JOURNAL OF SOLID STATE CHEMISTRY 140, 14—19 (1998)
ARTICLE NO. SC987798

Synthesis and Magnetic Properties of New Series of One-Dimensional
Oxides Ca3Co11xB12xO6 (B 5 Ir, Ru)
Hiroshi Kageyama,1 Kazuyoshi Yoshimura, and Koji Kosuge
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
Received June 30, 1997; in revised form February 19, 1998; accepted February 24, 1998

that each AO —BO chain is surrounded by six chains, thus
3
3
forming a triangular net as seen in Fig. 1b. Therefore we also
expect cooperative phenomena caused by the triangulararrangement of the chains.
Recently, the crystal structure of Ca Co O was deter3 2 6
mined by Fjellva> g et al. (9); Ca Co O is isostructural with
3 2 6
Sr ZnIrO (8), and the Co ions occupy both the A and the36
B sites. The ferromagnetic Ising-spin chains order ferrimagnetically on the triangular lattice below 25 K as a resultof the antiferromagnetic interaction between the chains(11—13). Furthermore, by our Mössbauer measurements of
Ca (Co57Fe) O , the quantum levels of Fe3` ions3
0.99
0.01 2 6
were first observed in magnetically dense systems (14). This
remarkable observation is attributed to the large difference
between magnetic characters of the host (Ising) and impurity (Heisenberg) spins.
Encouraged by the peculiar magnetic properties on
Ca Co O , we tried to synthesize Co-contained compounds
3 2 6of this structure series. As a result, new compounds with thechemical formula Ca CoIrO and Ca CoRuO were suc3
63
6
cessfully prepared. As expected, the solid solution seriesof Ca Co Ir O and Ca Co Ru O (04x41)
3 1`x 1~x 6
3 1`x 1~x 6
were also prepared. Here we report the synthesis, structures,and magnetic properties of these systems.

New one-dimensional compounds Ca3CoBO6 (B 5 Ir, Ru)with K4CdCl6-type structure have been synthesized by conventional solid state reactions. Both compounds adopt the rhombohedral symmetry with the space group R31 c; a 5 9.1811(1) As ,c 5 10.8232(3) As , Z 5 6 (hexagonal expression) for Ca3CoIrO6
and a 5 9.1921(3) As , c 5 10.7784(7) As , Z 5 6 for Ca3CoRuO6 .
One-dimensional chains are built by alternating face-shared
CoO6 octahedra and BO6 trigonal prisms. The magnetic susceptibility of Ca3CoIrO6 shows an abrupt drop at 30 K, as seen in thecase of Sr3NilrO6 , suggesting that ferromagnetic chains couple
antiferromagnetically. On the contrary, Ca3CoRuO6 is an ordinary antiferromagnet with TN 5 55 K. We have also succeededin preparing the solid solution series, Ca3Co11x Ir12xO6 andCa3Co11xRu12xO6 (04x41), and magnetic properties of thesesystems were investigated. ( 1998 Academic Press

1. INTRODUCTION

Since the discovery of Sr CuPtO (1), the structure of
36which is related to the one of K CdCl (2), many com4
6
pounds with the general formula A@ ABO (A@"Sr, Ca, 2 ;3
6
A"Ni, Cu, Zn, 2; B"Ir, Pt, Ru, 2 ) have been synthesized and investigated from the viewpoints of their structures and magnetic properties (3—12). Figure 1a shows theperspective view of A@ ABO -type structure along the hexa3
6gonal [110] direction, which consists of infinite chains ofalternating face-sharing AO trigonal prisms (A site) and6
BO octahedra (anti-trigonal prisms, B site). A one-dimen6
sional (1-D) magnetic character is expected because the
AO —BO chains are separated by the A@ ions. The members
3
3of the A@ ABO family are known to show various magnetic
3
6
behaviors, some of which are discussed in terms of the 1-D
magnetic models, such as a random quantum spin chain
paramagnet model for Sr CuPt Ir O (6), a 1-D Heisen3
0.5 0.5 6
berg model for Sr CuPtO (4), and a 1-D Ising model for
3
6
Sr ZnIrO (8). Another structural feature of this family is
36

