A metallic room-temperature oxide ion conductor

Article abstract of DOI:10.1002/anie.201402244

Nanoparticles of Bi₃Ir, obtained from a microwave-assisted polyol process, activate molecular oxygen from air at room temperature and reversibly intercalate it as oxide ions. The closely related structures of Bi₃Ir and Bi₃IrO_x (x≤2) were investigated by X-ray diffraction, electron microscopy, and quantum-chemical modeling. In the topochemically formed metallic suboxide, the intermetallic building units are fully preserved. Time- and temperature-dependent monitoring of the oxygen uptake in an oxygen-filled chamber shows that the activation energy for oxide diffusion (84meV) is one order of magnitude smaller than that in any known material. Bi₃IrO_x is the first metallic oxide ion conductor and also the first that operates at room temperature.

Full text of DOI:10.1002/anie.201402244

Angewandte
Chemie
DOI: 10.1002/anie.201402244
Oxide Ion Conductor Hot Paper
A Metallic Room-Temperature Oxide Ion Conductor**
Martin Heise, Bertold Rasche, Anna Isaeva, Alexey I. Baranov, Michael Ruck,* Konrad Schꢀfer,
Rainer Pçttgen, Jens-Peter Eufinger, and Jꢁrgen Janek
Abstract: Nanoparticles of Bi Ir, obtained from a microwave-
3
assisted polyol process, activate molecular oxygen from air at
room temperature and reversibly intercalate it as oxide ions.
The closely related structures of Bi Ir and Bi IrO (x ꢀ 2) were
3
3
x
investigated by X-ray diffraction, electron microscopy, and
quantum-chemical modeling. In the topochemically formed
metallic suboxide, the intermetallic building units are fully
preserved. Time- and temperature-dependent monitoring of the
oxygen uptake in an oxygen-filled chamber shows that the
activation energy for oxide diffusion (84 meV) is one order of
magnitude smaller than that in any known material. Bi IrO is
3
x
the first metallic oxide ion conductor and also the first that
operates at room temperature.
I
ntercalation chemistry is typically associated with layered
systems such as graphite, transition-metal dichalcogenides,
[
1–4]
double hydroxides, and clays (phyllosilicates).
Electro-
Figure 1. The time-dependent oxidation of Bi Ir to Bi IrO at room
3
3
x
chemical lithium intercalation was and is still widely inves-
tigated for battery applications. From a phenomenological
view the same holds for oxygen with a focus on nonstoichio-
metric oxides in, for example, solid oxide fuel-cell electrodes
and sensors. Yet, nobody has ever observed a fully reversible
uptake of oxygen into an intermetallic compound.
temperature was monitored by X-ray powder diffraction. The process is
associated with an expansion of the lattice, which can be followed,
e.g., by the shifts of the reflections 002 and 101 to lower angles. The
time interval between consecutive measurements is 75 min. Further
diffractograms for as-synthesized Bi Ir as well as for Bi IrO after 15 h
3
3
x
and after one year exposure to air see Figures S1–S3 in the Supporting
Information.
Here we report on nanoparticles of Bi Ir, a hitherto
3
uncharacterized intermetallic compound, that instantly take
up oxygen from air at room temperature. This is, however, not
the simple transformation to common oxides, but a fast
topochemical redox intercalation of molecular oxygen from
air. The process can easily be monitored by powder X-ray
diffraction (PXRD; Figure 1): within few hours the diffrac-
tion pattern of the intermetallic compound changes to that of
a phase with the composition Bi IrO (x ꢀ 2). Thereby, the
unit cell increases in size while oxygen is intercalated in
between the [Bi Ir] rods that constitute the structures of both
3
the innocent host and the loaded phase (Figure 2). The redox
intercalation is fully reversible. Treatment of Bi IrO with
3
x
hydrazine at room temperature or with hydrogen gas at 1508C
removes the oxygen and restores the initial structure of the
intermetallic compound.
