Synthesis, structure, and properties of scandium dysprosium antimonide ScDySb

Article abstract of DOI:10.1002/zaac.201000095

Scandium dysprosium antimonide ScDySb was synthesized from scandium metal and DySb in an all-solid state reaction at 1770 K. According to X-ray analysis of the crystal structure [P4/nmm, Z = 4, a = 430.78(1) pm, c = 816.43(4) pm, R₁ = 0.0238, wR(all) = 0.0688, 268 independent reflections], ScDySb adopts the anti-PbFCl type of structure, but with pronounced deviations in structural details, which are related to specific bonding interactions between the atoms involved. ScDySb shows antiferromagnetic ordering below 35.4 K, which was verified by susceptibility, heat capacity, and resistivity measurements. X-ray structure determination, performed at 30 K, showed no significant structural changes to occur during the magnetic phase transition. The band structure was calculated in the framework of Density Functional Theory. The bonding properties are comparable to those of Sc₂Sb. Pronounced basins of the Electron Localization Function (ELF) appear in the tetragonal pyramidal Sc₄Dy voids.

Full text of DOI:10.1002/zaac.201000095

ARTICLE
DOI: 10.1002/zaac.201000095
Synthesis, Structure, and Properties of Scandium Dysprosium Antimonide
ScDySb
[a]
[a]
[a]
Jürgen Nuss, Ulrich Wedig, and Martin Jansen*
Dedicated to Professor Rüdiger Kniep on the Occasion of His 65th Birthday
Keywords: Ternary pnictides; Metal-metal interactions; Magnetic properties; ELF (Electron Localization Function);
Density functional calculations
Abstract. Scandium dysprosium antimonide ScDySb was synthesized which was verified by susceptibility, heat capacity, and resistivity
from scandium metal and DySb in an all-solid state reaction at 1770 K. measurements. X-ray structure determination, performed at 30 K,
According to X-ray analysis of the crystal structure [P4/nmm, Z = 4, showed no significant structural changes to occur during the magnetic
a = 430.78(1) pm, c = 816.43(4) pm, R
68 independent reflections], ScDySb adopts the anti-PbFCl type of of Density Functional Theory. The bonding properties are comparable
structure, but with pronounced deviations in structural details, which to those of Sc Sb. Pronounced basins of the Electron Localization
1
= 0.0238, wR(all) = 0.0688, phase transition. The band structure was calculated in the framework
2
2
are related to specific bonding interactions between the atoms in- Function (ELF) appear in the tetragonal pyramidal Sc
4
Dy voids.
volved. ScDySb shows antiferromagnetic ordering below 35.4 K,
Introduction
tetragonal crystal system and the ratio of the two free atomic
parameters (zPb and zCl for PbFCl). Recently, we have pre-
sented a structure map, which allows for identifying ionic, co-
valent, and metallic bonding regions among all the (anti)
PbFCl type representatives [9, 10].
The PbFCl type of structure is preferably and most fre-
quently formed by ionic compounds with the formula MXY.
Usually a large cation M, and two anions X and Y, which differ
in size significantly, are the constituents needed. Representa-
tive members are fluoride- [1], oxide- [2, 3], hydride- [4], and
nitride-halides [5]. However, if different kinds of interactions,
like covalent or metallic bonding gain more importance, con-
siderations based on a simple hard sphere model are no longer
appropriate for respective compounds with this structure type.
Numberless examples of the same atomic arrangement with
partial covalent or metallic bonding have been reported.
Among them are ZrSiS [6, 7] or NbSiAs [8], and also interme-
Sc Sb [11] was the first example showing the general topol-
2
ogy of PbFCl where pronounced basins of the Electron Locali-
zation Function (ELF) were found in the square pyramidal
voids [10]. Since such structural and electronic features can be
regarded a prerequisite for interesting phenomena, we are
looking for further compounds with the same phenotype.
Herein we report on synthesis and characterization of a new
representative ScDySb, which is the only representative in the
series ScRESb (RE = rare earth metal) that crystallizes in the
PbFCl type of structure, known up to now. The other members
tallic phases of general formula A B (A1A2B). In the latter
2
case, one (A), or two different metals (A1, A2) occupy the sites
of F and Cl in PbFCl, whereas a metalloid (B), which is often
a heavy element of group 14 or 15, substitutes for lead. Some
interesting representatives of such anti-PbFCl type structures
are: Cu Sb [9], Fe As [10], Sc Sb [11], LiFeAs [12, 13],
(
RE = La, Ce, Pr, Nd, Sm, Tb) all adopt the La Sb structure
2
type [17].