2. EXPERIMENTAL

Polycrystalline compounds of Ca Co Ir O and3 1`x 1~x 6
Ca Co Ru O (04x41) were prepared by conven3 1`x 1~x 6
tional solid state reactions. The stoichiometric amounts ofreagents CaCO (99.99%), CoO (99.99%), Ir (99.9%), and3
Ru (99.99%) were sufficiently mixed using an agate mortar,pressed into pellets and calcined in air at 1173 K for
one day. Then, the samples were heated in air for 1 or 2
weeks at temperatures in the range 1273—1423 K for Ca3
Co Ir O and 1273—1500 K for Ca Co
Ru O
1`x 1~x 6
3 1`x 1~x 6
with intermediate grindings. Because Ca Co O decom3 2 6poses to CaO and CoO at 1299 K (15), lower temperatures are required for the preparation of the samples withsmall x.

1 Present address: Institute for Solid State Physics, University of Tokyo,
Roppongi, Minato-ku, Tokyo 106-8666, Japan. E-mail: kage@issp.utokyo.ac.jp.
140022-4596/98 $25.00
Copyright ( 1998 by Academic Press
All rights of reproduction in any form reserved.

NEW ONE-DIMENSIONAL OXIDES

15

FIG. 1. Schematic illustration of the structure of A@ ABO . (a) The perspective view along the [110] direction. The open and shaded polyhedra
3
6
represent BO octahedra (anti-trigonal prisms) and AO trigonal prisms, respectively. The open circles show A@ atoms. (b) The projection along the c axis.
6
6
The black circles represent A@ and B atoms, the large open circles represents the oxygen, and the small open circles represent A atoms.

Powder samples were structurally characterized using
a high power (18 kW) X-ray diffractometer (Mac Science,
M18XHF22) with CuKa radiation, j"1.5405 As . Data wererecorded in steps of 0.02° in 2h between 5° and 80° (Bragg
Brentano geometry) and the counting time was 0.1 sec. The
unit-cell parameters were determined by the least-square
fitting to some characteristic indexes in the powder X-ray
diffraction patterns. The Rietveld analysis (16) of the powder
X-ray diffraction data of the end compounds Ca CoIrO
3
6
and Ca CoRuO was performed using the refinement pack3
6
age Rietan (17). The structure of Sr NiIrO was used as3
6
a starting model. Data for the Rietveld refinements werecollected over 5°42h480° in 0.02° steps, with integration
times of 1.0 sec.
From the thermogravimetric analysis measured between
300 and 1273 K in flowing O , the weight change was found2
to be within 0.1 wt% for all the samples. Considering that
fact, it can be assumed that the oxygen content is almost
stoichiometric (i.e., 5.97—6.00).
Magnetic properties were measured on powder samples
using a Quantum Design MPMS SQUID magnetometer.
Measurements were carried out in various magnetic fields inthe temperature range of 4 K4¹4300 K after cooling thesample in zero magnetic field (zero-field cooled, ZFC) andalso after cooling in the measuring field (field cooled, FC).
Magnetic susceptibility in the high-temperature range
300 K4¹4770 K was measured at H"0.5 T using atorsion magnetic balance.

(see the peak around at 37.5°), its XRD intensity is verysmall so that it would not disturb any intrinsic magnetic
properties of Ca CoIrO . The powder X-ray Rietveld re3
6finement was carried out for Ca CoIrO both in the space3
6
group of Sr ZnIrO (8), R3M c, and in that of the structurally
3
6
related Sr CuPtO (3), C2/c. All attempts to refine in the36
monoclinic space group diverged. On the other hand, refinement of the rhombohedral space group R31 c gave a unit cellof a"9.1811(1) As and c"10.8232(3) As and quickly converged to R "14.5% and R "12.3%. Here we assumed
81
1that the Co and the Ir ions occupy the A and the B sites,
respectively, that is, the chain consists of alternating facesharing CoO trigonal prisms and IrO octahedra. Ob6
6served and calculated interplanar spacings and intensities of
Ca CoIrO are given in Table 1. It is likely that the poor
3
6
convergency is the result of the preferred orientation of thesample as is often seen in the case of one-dimensional

3. RESULT AND DISCUSSION

Crystal Structure
The powder XRD pattern of Ca CoIrO is shown in
3
6
Fig. 2. Although an unknown impurity phase was observed

FIG. 2. X-ray Rietveld analysis for Ca CIrO showing the observed,
3
6
calculated, and difference patterns.