One reason why the reversible absorption of oxygen by
Bi Ir has not been observed earlier is that this intermetallic
3
3
x
intensities of the diffraction peaks remain mostly unchanged
while their positions move towards lower angles. In fact, the
[
*] M. Heise, B. Rasche, Dr. A. Isaeva, Dr. A. I. Baranov,
Prof. Dr. M. Ruck
Fachrichtung Chemie und Lebensmittelchemie
Technische Universitꢀt Dresden
[**] We gratefully acknowledge Dr. I. Kunert (TU Dresden) for DSC
measurements. We are indebted to ZIH TU Dresden for computa-
tional facilities. We gratefully acknowledge Prof. U. Kaiser, Prof. C. T.
Koch, and Dr. D. Geiger (University of Ulm) for assistance in
conducting the TEM investigations, and E. Schmid (University of
Ulm) for ultramicrotomy of our samples. We thank Dr. U. Burkhardt
01062 Dresden (Germany)
E-mail: michael.ruck@tu-dresden.de
(MPI CPfS) for the measurement of EDX and WDX spectra, Dr. G.
Prof. Dr. M. Ruck
Auffermann (MPI CPfS) for ICP-OES measurements, and Dr. T.
Leichtweiss (University of Gießen) for XPS spectra. We are indebted
to Dipl.-Ing. U. C. Rodewald (University of Mꢁnster) for collecting
the single-crystal X-ray data. This work was supported by the
Deutsche Forschungsgemeinschaft.
Max Planck Institut fꢁr Chemische Physik fester Stoffe
Nçthnitzer Strasse 40, 01187 Dresden (Germany)
K. Schꢀfer, Prof. Dr. R. Pçttgen
Institut fꢁr Anorganische und Analytische Chemie
Universitꢀt Mꢁnster
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201402244.
Corrensstrasse 30, 48149 Mꢁnster (Germany)
J.-P. Eufinger, Prof. Dr. J. Janek
Institut fꢁr Physikalische Chemie
Justus-Liebig-Universitꢀt Gießen
Heinrich-Buff-Ring 58, 35392 Gießen (Germany)
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
the iridium atoms arrange in zigzag chains with short Ir–Ir
distances of 2.80 ꢀ. A substantially reduced electron density
on the iridium position was best explained by mixed
occupancy (EDX/WDX analyses, see Table S1 and Figure S4
in the Supporting Information) according to the formula
Bi (Ir0.77Cu0.17Ni0.06) for this crystal. No structural deformation
3
or superstructure could be detected, neither by X-ray or
electron diffraction (ED) nor by transmission electron
microscopy (TEM). High-resolution TEM imaging exhibits
equidistant zigzag chains of transition-metal atoms (Figure S5
in the Supporting Information). Angle-dependent structure
refinements also ruled out possible artifacts created by the
tremendous absorption of X-rays (the linear absorption
Figure 2. Single-crystal morphology and structure of Bi Ir. a) Hollow
3
intergrowth structure of Bi Ir crystals obtained from a bismuth flux.
3
b) Crystal structure of Bi Ir consisting of a pseudo-hexagonal packing
3
1
1
of [IrBi6/3Bi1/1] rods. c) Side view of a rod showing iridium atoms that
are coordinated by seven bismuth atoms in the shape of a capped
trigonal prism. The prisms share their rectangular faces and thereby
form zigzag chains of iridium atoms.
ꢁ
1
[13]
coefficient m(MoKa) of Bi Ir is 153 mm ; the lead of the
3
ꢁ
1
primary beam stop has “only” 139 mm ). Apparently the
copper and nickel traces in the elemental bismuth that has
been used for synthesis accumulate in the flux-grown crystals.
Crystals containing a lower amount of 3d metals have also
been identified.
compound is far from trivial to obtain. The standard metal-
lurgical approach—basically crystallization from a homoge-
nous high-temperature melt—is strongly hampered by the
drastic differences in the fundamental physical properties of
the two elements: bismuth evaporates 800 K below the
The absorption of oxygen is observed only for Bi Ir
3
nanoparticles. The Bi Ir crystals obtained by the intermetallic
3
[5]
melting point of iridium (24108C)! Furthermore, the
solubility of iridium in liquid bismuth is only 3% at 11008C.
