A new polymorph of potassium chromate(III), β-KCrO2, and reinvestigation of α-KCrO2

Article abstract of DOI:10.1002/zaac.201200476

α-KCrO₂ was synthesized by the azide/nitrate route. Stoichiometric mixtures of the precursors (KN₃, KNO₃, and Cr₂O₃) were heated in a special regime up to 853 K and annealed at this temperature for 5 h in a specially designed silver container. Dark green single crystals of β-KCrO₂ were grown by post annealing the reaction product at 773 K for 200 h in silver crucibles. According to single-crystal X-ray analysis, the new high temperature modification, β-KCrO₂, crystallizes in the β-RbScO₂ type of structure [P6₃/mmc; a = 3.0427(4) A, c = 11.924(2) A; c/a = 3.918; Z = 2]. The characteristic feature of the structure are CdCl ₂ analogue slabs of [CrO_6/3]^- edge shared octahedra stacked along the [001] direction with K⁺ atoms incorporated between the layers in a trigonal prismatic arrangement, rare for lighter alkali atoms. We have reinvestigated the specific heat (from 2 to 300 K) and the magnetic susceptibility (2 to 350 K) on α-KCrO₂, and clearly identified in the specific heat measurements, a λ-type anomaly at 23 K, indicating the onset of long-range AFM ordering. The Curie-Weiss fit of experimental data in the temperature range above 100 K, yields the negative Curie-Weiss temperature of -220 K, indicating predominant antiferromagnetic spin-exchange interaction, with an effective magnetic moment (μ_eff) of the order of 3.91 μ_B, corresponding to a g-factor [μ_eff/μ_B = g[S(S+1)]^1/2] of 2.019 well in accordance for Cr³⁺ (d³ system) with spin S = 3/2. Copyright

Full text of DOI:10.1002/zaac.201200476

ARTICLE
DOI: 10.1002/zaac.201200476
A New Polymorph of Potassium Chromate(III), β-KCrO , and
2
Reinvestigation of α-KCrO2
[a]
[a]
[a]
Naveed Zafar Ali, Jürgen Nuss, and Martin Jansen*
Dedicated to Professor Hartmut Bärnighausen on the Occasion of His 80th Birthday
Keywords: Azide/nitrate route; Potassium; Chromium oxides; Magnetic properties; Specific heat
Abstract. α-KCrO
chiometric mixtures of the precursors (KN
heated in a special regime up to 853 K and annealed at this temperature
for 5 h in a specially designed silver container. Dark green single crys-
2
was synthesized by the azide/nitrate route. Stoi-
, KNO , and Cr ) were atoms. We have reinvestigated the specific heat (from 2 to 300 K)
and the magnetic susceptibility (2 to 350 K) on α-KCrO , and clearly
identified in the specific heat measurements, a λ-type anomaly at 23 K,
the layers in a trigonal prismatic arrangement, rare for lighter alkali
3
3
2 3
O
2
tals of β-KCrO
2
were grown by post annealing the reaction product at indicating the onset of long-range AFM ordering. The Curie-Weiss fit
773 K for 200 h in silver crucibles. According to single-crystal X-ray of experimental data in the temperature range above 100 K, yields the
analysis, the new high temperature modification, β-KCrO
in the β-RbScO type of structure [P6 /mmc; a = 3.0427(4) Å, c =
1.924(2) Å; c/a = 3.918; Z = 2]. The characteristic feature of the
2
, crystallizes
negative Curie-Weiss temperature of –220 K, indicating predominant
antiferromagnetic spin-exchange interaction, with an effective mag-
2
3
1
netic moment (μeff) of the order of 3.91 μ
analogue slabs of [CrO6/3] edge shared octahedra g-factor [μeff /μ
= g[S(S+1)]1/2] of 2.019 well in accordance for Cr3+
stacked along the [001] direction with K atoms incorporated between (d system) with spin S = 3/2.