2
2
2
Results and Discussion
TiREGe (RE = Y, Gd–Tm) [14].
Starting from binary DySb and scandium metal, the com-
pound ScDySb was synthesized by all-solid state reaction as a
silver grey regulus in gram amounts, and as a single phase
product.
All in all, about 990 compounds are referred to crystallize in
the PbFCl (anti-PbFCl) type of structure [15, 16]. The struc-
tural variations caused by varying bonding principles can be
fully addressed by only two parameters, the c/a ratio of the
*
Prof. Dr. M Jansen
Physical Properties
Fax: +49-711-689-1502
E-Mail: M.Jansen@fkf.mpg.de
The temperature variation of the magnetic susceptibility,
χ(T), shows Curie–Weiss behavior at higher temperatures
(200–330 K, Figure 1). Data analysis result in an effective
[
a] Max-Planck-Institut für Festkörperforschung
Heisenbergstr. 1
70569 Stuttgart, Germany
Z. Anorg. Allg. Chem. 2010, 636, 913–918
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
913

J. Nuss, U. Wedig, M. Jansen
ARTICLE
magnetic moment (μ ) of 10.75 μ , which is very close to the
eff
B
6
expectation value for the H
ground state configuration of
5/2
1
3
+
the Dy ion (10.65 μ ) and a Curie–Weiss temperature θ of
B
w
+
32 K. The positive θ value indicates ferromagnetic interac-
w
tion to dominate at higher temperatures, whereas antiferromag-
netic ordering occurs at T = 35 K (Figure 1).
N
Figure 3. Heat capacity of SyDySb between 2 and 100 K.
changes is not atypical, as can be seen using the example of
the antiferromagnetic transition of isotypic TiTbSi [14, 18],
where neutron diffraction studies [18] indicate that the mag-
netic structure consists of ferromagnetic terbium double layers,
which are antiferromagnetically coupled along the c axis, a
picture, which seems to be consistent with the magnetic prop-
erties of ScDySb as well.
Figure 1. Susceptibility and inverse susceptibility of ScDySb versus
temperature.
The specific resistivity, ρ(T), of ScDySb drops almost line-
arly between 295 K (1.25 mΩ·cm) and 50 K (0.87 mΩ·cm),
which corresponds to a typical metallic behavior. Near 35 K,
Table 1. Crystal data, data collection, and refinement details for
the resistivity exhibits an anomaly, which is due to the onset ScDySb.
of the magnetic ordering (Figure 2).
Temperature /K
296.0(2)
30.0(2)
Formula weight
329.21
Space group (no.), Z
P4/nmm (129), 2
Lattice constants /pm a = 430.78(1)
c = 816.43(4)
429.99(7)
812.94(14)
1.891
c/a = 1.895
151.51(1)
7.216
0.040 × 0.025 × 0.015
SMART APEX II, Bruker AXS
0.71073
V /Å3
151.31(4)
7.274
ρ
xray /g·cm–3
Crystal size
Diffractometer
X-ray radiation, λ /Å
Absorption correction multi-scan, SADABS [29]
2
θ range /°
4.98 ≤ 2θ ≤ 74.34
–7 ≤ h ≤ 7,
Index range
–
7 ≤ k ≤ 7,
–
13 ≤ l ≤ 13
Reflection collected
Data, Rint
3991
268, 0.020
10
3747
268, 0.032
Figure 2. Electric resistivity versus temperature of ScDySb, between
No. of parameters
5
and 295 K.
Transmision: tmax, tmin 0.621, 0.334
0.619, 0.332
0.0252
2
2
R
1
[F > 2σ(F )]
0.0238
0.0688
2
wR(F )
0.0722
Temperature dependence of the heat capacities, C (T), of
p
Extinction coefficient 0.0063(16)
0.0063(18)
CSD-421440
ScDySb in applied fields of 0 and 7 T are presented in Fig-
ure 3. A sharp peak is observed in zero-field heat capacity at
Deposition no. [32]
CSD-421439
3
5.4 K, which coincides with the antiferromagnetic ordering
temperature of the compound.