Early investigations of the Bi–Ir system by melt reactions and
precursor method do not show the effect. In fact, the
nanoparticles grown by the microwave-assisted polyol process
are much smaller (maximum of the size distribution at 60 nm)
and have an amorphous shell (Figure 3a) that contains
besides organic molecules also bismuth and iridium cations,
as can be deduced from TEM contrast and X-ray photo-
electron spectroscopy. This shell seems to be essential for the
activation of molecular oxygen, since the reactivity is
dramatically reduced when the shell is removed. The latter
is possible by plasma cleaning of the TEM samples and also
subsequent annealing resulted in the binary phases Bi Ir and
2
[
6,7]
Bi Ir.
The structure types CoSb and Bi Ni were assigned
2 3
3
on the basis of Debye–Scherrer photographs. However, later
studies on transition-metal arsenopyrites could not reproduce
Bi Ir or any other binary Bi–Ir phase, neither in annealing
2
[
8]
experiments nor by chemical transport reactions.
One option for the synthesis of binary bismuth–iridium
compounds could be the application of high pressure to
suppress the evaporation of bismuth, in analogy to the
synthesis of Bi Co, which is not accessible under ambient
3
[
9]
pressure. So far, this approach has not yielded Bi Ir.
3
Alternatively, iridium can be provided in more reactive
forms: We obtained Bi Ir single crystals in low yield from the
3
intermetallic precursor Sm Ir Sb , which was dissolved in
3
3
7
molten bismuth at 11008C, while phase-pure samples of Bi Ir
3
nanoparticles became available when we reduced the metal
salts in a microwave-assisted polyol process at 2308C,
a method that had already been applied to synthesize
[10]
[11]
[12]
phase-pure Bi Ni,
Bi Ir,
2
and BiRh nanoparticles.
3
While the shape of the nanoparticles is unremarkable, the
larger crystals obtained from the flux showed the unusual
intergrowth morphology of hollow square tubes (Figure 2a).
X-ray diffraction on single crystals obtained by the
intermetallic precursor method confirmed the predicted
orthorhombic (Pnma) Bi Ni-type structure (Figure 2b) with
3
lattice parameters a = 8.970(2) ꢀ, b = 4.190(6) ꢀ, and c =
3
1
1.511(5) ꢀ (V= 432.6(1) ꢀ ) at 208C. For the nanoparticles
of Bi Ir slightly different lattice parameters of a = 8.900(2) ꢀ,
3
3
b = 4.170(1) ꢀ, and c = 11.602(3) ꢀ (V= 430.6(2) ꢀ ) were
Figure 3. Electron microscopy and diffraction of Bi IrO . a) Bi IrO
3 x 3 x
(
xꢂ1) particle at high resolution revealing an amorphous shell
determined (Figure S1 in the Supporting Information). The
iridium atoms are coordinated by seven bismuth atoms in the
shape of a capped trigonal prism. The Bi–Ir distances range
from 2.76 to 2.92 ꢀ, comparable to the sum of the covalent
surrounding the crystalline core. b) A selected electron diffraction
pattern of a particle after plasma cleaning. The presence of forbidden
reflections is due to double-diffraction phenomena. c,d) Bright-field
imaging and an indexed ring diffraction pattern of Bi IrO powder.
From both the spot and ring ED patterns, the lattice parameters of
a=9.44 ꢂ, b=3.8 ꢂ, c=12.7 ꢂ for xꢂ1 can be deduced.
3
x
[
5]
radii of 2.78 ꢀ. By sharing their rectangular faces the
1
1
trigonal prisms form [IrBi Bi ] rods (Figure 2c). Thereby,
6/3
1/1
2
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
improves the quality of the ED patterns of the Bi IrO crystals
are fast oxide ion conductors at temperatures above
3
x
[
17,18]
(
Figure 3b and Figure S6 in the Supporting Information).