B
, corresponding to a
–
structure are CdCl
2
B
+
3
Introduction
thus might adopt the β-RbScO
structure. KCrO in the
2 2
[2]
α-NaFeO structure has been reported previously.
2
Two dimensional magnetic oxides with triangular lattices,
In this study, we present results on a new high temperature
also recognized as triangular lattice Heisenberg antiferromag- polymorph of KCrO , namely β-KCrO , which is built by
3+
2
2
nets (TLHAF),[ have been extensively studied because of the stacking well-separated, triangular planes of Cr with an oxy-
1]
frustrated magnetically exchange couplings expected and fre- gen ion stacking sequence of ABBAAB, bringing forward an
+
quently observed. The unusual ground states, along with its unusual trigonal prismatic coordination of the lighter K cat-
propensity to perturbations, make these geometrically frus- ion. In addition, we reinvestigate the specific heat and mag-
trated systems widely studied compounds. This holds also true netic susceptibility of its alpha analogue (α-KCrO2).
for ACrO (A = Li, Na, and K), a family of compounds that
2
crystallize in the α-NaFeO type of structure, wherein the al-
2
kali ions occupy the anti-prismatic arrangement embedded be- Results and Discussion
–
[2,3]
tween layers of edge sharing [CrO6/3] octahedra.
For com-
[
7–9]
α-KCrO was synthesized by the azide/nitrate route.
The
2
pounds of the family AMO (M = transition metal), with larger
2
+
green product is very sensitive to humid air. The atomic ratio
of the heavy elements was confirmed by scanning electron mi-
croscopy equipped with an integrated EDAX-EDX system to
be K:Cr = 1.02:1.00. Dark green single crystals of β-KCrO2
were grown by post annealing the reaction product at 773 K
for 200 h in silver crucibles.
A cations, also an alternative, the β-RbScO type of struc-
2
ture,[4–6]
+
with the A cation in a trigonal prismatic surrounding
has been observed. However, virtually nothing is known about
its relation to the α-NaFeO type with respect to phase sta-
2
bility. In particular, it is unclear whether the β-RbScO type
2
corresponds to a HT or HP modification of the ambient
α-NaFeO structure of a dimorphic compound of general for-
2
mula ABX . The 3d element next to scandium of similar size
and preference of the oxidation state (3+) is chromium, which
2
Crystal Structures
The polyhedral view of the crystal structures of both
α-KCrO and β-KCrO are shown in Figure 1. The new poly-
2
2
*
Prof. Dr. M. Jansen
Fax: +49-711-689-1502
E-Mail: M.Jansen@fkf.mpg.de
morph, β-KCrO
2
(Figure 1b) crystallizes in the β-RbScO type
2
of structure (Table 1 and Table 2). As a characteristic feature
of the structure, CdCl2 analogue layers of edge shared
[CrO6/3]– octahedra are stacked along the [001] direction with
[
a] Max-Planck-Institut für Festkörperforschung
Heisenbergstr. 1
70569 Stuttgart, Germany
Z. Anorg. Allg. Chem. 2013, 639, (2), 241–245
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
241

N. Z. Ali, J. Nuss, M. Jansen
Table 3. Interatomic distances /Å and angles /° in β-KCrO at 298 K.
ARTICLE
2
Atomic contact
Distance, angle
Mult.
Cr–O
K–O
O–Cr
O–K
2.033(1)
2.631(2)
2.033(1)
2.631(2)
6
6
3
3
O–Cr –O
O–K–O
180.0(1)
3
6
6
3
6
6
3
9
8
6.90(6)
3.10(6)
96.20(6)
1
7
40.99(2)
0.67(5)
Cr–O–Cr
96.90(6)
oxide anions with d(K–O) = 2.631(2) Å (Table 3). The O–Cr–
O angles of 83.10° and 96.90° indicate a pronounced compres-
Figure 1. Perspective representation of the crystal structure of (a) α- sion of the CrO octahedron along one of its threefold axes,
6
2 2
KCrO and (b) β-KCrO . Color code: potassium (green spheres), chro-
corresponding to the c direction of the crystal structure.