16

KAGEYAMA, YOSHIMURA, AND KOSUGETABLE 1
Observed and Calculated Powder XRD of Ca3CoIrO6(R31 c, a 5 9.1811 As , c 5 10.8232 As )
hkl

d
0"4

d
#!#-

I/I (obs)
0

I/I (calc)
0

110
012
202
113
300
122
104
220
024
131
312
214
223
042
321
125
410
232
134
116
404
413
143

4.59044.47553.20872.84122.65272.63002.56442.29852.2403
2.16412.04482.01451.9395
1.86961.8031
1.76154.59064.47373.20392.83662.65042.62732.56152.2953
2.23692.16082.04222.01081.93661.86591.79871.7564
1.73511.72851.7094
1.67891.60201.56361.5636

100
50
15
14
99
13
14
11
25
8
27
46
20
4
2
1

100
50
26
13
88
21
15
8
28
5
20
43
13
5
1
1
14
2
18
11
7
1
1

1.7379N
1.71251.68281.60501.5667N

23N
17
7
6
3N

compounds (4). In addition, a small amount of Ir may belost as IrO because of high volatility. Although several
3
attempts were made to refine the fitting by varying site
occupancies e.g., the deficiencies and/or the substitution in
the Ir site, these did not improve the result.
The representative powder XRD patterns for Ca Co
3 1`x
Ir O are shown in Fig. 3. It is clear that the synthesis of
1~x 6
Ca Co
Ir O solid solution series is successful for the
3 1`x 1~x 6
whole range of x (04x41). The top of Fig. 4 represents the
crystallographic unit-cell parameters with the hexagonal
expression as a function of composition x. The lattice parameters [a"9.0710(1) As , c"10.3751(2) As ] for Ca Co O
3 2 6
are almost in good agreement with those previously reported (9). Both a and c shrink with increasing x. The Ir andthe Co ions are considered to be distributed randomly on
the B site because the XRD pattern has no additional peakwhich indicates the existence of ordering between the Ir andthe Co ions at the B site.
Next, the representative powder XRD patterns for
Ca Co Ru O are shown in Fig. 5, which tells us the
3 1`x 1~x 6
successful synthesis of the Ru-based solid solution. No impurity was detected for x50.1 from the XRD patterns,
whereas, as for x"0 (Ca CoRuO ), a small amount of
3
6
CaRuO was detected as marked by asterisks in Fig. 5. The
3
powder X-ray Rietveld refinement for Ca CoRuO was
3
6
performed in the space groups of R31 c and C2/c, where the

FIG. 3.

Observed powder XRD pattens for Ca Co Ir O .
3 1`x 1~x 6

Co and the Ru ions are assumed to occupy the A and theB sites, respectively. The result is the same as that for
Ca CoIrO ; only the refinement in the former space group3
6
of R31 c converged to R "15.5% and R "17.5%, giving
811FIG. 4. Crystallographic unit-cell parameters as a function of composition x in the Ca Co Ir O (top) and Ca Co Ru O (bottom)
3 1`x 1~x 6
3 1`x 1~x 6
solid solution series. The errors on cell constants for the samples with
0(x(1 are within 0.001 As .