6508C,
(g-Bi O ), or 1.69 (d-Bi O ). Bond-valence sums of 2.07 and
these valence sums are only 0.69, 1.18, and 1.30
Nonetheless, the oxygen uptake is a volume effect as has been
shown by PXRD, ED, and quantitative monitoring of the
oxygen pressure in a closed cell during oxygen uptake (see
2
3
2
3
1.64 indicate that the integration of at least one of the oxide
ions in Bi IrO is also comparatively weak. Moreover, the
3
2
below). The reciprocal space sectioning of Bi IrOx nano-
particles confirms that their crystal structure is very similar to
diffusion paths between the intermetallic rods are straight and
there is an excess of closely spaced voids with low hopping
barriers between them. The combination of these advanta-
geous factors nicely explains the observed ultrahigh mobility
of oxide ions even at room temperature.
3
that of intermetallic Bi Ir except for minor changes in unit cell
3
parameters (a = 9.44 ꢀ, b = 3.8 ꢀ, c = 12.7 ꢀ for x ꢂ 1 from
ED).
Alternatively, Bi IrO can be synthesized within minutes
For an intermetallic compound, Bi Ir is unusually elec-
3
x
3
by treating Bi Ir nanoparticles with aqueous H O solution
tron-rich. The highest occupied states close to the Fermi level
are involved in bonding between bismuth atoms of neighbor-
ing rods, as can be deduced from the band dispersion in the
directions orthogonal to the rods (Figure 5a: G-X and G-Z).
The partial ELI-D for the states close to the Fermi level shows
that they originate mainly from the lone pairs of bismuth
atoms and have minor impact on the bonding between metal
atoms within a single rod (Figure 5e). Upon oxidation, these
states are depopulated and the inter-rod bonding is replaced
by electrostatic interactions between positively charged
bismuth atoms and oxide ions. Still, the material remains
metallic (Figure 5b). A combined k-space and real-space
3
2
2
(
30%). We also observed that Bi Ir nanoparticles remove
3
physically dissolved molecular oxygen from ethanol at room
temperature.
Because the combination of small nanoparticles and
extreme X-ray absorption effects are not conducive to
conventional Rietveld refinement, structure models for
Bi IrO were developed by quantum chemical means and
3
x
the calculated diffraction diagrams were compared to the
observed patterns. Based on the expansion of the inter-rod
distances in the Bi Ir structure three possible positions for
3
oxide ions were identified. With two of these positions
occupied, three possible models can be constructed. DFT-
based geometry optimization yielded stable structures in all
cases. The one with lowest total energy is displayed in
Figure 4. Its calculated diffraction pattern nicely matches the
measured powder diffractogram of the oxidized sample
(
Figure S2 in the Supporting Information).
Figure 4. Crystal structure of Bi IrO projected along the intermetallic
3
2
rods (b axis). The increase in the distances between the rods generates
space for oxide ion diffusion and storage. Besides tetrahedral and
octahedral sites that are occupied by oxide ions (red), additional
tetrahedral voids (gray) are available for mass transport and further
oxygen uptake.
Figure 5. Electronic band structure and real-space bonding indicators
In Bi IrO , one type of oxide ions has four bismuth
3
2
for Bi Ir and Bi IrO . a,b) Band structure plots along the paths shown
3
3
2
neighbors, the other type six. BiꢁO bond lengths range for the
3 3 2
in Figure S8 in the Supporting Information for Bi Ir and the Bi IrO ,
tetrahedral coordination from 2.23 to 2.45 ꢀ (average
respectively. c,d) Localization domains of the ELI-D indicator, which
mark bonding between two Ir atoms (green) and between Ir and Bi
atoms (capping Bi3: orange; Bi1 and Bi2: yellow). The isosurface
values for the yellow and orange domains are near 1.0 and for the
green domains 0.96 in Bi IrO (d) and 0.97 in Bi Ir (c). e) Partial ELI-D
2
2
.34 ꢀ), for the octahedral case from 2.26 to 2.99 ꢀ (average
[14]
.66 ꢀ). The bond-valence concept provides a rough esti-
mate of the strength of the oxygen fixation compared to that
[
15]
3
2
3
of known bismuth oxides. In a-Bi O ,
the bond-valence
2
3
(
pELI-D) diagram for the states in the interval ꢁ1.6 eV to 0 eV, which
sums of the three crystallographically independent oxide ions,
corresponds to approximately 4 electrons per formula unit. f) The total
number of electrons in selected ELI-D basins, showing that oxidation
affects primarily the Bi atoms.