The Cr–Cr intralayer distances within the edge shared coor-
dination octahedra are d(Cr–Cr) = 3.0427Å (6ϫ), whereas
mium (blue spheres), oxygen (red spheres). Red and blue polyhedra
emphasize the different coordination environment: chromium (octahe-
dron), potassium (trigonal antiprism, left), potassium (trigonal prism,
right).
+
interlayer distances connected by K trigonal prisms amount to
d(Cr–Cr) = 5.962 Å, indicating the magnetically rather isolated
two-dimensional triangular planes of S = 3/2 Cr3+ ions.
The oxygen ion stacking sequence ABBAAB in β-KCrO2
results from the change of the anti-prismatic coordination
Table 1. Crystal data, data collection, and refinement details for β-
KCrO at 298 K.
2
+
2–
Formula weight
Space group (no.), Z
Lattice constants /Å
123.10
P6 /mmc (194), 2
a = 3.0427(4)
c = 11.924(2)
95.60(3)
4.276
mode of K within the cubic close arrangement of O anions
3
(stacking sequence: ABCABC) in α-KCrO to a prismatic one
2
in β-KCrO .The unit cell volumes for α- and β-KCrO at room
2
2
temperature are 143.6 Å3 and 95.60 Å , which correspond
[2]
3
V /Å3
3
3
xray /g·cm–3
to molar volumes of 47.86 Å and 47.80 Å per formula unit,
respectively. These differences of the α- and β-polymorph are
quite small virtually within the uncertainty of measurement. In
analogy, the densities 4.270 g·cm and 4.276 g·cm of both
polymorphs are equal, within errors. These findings are also
reflected by the thicknesses of the CrO6/3 and KO6/3 slabs,
which correspond to the heights of the respective polyhedra
along the c axis (Figure 1). The thicknesses of the CrO6/3 slabs
ρ
3
Crystal size /mm
Diffractometer
0.20ϫ0.10ϫ0.10
SMART APEX I, Bruker AXS
X-ray radiation, λ /Å
Absorption correction
Mo-K
α
, 0.71073
–3
–3
[
10]
Multi-scan, SADABS
6.84 Յ 2θ Յ 69.78
–4 Յ h Յ 4,
2θ range /°
Index range
–
–
4 Յ k Յ 4
19 Յ l Յ 18
Reflection collected
Data, Rint
1248
107, 0.037
8
0.512, 0.307
0.026
0.064
(dAB, see Figure 1) are 2.055 Å (α) and 2.045 Å (β), and those
of the KO6/3 slabs are dBC = 3.909 Å (α) and dBB = 3.917 Å
No. of parameters
Transmission: tmax, tmin
(β), respectively. Meaning, the compression of the CrO octa-
6
2
2
1
R [F Ͼ 2σ(F )]
hedra and the elongation of the KO trigonal prisms (or anti-
6
2
wR (F )
prisms) are similar in both polymorphs, and forced by the ne-
cessity to adapt the CrO6/3 partial structure to the KO6/3 partial
structure, with rigid d(Cr–O) = 2.03 Å and d(K–O) = 2.63 Å
Deposition no.[
11]
CSD-425293
distances. It is worth mentioning, that in case of the α- and β-
–
4 2
Table 2. Atomic coordinates and displacement parameters Uij /10 Å
for β-KCrO at 298 K (U11 = U22, U13 = U23 = 0, U12 = 1/2 U11).
[4,12]
polymorphs of RbScO similar observations can be made.
2
2
There is also no significant change in volume and density ob-
served, when the coordination polyhedra of rubidium changes
from a trigonal anti-prismatic to prismatic one.
