an ion conducting phase, seems to be characteristic for
some solid ion conductors (see [39] and references cited
therein), in particular when they undergo an abrupt transition
into the ion conducting state. The compounds Li EN (E = Se,
Te) do not suffer any clearly recognizable transition in the full
temperature range from 3 K to close to 800 K according to
diffraction data. The observation of lithium motion by NMR
spectroscopy without a sharp structural transformation to an
8
2
7
Figure 13. Li frequency sweep NMR spectroscopic measurements at
8 2 8 2
T = 15 K for Li SeN (bottom) and Li TeN (top). Data points of the
various experiments are indicated by open circles. The full line repre-
sents the result of the least-squares fit and the dashed lines the individ-
ual signal contributions.
9
44
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 936–946

8 2 8 2
Synthesis, Crystal Structure and Lithium Motion of Li SeN and Li TeN
ion conducting phase could imply that Li TeN and Li SeN
2
are type II or type III ion conductors according to classification
by Keen [40].
recorded for a duration of 9 min. Due to apparent chemical reactions of
Li SeN the measurements were restricted to a maximum of 900 K
with recording times of 15 min per pattern. Further details of the crys-
tal structure investigation may be obtained from the Fachinformations-
zentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax:
8
2
8
8
2
The anisotropy of the charge distribution of the lithium at-
oms differs considerably for the four crystallographic sites in
Li EN with E = Se and Te, respectively. A clear correlation of
+
49-7247-808-666; E-Mail: crysdata@fiz-karlsruhe.de, http://
8
2
www.fiz-informationsdienste.de/en/DB/icsd/depot_anforderung.html)
on quoting the depository number CSD-421252.
the anisotropy of the charge distribution and the coordination
number of the lithium atoms is recognized. Good agreement
of NMR spectroscopic experiments and quantum mechanical
calculations of NMR spectroscopic parameters is obtained.
Neutron Powder Diffraction
The samples were placed in argon-filled cylindrical vanadium contain-
ers (diameter 8 mm; length 51 mm; wall thickness 0.15 mm) and
sealed with indium gaskets. Patterns were collected at 3, 50, 100, 150,
Experimental Section
Preparation
200, 250 and 300 K at the SPODI diffractometer of FRM II with the
All manipulations were carried out under dry argon in a glovebox wavelength of 1.5482 Å.
(
(
p(O
2 2 3
,H O) < 0.1 ppm). Li N was prepared from elemental lithium
rods, Alfa, 99.9 %) and nitrogen (Messer-Griesheim, 99.999 %, addi-
Structure Refinements
tionally purified by passing over molsieve, Roth 3 Å, and BTS cata-
lyst, Merck) of ambient pressure at 670 K. The lithium chalcogenides
For all Rietveld refinements the program package FULLPROF [43]
was used. For all refinements against powder data the fractional coor-
dinate z of nitrogen (highest contribution to neutron diffraction due to
high diffraction length) was fixed to zero. The crystal structure of
Li SeN based on data from single crystal diffraction intensity collec-
8 2
tion was refined with the program system SHELXL-97–2 [44].
Li
ampoules at 575 K and 775 K, respectively. For synthesis of Li
and Li TeN appropriate molar ratios of Li N und Li E were reacted
2
E (E = Se, Te) were obtained from the elements in sealed tantalum
8
SeN
2
8
2
3
2
at 1023 K in sealed tantalum ampoules. The products were microcrys-
talline orange powders with a slightly darker color for the tellurium
compound. Both ternary nitrides are sensitive against moist air.
In synthesis experiments with excess lithium small single crystals of
Li SeN were obtained using the above mentioned conditions.
8 2
Chemical Analyses
Chemical analyses for N and O were carried out by hot-gas-extraction
(
LECO 436 DR). lithium, selenium, and tellurium were quantified ap-
plying the inductively coupled plasma-optical emission spectrometry
ICP-OES, Varian, VISTA RL) method.
Thermal Analysis
(
Difference scanning calorimetry was performed with a DSC 204 Phoe-
nix (Netzsch) in argon-filled sealed aluminum crucibles. DTA/TG
measurements (STA 409, Netzsch, Nb crucibles, thermocouple type S)
were performed under nitrogen and argon to analyze the formation of
the ternary compounds, to find the optimum reaction conditions, and
to examine the decomposition behavior. Temperature calibration was
carried out with five melting points of pure metals.