In order to verify whether the magnetic ordering at 35.4 K
is accompanied by a structural phase transition, single crystals
were measured at room temperature and 30 K (Table 1, Ta-
Crystal Structure
According to a single-crystal X-ray diffraction analysis,
ble 2, and Table 3). No significant structural changes were ob- ScDySb crystallizes in the tetragonal anti-PbFCl type of struc-
served at low temperatures, except for a decrease of lattice ture (space group P4/nmm, Pearson code tP6, Wyckoff se-
constants and displacement parameters, which is a result of the quence c2a), with dysprosium and antimony occupying the
reduced thermal motion. The absence of structural chemical two 2c sites (¼, ¼, z), whereas scandium is located on the
9
14
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Z. Anorg. Allg. Chem. 2010, 913–918

Scandium Dysprosium Antimonide ScDySb
Table 2. Atomic coordinates and displacement parameters Uij /pm for ScDySb at 30 and 296 K (U12 = U13 = U23 = 0).
2
Atom
Dy
Site
x
y
z
U
11 = U22
U
33
U
eq
T /K
2c
¼
¼
0.35035(6)
94(2)
45(3)
86(2)
43(2)
68(4)
102(2)
62(2)
120(3)
75(3)
41(6)
4(6)
97(2)
50(2)
98(2)
54(2)
58(3)
17(3)
296
30
0
.34991(6)
Sb
Sc
2c
2a
¼
¾
¼
¼
0.73097(9)
296
30
0
0
.73101(9)
296
30
23(4)
Table 3. Interatomic distances /pm in ScDySb at 30 and 296 K.
feature of PbFCl (Figure 4b). The nearest neighbors of dyspro-
sium are five antimony atoms arranged at the corners of a
square pyramid, thus forming NaCl type fragments, which are
Atomic contact
distance 296 K
310.8(1)
30 K
mult.
Dy
Sb
Sc
–Sb
309.8(1)
1
4
4
1
4
4
4
4
4
also present in La Sb and related structures [17, 19, 20].
3
11.76(2)
311.08(5)
356.56(6)
309.8(1)
2
–
Sc
358.06(4)
310.8(1)
ScDySb is a shear variant of the tI12 structure type of La
2
Sb
–Dy
(
shear vector ½ ½ 0). The much shorter d(Sc–Sc) distance of
311.76(2)
311.08(5)
306.66(6)
356.56(6)
306.66(6)
304.05(5)
3
04.51(1) pm in comparison to d(Sc–Dy) = 358.06(4) pm, in
–
Sc
307.63(6)
358.06(4)
307.63(6)
304.61(1)
the non-capped square of the SbDy Sc polyhedra, indicate ad-
5
4
–Dy
4
ditional Sc–Sc interactions in the 4 nets of scandium (see Fig-
ure 4a). The distances d(Sc–Sc) are the shortest distances in
the structure, shorter than d(Sc–Sb) = 307.63(6) pm, and even
shorter than in metallic scandium (321.2 pm). Similar struc-
–
–
Sb
Sc
tural relationships are found in Sc Sb [11]. Thus ScDySb can
2
special position 2a (¾, ¼, 0) (cf. Table 1, Table 2, and Ta-
4
be regarded as a layered structure with alternating Sc 4 nets
ble 3).
and rock-salt like double layers of DySb [9, 10] (see Fig-
ure 4a).
The
strongly
bonded
hetero-atomic
framework
3
[SbDy5/5Sc4/4] is formed by condensed SbDy Sc monocaped
∞
5
4
The structural relationships of all PbFCl type representatives
can be described illustratively by plotting the ratio of the site
parameters q = z /(1–z ) against the c/a ratio (p), with A2 =
square antiprisms [d(Sb–Dy) = 310.8(1) pm (× 1), d(Sb–Dy) =
11.76(2) pm (× 4), d(Sb–Sc) = 307.63(6) pm (× 4), cf. Ta-
ble 3 and Figure 4a], which, of course, is also a distinguished
3
A2
B
Dy and B = Sb for example ScDySb (see Figure 5). At the
first glance, this choice of coordinates for a structural field
diagram seems to be rather arbitrary, but the representation
allows to distinguish the interactions between A1–B, A2–B, and
A1–A2 (q) in comparison to the A1–A1 interactions, the latter
ones being represented by c/a (p). Of course, this works only
when the crystallographic origin and the crystallographic sites
of the respective atoms correspond. This is described in detail
Figure 5. Structure map, showing selected A
Figure 4. Perspective representation of the crystal structures of a) ScDySb tion zA2/(1–z ) = f(c/a) visualizes the structural distortion (data from
and b) PbFCl. The margins of the unit cell are shown in green [37]. [9–11, 16]).