Atom Site
x
y
z
U
11
U
33
U
eq
Cr
K
O
2b
2c
4f
0
0
0
1/4
82(3)
129(3) 110(4) 123(2)
75(8) 89(4)
75(3)
79(2)
MAPLE calculations[ were performed for both, α- and
13]
1/3 2/3
1/3 2/3
0.5858(2) 96(6)
β-KCrO . The closeness of the calculated lattice energies of
2
9
983.86 kJ·mol–1 for α-KCrO and 9995.95 kJ·mol for β-
–1
2
KCrO reflect the similarities of both polymorphs, discussed
K atoms sandwiched between the layers. The Cr cations above. The values agree well with the sums of the calculated
2
+
3+
occupy the octahedral interstices with d(Cr–O) = 2.033(1) Å, partial Madelung energies derived from respective binary ox-
+
–1
whereas K ions reside in a trigonal prismatic surrounding of ides (9971.56 kJ·mol ) with a deviation as small as 0.24%.
2
42 www.zaac.wiley-vch.de © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2013, 241–245

2 2
β-KCrO , and Reinvestigation of α-KCrO
Phase Transition
In 1977, Hoppe et al. reported on the α-RbScO modifica-
2
[12]
tion to crystallize in the α-NaFeO type of structure.
Pre-
2
viously another phase, β-RbScO occurring above 300 K was
2
discovered by the same group.[ However, no concrete evi-
dence was given of a true phase transition to occur between α-
RbScO and β-RbScO polymorphs. In much analogy, in the
4]
2
2
presented study, after ascertaining the new polymorph β-
KCrO by single crystal structure analysis, an attempt was
2
made to understand the relationship between the two poly-
morphs of KCrO2 by following the thermal evolution of
α-KCrO into the high temperature phase β-KCrO .
2
2
DTA and DSC measurements give no conclusive hint for
the phase transition from the α- into the β-phase. The Rietveld
fit of the phase pure α-KCrO sample used for this study and
for further physical properties measurements is shown in Fig-
ure 2. Figure 3 shows the X-ray diffraction patterns, measured (c), 100 h (d).
2
Figure 3. Scattered X-ray intensities (λ = 0.7093 Å) for polycrystalline
samples of KCrO annealed at 853 K for t = 5 h (a), 25 h (b), 50 h
2
from quenched samples of polycrystalline KCrO heated at
2
8
53 K for different annealing times t: a (t = 5 h), b (t = 25 h),
posed that KCrO would be a nice candidate to study 2D anti-
2
c (t = 50 h), and d (t = 100 h). The weight percentages of β-
KCrO in the samples were evidenced by quantitative multi-
component Rietveld analyses using the program TOPAS.[14]
They amount to 6% (a), 12% (b), 26% (c), and 35% (d) of
β-KCrO , respectively. When increasing the annealing time
above 100 h, a competing reaction, namely deintercalation of
potassium and formation of a potassium deficient phase
ferromagnetic coupling because of the large separation be-
tween the chromium planes as compared to the lithium and
2
[1]
sodium analogues.
The plot in Figure 4 displays the temperature dependent
magnetic susceptibility of a polycrystalline sample of α-
2
KCrO . The inverse magnetic susceptibility grows almost lin-
2
early with increasing temperature and is independent of the
K1–xCrO plays a major rule. Long-term annealing ends up in
reddish brown samples of K1–xCrO2.[
2
applied magnetic field above the Néel temperature (T ) at vari-
N
15]
ous applied magnetic fields. The data can be fitted complying
with the Curie-Weiss law (χmol = C/(T–θ) + χ ) with θ = Weiss
o
constant, and C = Curie constant. The temperature independent
term, χ = χ + χvv accounts for core electrons diamagnetic
o
dia
contributions (χ ) and van Vleck paramagnetic contributions
dia
(
χvv) for the Cr3+ ion. The diamagnetic susceptibility of the
core electrons can be estimated by summing up increments of
[
20]
3+
–6
3
–1
all the ions as tabulated,
(Cr : –11ϫ10 cm ·mol ,
+
–6
3
–1
2–
–6
3
–1
K : –13ϫ10 cm ·mol , 2O : –24ϫ10 cm ·mol ) re-
sulting in a total diamagnetic contribution of χ
48ϫ10–6 cm ·mol per formula unit. Whilst the van Vleck
=
dia
3
–1
–
2
Figure 2. Scattering X-ray intensities for α-KCrO . Shown are the ob-
served pattern, the best Rietveld fit profile, the difference curve be-
tween observed and calculated profile, and the reflection markers. The
wavelength is λ = 0.7093 Å. The higher angle part of the plot is en-
larged by a factor of four.