NMR Spectroscopy and Quantum Mechanical Calculations
7Li NMR spectroscopic investigations were performed by using a
Bruker AVANCE spectrometer with a magnetic field of B
The corresponding resonance frequency of the Li isotope is
0
= 11.74 T.
7
1
94.373 MHz. The NMR signals are referenced to a saturated solution
of LiCl in D O.
2
X-ray Diffraction
Magic angle spinning (MAS) NMR spectroscopic experiments were
In-house X-ray powder diffraction pattern were taken in transmission carried out for different rotation frequencies at ambient temperature on
(STADIP, STOE) with Cu-Kα1 radiation.
powder samples of Li SeN2 and Li TeN2 filled into ZrO2 rotors
8
8
(
4.0 mm diameter) using a Bruker double resonance MAS probe. Full
8 2
X-ray diffraction on a single crystal Li SeN (sealed in a glass capil-
recovery of the magnetization at ambient temperature was achieved
within 1.0 s. Single pulse experiments with hard pulses of 3.5 μs dura-
tion were applied for the selenium compound. An echo pulse sequence
lary) was performed with a MSC-Rigaku R-Axis Rapid diffractometer
-radiation. An absorption correction based on symme-
applying Mo-K
α
try-equivalent reflections was applied [41].
with pulses of equal duration of 2.5 μs was used for Li
8 2
TeN . The
interpulse delay was synchronized with the rotation frequency.
In situ crystal structure investigations between room temperature and
1
098 K were carried out with high-resolution powder diffraction apply-
Wide line variable-temperature 7Li NMR signals were recorded for
randomly oriented crystallites of Li SeN and Li TeN enclosed in a
ing synchrotron radiation (beamline B2, HASYLAB at DESY). The
diffraction experiments were performed in Debye–Scherrer capillary
geometry with the samples sealed in quartz capillaries using an on-site
readable image plate detector OBI [42]. The wavelength of 0.65131 Å
8
2
8
2
sealed glass ampoule over a temperature range of 125 K to 525 K.
Depending on the spectral width at different temperatures either single
pulse experiments with hard pulses of 3.0 μs duration or an echo se-
quence with pulses of equal duration of 1.5 μs were applied. The inter-
pulse distance of the echo sequence was optimized to 100 μs to avoid
distortions of the NMR signal line shape.
was calibrated using the reflection positions of LaB
60a) reference material. The typical full-width at half-maximum
FWHM) of reflections obtained in this geometry was 0.06–0.08°. A
STOE furnace was used for in situ HT diffraction experiments. For
Li TeN
6
(NIST SRM
6
(
7
8
2
patterns were taken from room temperature to 548 K in steps Frequency sweep Li NMR spectroscopic experiments at 15 K were
of 25 K, and from 598 K to 1098 K in steps of 100K. All patterns were performed on the powder samples of Li
8
SeN
2
and Li
8
TeN
2
mounted
Z. Anorg. Allg. Chem. 2010, 936–946
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
945

R. Niewa et al.
ARTICLE
nd
on a low-Q probe with automatic tuning and matching built by NMR- [19] Binary Alloy Phase Diagrams 2 Ed. (Ed.: T. B. Massalski),
ASM International, Materials Park, Ohio 1990.
20] International Tables for Crystallography, Volume C, 5 Edition
Ed.: T. Hahn), Kluwer Academic Publishers, 2002.
Service (Erfurt, Germany). The temperature was adjusted in a helium
cryostat system. A series of selective excitation experiments was ap-
plied using low-power pulses of 100 μs.
th
[
[
[
(
21] H. U. Beister, S. Haag, R. Kniep, K. Strossner, K. Syassen,
Angew. Chem. Int. Ed. Engl. 1988, 27, 1101–1103.
22] E. Zintl, A. Harder, B. Dauth, Z. Electrochem. Angew. Phys.
Chem. 1934, 40, 588–593.