17

NEW ONE-DIMENSIONAL OXIDESTABLE 2
Observed and Calculated Powder XRD of Ca3CoRuO6(R31 c, a 5 9.1921 As , c 5 10.7784 As )FIG. 5. Observed XRD patterns for Ca Co Ru O . The peaks
3 1`x 1~x 6
marked by asterisk correspond to CaRuO .
3

lattice parameters of a"9.1921(3) As and c"10.7784(7) As .
Observed and calculated interplanar spacings and intensities of Ca CoRuO are given in Table 2. The reason for3
6
the poor convergency is also attributable to the sample
orientation and the volatility of RuO at high temperatures.
4
The composition dependence of the unit-cell parameters for
the Ca CoRuO solid solution series is shown at the bottom
3
6
of Fig. 4. As in Ca Co Ir O , both a and c decrease
3 1`x 1~x 6
with increasing x.

Magnetic Properties
In contrast to the similar composition dependence of theunit-cell parameters between the Ir- and Ru-based solid
solutions, magnetically, the two systems differ significantly.
The temperature dependence of magnetic susceptibility
M/H for Ca CoIrO measured at 0.5, 1.0, and 5.0 T is3
6shown in Fig. 6. The M/H vs. ¹ curves obey the
Curie—Weiss law above 200 K. The positive value of the
Weiss temperature (¹ "165 K) implies the ferromagneticW
intrachain interaction. The observed paramagnetic Bohrmagneton number P "3.73 k /f.u. is close to the theoret%&&B
ical value of 4.24 k for S"3/2 (Co2`, high spin) andB
S"1/2 (Ir4`). However, it should be noted that the analysis
using the data of powder samples involves ambiguity because electron spin characters in low-dimensional magnets

hkl

d
0"4

d
#!#-

I/I (obs)
0

I/I (calc)
0

110
012
*
202
113
*
300
122
104
220
024
131
312
214
223
042
321
006
125
410
134
116
404
413
143

4.59974.45353.8241
3.19742.82552.71682.65432.62712.54472.29902.22662.16322.04302.0044
1.93491.86681.80111.79064.59604.4513—
3.19752.8240—2.65352.62482.54382.29802.2257
2.16262.04202.0032
1.93381.86611.8004
1.78971.74801.73711.7052
1.66781.59881.56281.5628

56
29
4
5
40
7
100
2
9
4
37
18
20
60
46
4
2
3

72
30
—
4
28
—
100
2
11
4
33
11
14
55
34
1
2
2
2
14
18
9
6
5
2

1.7379N
1.70601.66871.5994
1.5667N

17N
21
7
6
3N

The asterisks correspond to the peaks of CaRuO .
3

are often highly anisotropic, and thus an observed magnetization gives an averaged one over the three crystallographic axes. Add to this that there may be an orbital
contribution to the effective spin moment. Therefore, themeasurements using a single crystal or an aligned sample
are necessary in order to make quantitative analysis.
Below 150 K, there is a positive deviation from theCurie—Weiss law. The value of M/H depends on H for¹480 K. For the ZFC sample, there is a precipitous dropin the magnetization at ¹ "32 K to that of a constant low#
value for ¹(25 K. Below ¹ , the irreversibility in M/H vs.
#¹ curves appears between ZFC and FC processes, indicating that a ground state is not a spin singlet state but (canted)
antiferromagnetic state. It can be deducible that ferromagnetic chains couple antiferromagnetically below ¹ , which#
can explain the sharp drop in the magnetization. According
to Ref. 5, Sr NiIrO shows a similar magnetic behavior to3
6
Ca CoIrO : the M/H vs. ¹ obeys the Curie—Weiss law at
3
6high temperatures, for 70 K(¹(150 K there is a positive
deviation from the Curie—Weiss law, and at temperatures
below ¹ "21 K there is a precipitous drop in the magnetiz#ation. Nguyen et al. suggested from the abrupt drop in themagnetization at ¹ that this material should achieve a#singlet ground state (5). However, they performed only ZFC

18

KAGEYAMA, YOSHIMURA, AND KOSUGE

FIG. 6. M/H vs. ¹ curves of Ca CoIrO measured in a field of 0.3, 1.0,
3
6
and 5.0 T. Solid marks represent ZFC, and open marks represent FC.