Physical Properties of α-KCrO2
The magnetic behavior of two-dimensional oxochromates of
the family ACrO (A = Na, Li, and K) has been extensively
2
Figure 4. Temperature dependence of the magnetic susceptibility (χ
and 1/χ vs. T) for α-KCrO . The solid line represents the fit of the
investigated previously using neutron, and magnetic suscep-
2
tibility measurements.[
16–19]
In a recent review, it was pro- data to the Curie-Weiss law.
Z. Anorg. Allg. Chem. 2013, 241–245
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
243

N. Z. Ali, J. Nuss, M. Jansen
ARTICLE
3
+
paramagnetic contribution per Cr
7
cation amounts to transformation. As another implication, annealing at higher
–
6
3
–1 [21]
3+
3
5ϫ10 cm ·mol .
expects a μeff in the range of 3.70–3.90 μB.[ The Curie-Weiss tassium deficient phases K1–xCrO2.
fit of the experimental data at the temperature between 100 K The magnetic susceptibility χT backed by specific heat mea-
Ͻ T Ͻ 300 K with χ = χ + χvv ≈ +27ϫ10 cm ·mol (per surements, indicates onset of long-range AFM ordering, with
For Cr (d system) with S = 3/2 one temperature results in deintercalation of potassium yielding po-
22]
[15]
–
6
3
–1
o
dia
3
+
Cr ), the negative Curie-Weiss temperature of –220 K results, the Néel temperature precisely determined to be 23 K. More-
indicating predominant antiferromagnetic spin-exchange inter- over, the system is found to be frustrated magnetic system
action, with an effective magnetic moment (μ ) of the order (θ/TN ≈ 8). In order to gain insight and for better perspective
eff
1/
of 3.91 μ corresponding to a g-factor [μ /μ = g[S(S+1)]
about the mechanism of the frustration, muon-spin resonance
B
eff
B
2
+
[26]
]
of 2.019. The Weiss constant (θ = –220 K), exhibits a value (μ SR) experiments are underway.
approximately 8 times larger than the ordering temperature
T ≈ 26 K, i.e. a high frustration index (θ/T ) giving an indica-
N
N
tion for a strongly frustrated magnetic system.[
23,24]
At tem- Experimental Section
peratures above 300 K, the inverse magnetic susceptibility data
exhibit slight divergence from linear behavior, which is quite
unusual and is subject of further investigation.
Synthesis: KCrO
KN , KNO
mium oxide was prepared by heating (NH
in a flow of oxygen at 923 K for 24 h, whereas KN
2
was prepared via the azide/nitrate route[7–9] using
3
3
(Aldrich, 99%), and Cr
2
O
3
as starting materials. Chro-
Cr (Aldrich, 99.5%)
was synthesized
The starting materials
were mixed in the ratio required according to Equation (1) and ground
4
)
2
2 7
O
The specific heat for α-KCrO was recorded in the tempera-
2
3
ture range of 2 to 300 K (Figure 5). In the low temperature
[27]
3
from aqueous HN and cesium carbonate.