2
B compounds. The func-
B
Z. Anorg. Allg. Chem. 2010, 913–918
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915

J. Nuss, U. Wedig, M. Jansen
ARTICLE
in references [9] and [10]. As expected, ScDySb can be found differences are rather small, assuming a magnetic ordering as
in the same region of the structure field as Sc Sb, showing the found in TiTbSi [18] appears reasonable.
2
same structural relations as described above (Figure 5).
The substitution of Sc2 in Sc Sb by dysprosium leads to an
2
increase of the unit cell volume by 9.3 %. According to the
results of the topological analysis of the computed electron
density, this is due to the dysprosium atomic basin, which is
Electronic Structure
The band structure calculations reveal the similarity of the by 27.9 % larger than the corresponding Sc2 basin. The scan-
electronic structures of ScDySb and Sc Sb. Disregarding the dium (Sc1) and the antimony basins are expanded by only
2
Dy 4f bands, the densities of states (DOS) and their atom- and 4.4 % and 2.6 % respectively. The variation of the charges in
l-dependent projections show the same features (cf. [10] and the basins is in the order of only 0.1 electrons. The more pro-
Figure 6). Rather broad bands with mainly Sb 5p character nounced buckling of the double layers and the enhanced c/a
start at 1.2 eV below the Fermi level (E ). These are separated ratio in ScDySb and thus the slight different position in the
F
from the bands around E , which show the character of the structure map (Figure 5), as compared to Sc Sb, seems to have
F
2
scandium and dysprosium valence orbitals. Remarkable are primarily no electronic origin, but is due to the space require-
very narrow bands at –0.7 eV. Like in Sc Sb they can be pulled ments of the dysprosium atom.
2
together with the interstitial localization pattern discussed be-
The expansion of the unit cell leads to a slight shrinkage
3
3
low. The only significant difference between the band struc- (10.5 Å versus 10.7 Å in Sc Sb) of that basin of the Electron
2
tures of the two compounds is the spin polarization in ScDySb Localization Function (ELF, [21]), which is situated in the te-
originating from the partially filled 4f shell of dysprosium. The tragonal pyramidal voids enclosed by four scandium and one
integrated spin density within the dysprosium atomic sphere dysprosium atoms (Figure 7). The integrated valence electron
amounts to 4.6 electrons. This is consistent with a hextet Dy3+ density within this basin amounts to 1.2 electrons. Careful
ground state as deduced from the magnetic measurements. The analysis of the final difference Fourier map gave no evidence
spin polarization on the other atomic sites is negligible. A fer- for an interstitial atom in these Sc Dy cavities, which one
4
romagnetic ordering within the DySb double layers is by might expect to be present in analogy to previous instances
–
1
1
0 kJ·mol more stable than an antiferromagnetic one. Coup- when overlooked interstitial atoms were identified by localiza-
ling adjacent ferromagnetic double layers antiferromagneti- tion patterns [22]. Such stuffed intermetallics are known how-
cally leads to a further gain of 2 kJ·mol . Although the energy ever, in the series RE Sb O (RE = La, Ce, Pr, Sm, Tb, Dy)
–1
9
5
5
[23–25], where oxygen occupies corresponding voids in this
Figure 6. Total (grey area) and projected densities of states (see leg- Figure 7. Domains of the Electron Localization Function (ELF, η =
end) of the majority spin component of ScDySb. The Fermi level (E
F
)
0.5) in ScDySb, a) perspective representation of the crystal structure,
b) Sc-layer perpendicular to the c axis.
is shifted to 0 eV.