magnetization measurements. We performed the FC and
ZFC magnetization measurements on Sr NiIrO and found
3
6
that Sr NiIrO also exhibits FC and ZFC divergency at ¹ .
3
6#Consequently, both Ca CoIrO and Sr NiIrO are con3
6
3
6
sidered as canted antiferromagnets below ¹ , even though#
the neutron diffraction study for Sr NiIrO failed to ob3
6serve magnetic Bragg peaks at low temperatures (5). There
are many Ir-based compounds in this family such as
Sr CaIrO , Sr CuIrO , and Sr CdIrO (5, 7, 8), but only
3
6
3
6
3
6
Ca CoIrO and Sr NiIrO show such complex magnetic
3
6
3
6
behaviors. We do not presently give an explanation for thedifference in the magnetic behaviors of two compounds andthe others. Further study is needed in order to make clear
the magnetic structure of Ca CoIrO and Sr NiIrO .
3
6
3
6The temperature dependence of magnetic susceptibility
for Ca Co Ir O are shown in Figs. 7 and 8, for
3 1`x 1~x 6
x40.5 and x'0.5, respectively. The magnetic susceptibility in the high-temperature range can be fitted to theCurie—Weiss law for all x. In Fig. 9, the composition dependence of ¹ and P is presented. As x increases, the value ofW%&&¹ decreases for x(0.7 and then increases. P increases
W%&&monotonously with x. The abrupt drop in the M/H curves
appears for the ZFC samples with x40.5. Remarkable
future is that ¹ is almost independent of x; for Ca Co#
3 1.5
Ir O , ¹ is 28 K only 4 K lower than in the case of the end
0.5 6 #
compound Ca CoIrO . Although in the case of Ca CoIrO
3
6
3
6
the deviation from the Curie—Weiss law for 70 K(¹(200 K was obtained as mentioned previously, such anomaly
was not observed for x"0.2, 0.3, and 0.5. For x'0.5, anabrupt drop in the magnetization disappears. Instead, there
is a broad maximum in the M/H vs. ¹ curves around 10 K.
The decrease of ¹ with x would be accounted for theW

FIG. 7. Temperature dependence of magnetic susceptibilities M/H at
H"0.5 T for Ca Co Ir O (x40.5). Solid marks represent ZFC,
3 1`x 1~x 6
and open marks represent FC.

disappearance of ¹ . When the ferromagnetic intrachain#interaction becomes smaller, the interchain interaction
would also get weak. This would prevent the ferromagnetic
chains from coupling antiferromagnetically. As shown in theinset of Fig. 8, the abrupt increase in magnetization wasobserved for x50.97, which corresponds to the transition
from a paramagnetic state to a ferrimagnetic state (11—13).
In Fig. 10, we show the temperature dependence of themagnetic susceptibility of Ca Co Ru O
solid
3 1`x 1~x 6

FIG. 8. Temperature dependence of magnetic susceptibilities M/H at
H"0.5 T for Ca Co Ir O (x'0.5). Solid marks represent ZFC,
3 1`x 1~x 6
and open marks represent FC. Inset: Enlarged plot for x"0.9, 0.97, and 1.

19

NEW ONE-DIMENSIONAL OXIDES

Magnetic susceptibility for x"0, 0.1, 0.3, and 0.5 displays
an ordinary antiferromagnetic transition. The antiferromagnetic ordering temperature ¹ decreases with x; ¹ "55,NN
50, 36, and 34 K for x"0, 0.1, 0.3 and 0.5, respectively,
which is consistent with the composition variation of¹ (Fig. 9). For the samples with x'0.7, there is a broadWmaximum in the M/H vs. ¹ curves around 10 K. This broad
maximum is also observed in the case of Ca Co Ir O .
3 1`x 1~x 6
4. SUMMARY

FIG. 9. Weiss temperature ¹
and P
per formula unit ofW%&&
Ca Co B O (B"Ir, Ru) as a function of composition x. Solid curves
3 1`x 1~x 6
are guides to the eye.

solution series. Above 100 K, the M/H vs. ¹ curves were wellfitted to the Curie—Weiss law. The composition variations of¹ and P are shown in Fig. 8. Both ¹ and P increase
W
%&&
W
%&&
consistently with x. P "2.42 k /f.u for Ca CoRuO sup%&&B
3
6
ports the spin configuration of S"1/2 (Co2`, low spin) andS"1 (Ru4`) which gives 3.00 k . Note that this model holds
B
if spin characters are isotropic as mentioned previously.