region one can see a λ-type anomaly at 23 K in the C (T)
P
5
curve, which we assign to the onset of long-range AFM order- in a ball mill, pressed in pellets (Ø = 13 mm) under 10 N, dried in a
ing well in accordance with the χ(T) plot. To probe the nature vacuum (10 mbar) at 423 K for 12 h and placed under argon in a
of the specific heat anomaly at TN in more detail, we also
–
3
tightly closed steel vessel provided with a silver inlay. In a flow of
dry argon, the following temperature profile was applied: 25Ǟ533 K
plotted C /T vs. T as shown in Figure 5, allowing to precisely
P
–
1
–1
–1
(
100 K·h ); 533Ǟ653 K (5 K·h ), 653Ǟ853 K (20 K·h ) with sub-
determine the Néel temperature to be 23 K. Upon examining
sequent annealing for 5 h at 853 K and later quenching to room tem-
perature.
the C /T vs. T plot in the temperature range 12 Ͻ T Ͻ 58 K,
P
the total entropy related to the magnetic order in KCrO was
2
–
1
–1
extracted to amount to 11.98 J·mol ·K (Smag), consistent
with the expected value R·ln(2S+1) = 11.53 J·mol ·K , where
5KN
3
+ KNO
3
+ 3Cr
2
O
3
Ǟ 6KCrO
2
+ 8N
2
Ȇ
(1)
–
1
–1
3
+ [25]
R is the gas constant and S = 3/2 for Cr .
Hazards: Rapid heating or running the reaction in a gas tight welded
container can lead to a dangerous explosion!
2
The obtained green α-KCrO powder, being extremely sensitive to hu-
mid air, was sealed in glass ampoules in an argon atmosphere and all
following manipulations with the substances were performed in inert
atmospheres of purified argon. Single crystals of β-KCrO
by subsequent annealing of the pressed pellet of reaction product at
73 K for 200 h in silver crucibles, which were sealed in glass am-
2
were grown
7
poules under dried argon.
Chemical Analysis: The atom ratio of the heavy elements was con-
firmed to be K:Cr = 1.02:1.00 with a scanning electron microscope
(
XL 30 TMP, Philips, Holland, tungsten electrode, 25 kV), equipped
with an integrated EDAX–EDX system (S-UTW-Si(Li) detector).
Structure Determination: Dark green single crystals of β-KCrO
2
were singled out and picked in a dry box in an argon atmosphere (O
2
,
2
H O Ͻ 0.1 ppm, M. Braun GmbH, Garching, Germany) and finally
mounted in a sealed glass capillary. Diffraction intensities were col-
lected with a SMART APEX I diffractometer (Bruker AXS, Karlsruhe,
P P
Figure 5. The plot of specific heat (C ) and C /T at zero field as a
function of T of polycrystalline sample of α-KCrO
2
.
α
Germany) equipped with a SMART-CCD (APEX), using Mo-K radia-
tion (λ = 0.71073 Å), at room temperature (298 K). The collection
Conclusions
and reduction of data were carried out with the Bruker Suite software
[
28]
package.
Intensities were corrected for absorption effects applying
Dark green crystals of β-KCrO , adopting the β-RbScO2
type of structure, were grown by post annealing the primary
product obtained along the azide/nitrate route. The new β-
2
[
10]
a multi-scan method. The structural data were refined by full-matrix
least-squares fitting with the SHELXTL software package,[ within
29]
3
the space groups P6 /mmc (194), whereby the atomic coordinates of
KCrO phase is found to be stable at high temperatures. The
[4]
2
β-RbScO2 were used as starting values. Details of crystallographic
¯
phase transformation from low temperature α-KCrO (R3m) to
2
data and data collection are given in Table 1, atomic coordinates and
high temperature β-KCrO (P6 /mmc) is found to be kinet- displacement parameters along with the selected interatomic distances
2
3
ically slow, and we were unable to achieve complete phase and angles for β-KCrO
2
are listed in Table 2 and Table 3, respectively.