that is, the sum of all OꢁBi bonding interactions, are 1.93,
[16]
[16]
1
.98, and 2.05. In the case of g-Bi O
and d-Bi O , which
2 3
2
3
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
bonding analysis (Figure 5c,d) revealed that the sum of BiꢁIr
bonds, which are governing the bonding inside the rods, is
indifferent to an oxygen content up to at least x = 2. While the
IrꢁIr bonding is somewhat weakened, the number of elec-
trons on the iridium atom and thereby its oxidation state
remain unchanged. As the bismuth atoms remain strongly
bonded to iridium, they are not available for the formation of
Bi O , which would be expected as the trivial product of the
2
3
oxidation. Nonetheless, the bismuth atoms are oxidized. With
respect to the crystallographically independent atoms, the
charge distribution in Bi Ir can be approximated as
3
+
0.5
+0.5
ꢃ0 ꢁ1
Bi1 Bi2 Bi3 Ir , while in Bi IrO2 it is close
Bi1 Bi2 Bi3 Ir (O ) . The capping bismuth atom,
3
+1.5
+1.5
+2 ꢁ1
ꢁ2
2
Bi3, is most affected by oxidation; however, its bonding to
the iridium atom is not weakened, according to the total
number of electrons found in bonding basins (Figure 5 f). A
similar situation has been found in the stable subhalides of
Figure 6. Oxygen uptake, reversibility, and kinetics of oxygen diffusion.
a) Oxygen uptake at different temperatures in an oxygen-filled cham-
ber. b) Profile of the absorption of dry oxygen in a pressure cell at
[19,20]
Bi Ni.
3
The X-ray diffraction experiment shows the instantaneous
formation of the second phase with a larger unit cell in the
early stages of the oxygen uptake. Based on LeBail refine-
ment, the lattice parameters change by Da =+ 5.0%, Db =
258C and the derived oxygen diffusion coefficient. c) Temperature
dependence of the chemical diffusion coefficient and activation energy
for oxide transport in Bi IrO . d) Coulometric titration of a sample that
3
x
was stored in air at room temperature for four days. The reduction
process in argon/hydrogen atmosphere at 1508C already started
during the heating process at 308C and was finished after six hours.
The total oxygen content per formula unit of the starting material is
calculated to be x=0.31.
ꢁ
5.8%, Dc =+ 9.5% and the volume by DV=+ 8.3%. The
elongation of a and c axes refers to an increase in the distance
between the prism rods and opens the space for oxygen
intercalation. The absolute volume change is approximately
3
3
9 ꢀ . The radius of 1.42 ꢀ for a highly coordinated oxide ion
[
21,22]
tabulated by Shannon and Prewitt
isotropic volume of 11.5 ꢀ . Taking typical packing densities
corresponds to an
3
The profiles of the absorption of dry oxygen in the
pressure cell at 25, 45, and 608C were fit with a model for
reactions controlled by one-dimensional diffusion of a gaseous
species into a spherical solid including the exchange coef-
ficient of the surface (Figure 6b). The fits show that the
intercalation is predominantly controlled by diffusion. The
(
ꢀ 72%) into account, the expected maximum of the oxygen
uptake (x) should be about two oxide ions per formula unit.
This prediction is corroborated by the effective volume of
3
[23]
1
8 ꢀ for an oxide ion, which was given by Biltz.