NMR signals were simulated using the SIMPSON [45] program pack-
age using δiso = 1/3 (δXX + δYY + δZZ), δaniso = δZZ – δiso and η
XX – δYY) / δaniso for the isotropic, the anisotropic, and the asymmetry
parameter of the chemical shielding, respectively. The order of the
principal axes of the shielding tensor is defined by |δZZ – δiso| ≥ |δXX
δ
=
(δ
[
[
23] H. Bärnighausen, MATCH 1980, 9, 139–173.
24] V. M. Goldschmidt, Z. Kristallogr. Mineral. 1909, 45, 548–554;
–
C. Palache,H. Berman,C. Fondel, Dana’s System of Mineralogy,
th
δ
iso| ≥ |δYY – δiso| resulting in 0 ≤ η
δ
≤ 1. The quadrupole coupling
7
Ed. 1944, pp. 356ff.
constant is defined as C
moment Q( Li) = –4.01 fm [46] and the main principal component of
the electric field gradient VZZ. The asymmetry parameter of the quadru-
pole coupling is defined as η
≥
Q
= e Q VZZ / η with the nuclear quadrupole [25] T. Nilges, A. Pfitzner, Z. Kristallogr. 2005, 220, 281–294.
7
2
[26] H.-J. Deiseroth, S.-T. Kong, H. Eckert, J. Vannahme, C. Reiner,
T. Zaiß, M. Schlosser, Angew. Chem. Int. Ed. 2008, 47, 755–758.
[
27] H. Kohlmann, F. Fauth, P. Fischer, A. V. Skripov, V. N. Koz-
hanov, K. Yvon, J. Alloys Comp. 2001, 327, L4–L9 and references
given therein.
Q
= (VXX – VYY) / VZZ with |VZZ| ≥ |VXX|
|VYY| and 0 ≤ η ≤ 1.
Q
[
28] F. Gingl, K. Yvon, T. Vogt, A. Hewat, J. Alloys Compd. 1997,
Quadrupole coupling and chemical shift parameters were calculated
using the NMR-CASTEP [33] code, within periodic boundary condi-
tions and the pseudopotential approximation using the GIPAW [47]
2
53, 313–317.
[
29] H. Kohlmann, F. Werner, K. Yvon, G. Hilscher, M. Reissner, G. J.
Cuello, Chem. Eur. J. 2007, 13, 4178–4186.
and PAW [34, 48] methods. On-the-fly generated ultrasoft pseudopo- [30] P. Blaha, K. Schwarz, P. Herzig, Phys. Rev. Lett. 1985, 54, 1192–
tentials were used for the calculations. The calculations were per-
formed with a cut-off energy of 450 eV and with 4 × 4 × 5 k points
using GGA (PBE [49]). Geometry optimizations were also performed
using the code. The model of the crystal structure obtained at 3 K
using neutron powder diffraction was used as basis for the geometry
optimization.
1195.
[
31] F. Haarmann, K. Koch, D. Grüner, W. Schnelle, O. Pecher, R.
Cardoso-Gil, H. Borrmann, H. Rosner, Yu. Grin, Chem. Eur. J.
2
009, 15, 1673–1684.
[
[
[
32] S. E. Ashbrook, L. Le Pollès, R. Gautier, C. J. Pickard, R. I. Wal-
ton, Phys. Chem. Chem. Phys. 2006, 8, 3423–3431.
33] S. J. Clark, M. D. Segall, C. J. Pickard, P. J. Hasnip, M. J. Prob-
ert, K. Refson, M. C. Payne, Z. Kristallogr. 2005, 220, 567–570.
34] M. Profeta, F. Mauri, C. J. Pickard, J. Am. Chem. Soc. 2003, 125,
Supporting Information (see footnote on the first page of this article):
5
41–548.
Unit cell parameters at different temperatures are gathered in Ta- [35] J. R. Yates, C. J. Pickard, F. Mauri, Phys. Rev. B 2007, 76,
bles S1 – S4.
024401.
[
[
[
36] D. Brinkmann, W. Freudenreich, J. Ross, Solid State Commun.
1
978, 28, 233–237.
37] S.-T. Kong, H. J. Deiseroth, C. Reiner, Ö. Gün, E. Neumann, C.
Ritter, D. Zahn, Chem. Eur. J. 2010, 16, 2198–2206.