2
44 www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 241–245

2 2
β-KCrO , and Reinvestigation of α-KCrO
Powder X-ray Analysis and Refinement: The X-ray investigation on [10] G. M. Sheldrick, SADABS, Bruker AXS Area Detector Scaling
and Absorption, Version 2008/1, University of Göttingen, Ger-
many, 2008.
powder samples was performed with a D8-Advance laboratory dif-
fractometer (Bruker AXS, Karlsruhe, Germany) with Mo-Kα1 radiation
[
11] Further details of the crystal structure investigations may be ob-
tained from the Fachinformationszentrum Karlsruhe, 76344 Egg-
enstein-Leopoldshafen, Germany (Fax: +49-7247-808-666;
E-Mail: crysdata@fiz-karlsruhe.de, http://www.fiz-karlsruhe.de/
request for deposited data.html) on quoting the depository number
CSD-425293.
(λ = 0.709300 Å) using a Våntag-1 position-sensitive detector (6°
opening angle) and a curved germanium monochromator. The powder
diffraction data were collected in the 2θ range of 4–50° on a sample
sealed in 0.3 mm glass capillary (Hilgenberg) kept rotating during data
collection for better particle statistics. For structure refinements (Riet-
[
14]
veld method), the software Topas 4.1 (Bruker AXS) was employed.
[12] H. Wiench, G. Brachtel, R. Hoppe, Z. Anorg. Allg. Chem. 1977,
436, 169.
Physical Properties: Temperature dependence of the specific heat (C
of a polycrystalline sample of α-KCrO was measured between 2 and
00 K with a commercial PPMS (Physical Property Measurement Sys-
tem, Quantum Design, 6325 Lusk Boulevard, San Diego, CA.) em-
p
)
[13] a) R. Hoppe, Angew. Chem. Int. Ed. Engl. 1966, 5, 95; b) R.
Hoppe, Angew. Chem. Int. Ed. Engl. 1970, 9, 25; c) D. Quane, J.
Chem. Educ. 1970, 47, 397; d) R. Huebenthal, MAPLE, Program
for the Calculation of the Madelung Part of Lattice Energy, Uni-
versity of Giessen, Germany, 1993; e) R. P. Grosso Jr., J. T. Ferm-
ann, W. J. Vining, J. Chem. Educ. 2001, 78, 1198.
2
3
[
30,31]
ploying the relaxation method.
To thermally fix the sample tablet
(Ø = 5 mm and thickness 1 mm) to the sapphire sample platform, a
[
[
14] A. A. Coelho, J. Appl. Crystallogr. 2003, 36, 86.
15] C. Delmas, M. Devalette, C. Fouassier, P. Hagenmuller, Mater.
Res. Bull. 1975, 10, 393.
minute amount of Apiezon-N vacuum grease was used. The heat ca-
pacity of the sample holder platform and grease was individually deter-
mined in a separate run and subtracted from the total measured heat
capacities.
[16] C. Delmas, G. Le Flem, C. Fouassierm, P. Hagenmuller, J. Phys.
Chem. Solids 1978, 39, 55.
[
[
[
[
17] C. Delmas, F. Menil, G. Le Flem, C. Fouassier, P. Hagenmuller,
J. Phys. Chem. Solids 1978, 39, 51.
18] J. L. Soubeyroux, D. Fruchart, C. Delmas, G. Le Flem, J. Magnet-
ism Magn. Mater. 1979, 14, 159.
19] J. L. Soubeyroux, D. Fruchart, J. C. Marmeggi, W. J. Fitzgerald,
C. Delmas, G. Le Flem, Phys. Status Solidi 1981, 67, 633.
20] a) H. Lueken, Magnetochemie, Teubner, Stuttgart, 1999; b) T. R.
McGuire, J. E. Scott, F. H. Grannis, Phys. Rev. 1956, 102, 1000.