The
difference between the chemical analyses of freshly synthe-
ꢁ
22
2
ꢁ1
sized Bi Ir nanoparticles and an oxidized sample (air, 20 d,
diffusion coefficient of 1.2 ꢁ 10 m s appears unimpressive
3
ꢁ
19
2
ꢁ1
[24]
2
08C) likewise suggests an oxygen uptake of x = (2.0 ꢃ 0.2)
compared to that of YSZ (10 m s at 1508C), yet the
value was determined at 258C! Hence the diffusion of oxygen
ions inside the solid is unprecedentedly fast in this temper-
ature regime. The linear fit of the temperature dependence of
the diffusion coefficients reveals an unmatched low activation
energy of only 84 meV (Figure 6c). Typical values for the
anion transport in oxides range from 0.8 to 1.0 eV.
atoms per formula unit. Yet, the analyses are assumed to be
biased by the organic shell.
In contrast to the single-stage expansion of the structure,
monitoring of the pressure in an oxygen-filled chamber shows
that after a rapid initial uptake of oxygen by the intermetallic
nanoparticles, the process continues at a moderate, almost
constant rate (Figure 6a). This suggests an initial structural
expansion step that is followed by subsequent diffusion-
controlled filling of the generated channel system. The
negligible incubation time is in accordance with a topotactical
reaction mechanism and suggests very low activation ener-
gies, including the activation of the double bonds in the
oxygen molecules. If one applies the ideal gas law, composi-
tions of Bi IrO after 30 h and Bi IrO after 96 h at 258C can
Bi IrO (x ꢀ 2) can be fully reduced to the intermetallic
3
x
compound Bi Ir by treatment with hydrogen. A coulometric
3
[
25]
titration of oxygen in an OXYLYT device
in argon/
hydrogen atmosphere (Figure 6d) demonstrates that the
reduction process starts already at about 308C. After 6 h at
1508C the reduction is complete. Alternatively, solution-
based reduction can be performed at room temperature by
using hydrazine (80 vol% in aqueous solution) or Super-
hydride (lithium triethylborohydride; 1m in THF). Upon
repeated oxidation and complete reduction the material
becomes progressively amorphous and the activity for oxygen
uptake decreases drastically. It has to be tested how the
degree of oxygen loading and unloading influences the cycling
capability.
3
1.0
3
1.8
be deduced. An increase in temperature by 58C results in
Bi IrO after only four days. Within the same period the
3
2
composition Bi IrO can be attained if the reaction temper-
3
3
ature is 458C. Exposure to pure oxygen atmosphere at 608C
ultimately results in irreversible oxidation to Bi O3 and
2
precipitation of elemental iridium. The presence of humidity
during the oxidation seems to lower the activation energy of
the oxidation process, which is reflected in a faster initial
uptake of oxygen (Figure S7 in the Supporting Information).
In conclusion, Bi Ir proved to be an astonishing material,
3
especially in nanocrystalline form. Its ability to activate
molecular oxygen at room temperature, either from the gas
4
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
phase or physically dissolved in solvents, by reversible redox
intercalation could be exploited for sensors, electrodes of
solid oxide fuel cells, and oxidation catalysts. Bi IrO is the
first metallic oxide ion conductor and also the first that
operates at room temperature, showing unusually low acti-
vation energy for oxygen ion transport.
[9] U. Schwarz, S. Tencꢃ, O. Janson, C. Koz, C. Krellner, U.
Burkhardt, H. Rosner, F. Steglich, Y. Grin, Angew. Chem. 2013,
25, 10038 – 10042; Angew. Chem. Int. Ed. 2013, 52, 9853 – 9857.
10] T. Herrmannsdçrfer, R. Skrotzki, J. Wosnitza, D. Kçhler, R.
Boldt, M. Ruck, Phys. Rev. B 2011, 83, 140501.
11] R. Boldt, A. Grigas, M. Heise, T. Herrmannsdçrfer, A. Isaeva, S.