FIG. 10. Temperature dependence of magnetic susceptibilities M/H at
H"0.5 T for Ca Co Ru O . Solid marks represent ZFC, and open
3 1`x 1~x 6marks represent FC. For (x40.5), only ZFC process are presented. Inset:
Enlarged plot for 04x40.5.

We have prepared the new series of one-dimensionaloxides Ca Co B O (B"Ir, Ru) isostructural with
3 1`x 1~x 6
Sr ZnIrO . Ca CoIrO shows the abrupt drop in the mag3
6
3
6
netic susceptibility at 30 K, as in the case of Sr NiIrO ,3
6suggesting that the ferromagnetic chains couple antiferromagnetically. On the contrary, Ca CoRuO is an ordinary3
6
antiferromagnet with ¹ "55 K. For the further underN
standing of the magnetism on these compounds, the comparison with other Ir- and Ru-based compounds would be
important. We have succeeded in preparing a new Ir-based
compound Sr CoIrO , whose structure and magnetic
3
6
properties will be published elsewhere. Attempts to synthesize other Ru-based compounds such as Ca NiIrO ,36
Sr CoRuO , and Sr ZnRuO were all unsuccessful.
36
3
6REFERENCES
1. A. P. Wilkinson, A. K. Cheetham, W. Kunnman, and As . Kvick, Eur. J.
Solid State Inorg. Chem. 28, 453 (1991).
2. G. Bergerhoff and O. Schmitz-Dumott, Z. Anorg. Allg. Chem. 284, 10(1956).
3. J. L. Hodeau, H. Y. Tu, P. Bordet, T. Fournier, P. Strobel, M. Marezio,
and G. V. Chandrashekhar, Acta Cryst. B48, 1 (1992).
4. T. N. Nguyen, D. M. Giaquinta, and H.-C. zur Loye, Chem. Mater. 6,1642 (1994).
5. T. N. Nguyen and H. C. zur Loye, J. Solid State Chem. 117, 300 (1995).
6. T. N. Nguyen, P. A. Lee, and H.-C. zur Loye, Science 271, 489 (1996).
7. N. Segal, J. F. Vente, T. S. Bush, and P. D. Battle, J. Mater. Chem. 6,
395 (1996).
8. C. Lampe-O®nnerud, M. Sigrist, and H.-C zur Loye, J. Solid State Chem.
127, 25 (1995).
9. H. Fjellva> g, E. Gulbrandsen, S. Aasland, A. Oslen, and B. C. Haucack,J. Solid State Chem. 124, 190 (1996).
10. J. Darriet, F. Grasset, and P. D. Battle, Mater. Res. Bull. 32, 139(1997).
11. S. Aasland, H. Fjellva> g, and B. Hauback, Solid State Commun. 101, 187(1997).
12. H. Kageyama, J. Yoshimura, K. Kosuge, H. Mitamura, and T. Goto,
J. Phys. Soc. Jpn. 66, 1607 (1997).
13. H. Kageyama, K. Yoshimura, K. Kosuge, M. Azuma, M. Takano,
H. Mitamura, and T. Goto, J. Phys. Soc. Jpn. 66, 3996 (1997).
14. H. Kageyama, S. Kawasaki, K. Mibu, M. Takano, K. Yoshimura, andK. Kosuge, Phys. Rev. ¸ett. 79, 3258 (1997).
15. E. Wocrmann and A. Muan, J. Inorg. Nucl. Chem. 32, 1457 (1970).
16. H. M. Rietveld, J. Appl. Crystallogr. 2, 65 (1969).
17. F. Izumi, ‘‘The Rietveld Method’’ (R. A. Young, Ed.). Oxford University Press, Oxford (1993), Chap. 13; Y.-I. Kim and F. Izumi, J. Ceram.
Soc. Jpn. 102, 401 (1994).