Magnetic susceptibility χ(T) of a 54.7 mg powder sample of α-KCrO
2
was recorded in the temperature range from 2 to 350 K in external
magnetic fields ranging up to 7 T with a MPMS-XL7 SQUID magne-
tometer (Quantum Design, 6325 Lusk Boulevard, San Diego). The
moisture sensitive powder sample was filled in a dried SUPRASIL
glass tube (Ø = 4 mm) flushed with ca. 1 bar helium gas in order to
provide adequate thermal contact to the cryostat. The raw data obtained [21] a) T. A. Hewston, B. L. Chamberland, J. Magnetism Magn. Mater.
[
20]
was finally corrected for the core electron diamagnetic and potential
1984, 43, 89; b) J. Benkowitsch, H. Winter, Phys. Scripta. 1985,
31, 222; c) I. L. Shukaev, V. V. Butova, Inorg. Chem. 2012, 51,
van Vleck paramagnetic contribution (χVV) for the Cr3+ ion.
[21]
4931.
[
22] S. E. Dutton, E. Climent-Pascual, P. W. Stephens, J. P. Hodges,
A. Huq, C. L. Broholm, R. J. Cava, J. Phys. Condens. Matter
Acknowledgements
2011, 23, 246005.
[
[
[
23] P. Ramirez, Annu. Rev. Mater. Sci. 1994, 24, 453.
24] L. J. de Jongh, A. R. Miedema, Adv. Phys. 2001, 50, 947.
25] L. K. Alexander, N. Buettgen, R. Nath, A. V. Mahajan, A. Loidl,
Phys. Rev. B 2007, 76, 064429.
We thank Mrs. E. Brücher and Mrs. G. Siegle for carrying out the
magnetic susceptibility and specific heat measurements.
[
26] N. Z. Ali, M. Jansen, Paper in Progress.
References
[27] a) G. Brauer, Handbuch der Präparativen Anorganischen Chemie,
st ed., F. Enke Verlag, Stuttgart, 1975, p. 457; b) H. D. Fair, R. F.
1
[
1] A. Olariu, P. Mendels, F. Bert, L. K. Alexander, A. V. Mahajan,
A. D. Hillier, A. Amato, Phys. Rev. B 2009, 79, 224401.
2] W. Scheld, R. Hoppe, Z. Anorg. Allg. Chem. 1989, 568, 151.
3] J. L. Soubeyroux, D. Fruchart, J. C. Marmeggi, W. J. Fitzgerald, [28] Bruker Suite, version 2008/3, Bruker AXS Inc., Madison, WI,
C. Delmas, G. Le Flem, Phys. Stat. Solidi A 1981, 67, 633.
4] R. Hoppe, H. Sabrowsky, Z. Anorg. Allg. Chem. 1965, 339, 144.
Walker, Energetic Materials, Physics and Chemistry of Inorganic
Azides, Plenium Press, New York and London, vol. 1, 1977, p.
30.
[
[
USA, 2008.
[
[
[
[
[29] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
5] B. Deng, J. A. Ibers, Acta Crystallogr., Sect. E 2005, 61, i15-i17. [30] R. Bachmann, F. J. DiSalvo Jr., T. H. Geballe, R. L. Greene, R. E.
6] J. M. Babo, Th. Schleid, Z. Anorg. Allg. Chem. 2009, 635, 1.
7] D. Trinschek, M. Jansen, Angew. Chem. 1999, 111, 234; Angew.
Chem. Int. Ed. 1999, 38, 133.
Howard, C. N. King, H. C. Kirsch, K. N. Lee, R. E. Schwall,
H. U. Thomas, R. B. Zubeck, Rev. Sci. Instrum. 1972, 43, 205.
[31] J. S. Hwang, K. J. Lin, C. Tien, Rev. Sci. Instrum. 1997, 68, 94.
[
[
8] M. Sofin, E. M. Peters, M. Jansen, Z. Anorg. Allg. Chem. 2002,
628, 2697.
Received: October 29, 2012
Published Online: November 27, 2012
9] M. Jansen, Z. Anorg. Allg. Chem. 2012, 638, 1910.
Z. Anorg. Allg. Chem. 2013, 241–245
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
245