Kaskel, D. Kçhler, M. Ruck, R. Skrotzki, J. Wosnitza, Z. Anorg.
Allg. Chem. 2012, 638, 2035 – 2043.
1
3
x
[
[
Received: February 10, 2014
[12] D. Kçhler, M. Heise, A. I. Baranov, Y. Luo, D. Geiger, M. Ruck,
Published online: && &&, &&&&
M. Armbrꢂster, Chem. Mater. 2012, 24, 1639 – 1644.
[
[
[
13] A. R. Stokes, A. J. C. Wilson, Proc. Phys. Soc. London 1941, 53,
58 – 662.
14] N. E. Brese, M. OꢄKeeffe, Acta Crystallogr. Sect. B 1991, 47,
92 – 197.
15] S. A. Ivanov, R. Tellgren, H. Rundlçf, V. G. Orlov, Powder Diffr.
001, 16, 227 – 230.
6
Keywords: intermetallic phases · ion conductors ·
metastable compounds · subvalent compounds · topochemistry
.
1
2
[
1] M. S. Whittingham, A. J. Jacobson, Intercalation Chemistry,
Academic Press, New York, 1982.
[16] H. A. Harwig, Z. Anorg. Allg. Chem. 1978, 444, 151 – 166.
[17] T. Takahashi, H. Iwahara, Mater. Res. Bull. 1978, 13, 1447 – 1453.
[18] H. A. Harwig, A. G. Gerards, J. Solid State Chem. 1978, 26, 265 –
[
2] T. Enoki, M. Suzuki, M. Endo, Graphite Intercalation Com-
pounds and Applications, Oxford University Press, New York,
274.
2003.
[19] M. Ruck, Z. Anorg. Allg. Chem. 1997, 623, 243 – 249.
[20] M. Ruck, Z. Anorg. Allg. Chem. 1999, 625, 453 – 462.
[21] R. D. Shannon, C. T. Prewitt, Acta Crystallogr. Sect. B 1969, 25,
[
[
[
[
[
[
3] W. Mꢂller-Warmuth, R. Schçllhorn, Progress in Intercalation
Research, 2nd ed., Springer, Berlin, 2012.
4] S. M. Auerbach, K. A. Corrado, P. K. Dutta, Handbook of
Layered Materials, CRC, New York, 2004.
925 – 946.
[
[
22] R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751 – 767.
23] W. Biltz, Raumchemie der festen Stoffe, Leopold Voss, Leipzig,
5] J. Emsley, The Elements, Oxford University Press, New York,
1
998.
6] N. N. Zhuravlev, E. M. Smirnova, Sov. Phys. Crystallogr. 1966,
0, 694 – 697.
1934.
[
24] R. Rçwer, G. Knçner, K. Reimann, H. E. Schaefer, U. Sçdervall,
Phys. Status Solidi B 2003, 239, R1 – R3.
25] K. Teske, H. Ullmann, N. Trofimenko, J. Therm. Anal. 1997, 49,
1
7] T. B. Massalski, H. Okamoto, P. R. Subramanian, in Binary Alloy
Phase Diagrams, 2nd ed. (version 1.0), ASM International, 1996.
8] A. Kjekshus, Acta Chem. Scand. 1971, 25, 411 – 422.
[
1211 – 1220.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Oxide Ion Conductor
Oxygen topochemistry: Nanoparticles of
Bi Ir, a hitherto uncharacterized interme-
3
M. Heise, B. Rasche, A. Isaeva,
A. I. Baranov, M. Ruck,* K. Schꢁfer,
R. Pçttgen, J.-P. Eufinger,
tallic compound, reversibly intercalate
oxygen from air at room temperature. In
the resulting metallic suboxide, the
J. Janek
&&&& — &&&&
intermetallic building units are preserved.
The activation energy for oxide diffusion
is one order of magnitude smaller than
that in any known material. Bi IrO is the
A Metallic Room-Temperature Oxide Ion
Conductor
3
x
first metallic oxide ion conductor and also
the first that operates at room temper-
ature.
6
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!