38] O. Pecher, S.-T. Kong, C. Reiner, H. J. Deiseroth, F. Haarmann,
D. Zahn, Chem. Eur. J. 2010, published online, DOI: 10.1002/
chem. 200902470.
39] D. Trots, A. Senyshyn, D. A. Mikhailova, T. Vad, H. Fueß, J.
Phys.: Condens. Matter 2008, 20, 455204.
40] D. A. Keen, J. Phys.: Condens. Matter 2002, 14, R819–R857.
Acknowledgement
We would like to thank Anja Völzke for performing the chemical analy-
ses, Susann Scharsach for DSC measurements and Yurii Prots for sin-
gle-crystal X-ray diffraction intensity data collection.
[
[
References
[41] R. Jacobson, Program REQAB, unpublished.
[
42] M. Knapp, V. Joco, C. Baehtz, H. H. Brecht, A. Berghaeuser, H.
Ehrenberg, H. von Seggern, H. Fueß, Nucl. Instrum. Methods
Phys. Res. A 2004, 521, 565–570.
[
1] H. Sattlegger, H. Hahn, Z. Anorg. Allg. Chem. 1970, 379, 293–
299.
[
2] H. Sattlegger, H. Hahn, Naturwissenschaften 1964, 51, 534–535.
3] P. Hartwig, W. Weppner, W. Wichelhaus, Mater. Res. Bull. 1979,
[
43] T. Roisnel, J. Rodriguez-Carvajal, WINPLOTR, Version May
th
[
2
000, Materials Science Forum, Proceedings of the 7 European
14, 493–498.
Powder Diffraction Conference Barcelona, Spain, 188, 2000; J.
Rodriguez-Carjaval, FULLPROF.2k, Version 1.6; 2000; Labora-
toire Léon Brillouin, in: Abstract of Satellite Meeting on Powder
Diffraction, Congress of the International Union of Crystallogra-
phy, Toulouse, France, 1990, 127.
[
4] P. Hartwig, W. Weppner, W. Wichelhaus, A. Rabenau, Angew.
Chem. Int. Ed. Engl. 1980, 19, 74–75.
[
5] K. Kitahama, Y. Furukawa, S. Kawai, O. Nakamura, Solid State
Ionics 1981, 3, 4, 335–339.
[
[
[
[
[
[
[
[
[
[
[
[
[
6] Y. Jia, J. Yang, Solid State Ionics 1997, 96, 113–117.
[44] G. M. Sheldrick, SHELXL-97–2, Program for the Refinement of
Crystal Structures, Universität Göttingen, Göttingen, Germany,
1997.
[45] M. Bak, J. T. Rasmussen, N. Ch. Nielsen, J. Magn. Reson. 2000,
147, 296–330.
[46] R. K. Harris, E. D. Becker, J. Magn. Reson. 2002, 156, 323–326.
[47] C. J. Pickard, F. Mauri, Phys. Rev. B 2001, 63, 245101.
[48] H. M. Petrilli, P. E. Blöchl, P. Blaha, K. Schwarz, Phys. Rev. B
1998, 57, 14690–14697.
[49] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77,
3865–3868.
7] R. Marx, Z. Naturforsch. 1995, 50b, 1061–1066.
8] R. Marx, J. Solid State Chem. 1997, 128, 241–246.
9] R. Marx, H. M. Mayer, Z. Naturforsch. 1995, 50b, 1353–1358.
10] R. Marx, H. M. Mayer, J. Solid State Chem. 1997, 130, 90–96.
11] R. Marx, R. M. Ibberson, J. Alloys Compd. 1997, 261, 123–131.
12] R. Marx, H. M. Mayer, Z. Naturforsch. 1996, 51b, 525–530.
13] R. Marx, J. Alloys Compd. 1997, 256, 196–206.
14] R. Marx, Z. Anorg. Allg. Chem. 1997, 623, 1912–1916.
15] R. Marx, Eur. J. Solid State Inorg. Chem. 1998, 35, 197–209.
16] A. Rabenau, H. Schulz, J. Less-Common Met. 1976, 50, 155–159.
17] R. Marx, Habilitation Thesis, Freie Universität Berlin, 2002.
18] R. Marx, F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 2006,
Received: January 4, 2010
Published Online: March 31, 2010
632, 2151.
9
46
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