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Z. Anorg. Allg. Chem. 2010, 913–918

Scandium Dysprosium Antimonide ScDySb
α
type of structure, which can also be regarded as a stuffed defect many) with graphite-monochromated Mo-K radiation, equipped with
a N-Helix low temperature device [Oxford Cryosystems, Oxford,
United Kingdom (28–300 K)] [28]. The reflection intensities were in-
tegrated with the SAINT subprogram in the Bruker Suite software
package [29], a multi-scan absorption correction was applied using
SADABS [30]. The structures were solved by direct methods and re-
fined by full-matrix least-squares fitting with the SHELXTL software
package [31]. Experimental details are given in Table 1 and Table 2.
Further details may be obtained from the Fachinformationszentrum
Karlsruhe [32].
variant of Sc Sb [23] and therefore of ScDySb, too:
2
[
Dy Sb ][Sc  ] a [RE Sb ][RE O ].
5 5 5 5 5 5 4 5
Conclusions and Outlook
Based on a thorough analysis of ScDySb, we claim that the
localization pattern found in the voids is an intrinsic property
of the ELF topology in this intermetallic compound, indicating
a multi center interaction between the metal atoms. ScDySb
is a further example showing this pronounced topology, and
confirms the feature previously reported for Sc Sb [10]. This Band Structure Calculations
2
special relation is also reflected by the position of both com-
pounds in the discussed structure field diagram (Figure 5).
Scalar relativistic density functional calculations (DFT) were per-
formed with the TB-LMTO-ASA program [33], applying the local spin
The structure of ScDySb, and also the structure of other anti- density approximation (LSDA) to allow for spin polarization. The local
PbFCl representatives, show atomic arrangements, which are exchange-correlation functional of von Barth and Hedin [34] was used.
closely related to the La Sb type of structure. Both can be The Kohn–Sham eigenvalues were computed at 140 irreducible k-
2
points in the Brillouin zone. In addition to the atomic spheres, empty
spheres were added at Wyckoff position 2b (¼ ¾ ½) in order to enable
the neglect of the interstitial region and to reduce the overlap of the
atomic spheres. Supercells (2a × b × c and a × b × 2c) were consid-
ered to investigate the spin ordering.
transferred into each other by a virtual shearing (shear vector
½ 0), whereby the most pronounced structural changes are
½
affected to the pyramidal voids, which change into octahedral
ones in the case of La Sb. A stuffed variant, e.g. Eu Sb O
2
4
2
[19], is known, where these voids are occupied by oxygen.
An analogue stuffed variant of Sc Sb type compounds is still The Electron Localization Function (ELF), derived from the Pauli ki-
2
missing. It is amazing, that all the other representatives netic energy density [21], was computed as an indicator for local elec-
ScRESb with larger rare earth elements (RE = La, Ce, Pr, Nd, tronic substructures like core shells, covalent bonds and lone pairs.
Both, the total electron density and the ELF were investigated by a
Sm, Tb) are known to adopt the La Sb type of structure [17].
2
topological analysis [35, 36], separating the whole space into atomic
or localization basins. The charges within these basins were computed
The relationship between “empty” and “filled” La Sb type
2
compounds and their differences in the electronic properties
by integrating the valence electron density, being available in a regular
will be discussed somewhere else [26].
mesh with a grid distance of 7 pm.
Experimental Section
Synthesis
Acknowledgement
The authors gratefully acknowledge the help of Mrs. S. Prill-Diemer
ScDySb was synthesized in ≈ 1 g batches from DySb and scandium
metal (ChemPur, Karlsruhe, Germany). The binary dysprosium anti-
monide was prepared from the elements in a sealed tantalum ampoule
at 1120 K for 36 h. In order to remove potential impurities of hydro-
for carrying out the synthesis, Mrs. E. Brücher for susceptibility meas-
urements, and Mrs. G. Siegle for resistivity and heat capacity measure-
ments. This work was supported by the Deutsche Forschungsgemein-
schaft (DFG) within the priority program Experimental charge density
–
4
gen, the reaction was done in dynamic vacuum (10 mbar). Stoichio-
metric amounts of the starting materials were mixed and sealed in a
tantalum ampoule. The following temperature profile was applied: 298
as the key to understand chemical interaction (SPP1178).
–
1
→
(
1770 K (50 K·h , subsequent annealing for 36 h); 1770 → 1520 K
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J. Nuss, U. Wedig, M. Jansen
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