9
148 Inorganic Chemistry, Vol. 48, No. 19, 2009
Szajwaj et al.
11-20
21
Finally, Viciu et al. have focused on the
observed.
crucible by chemical reduction of a NaVO
3
powder under a
influence of the sodium content on the structural patterns of
dihydrogen atmosphere at 800 °C for 8 h. NaVO
previously synthesized by the solid-state reaction of a stoi-
chiometric mixture of Na CO (purity above 99.9%) and
3
had been
0
0
P 3-, O3-, and O 3-polytype Na CoO phases (0.3 e x e 0.92).
x
2
0
2
3
The only modulated phase evidenced is O 3-Na0 CoO , with a
.75
2
2 5
V O (purity above 99.9%) by heating it in a platinum
4
D modulation and q=0.33a* - 0.247c*.
crucible up to the melting point. Then, sodium’s extraction
from the NaVO powder was carried out by use of iodine in
In our laboratory, a study of the Na VO (x e 1) system
x
2
2
was recently carried out because interesting electronic prop-
erties could be expected for the partially deintercalated
acetonitrilewithstirringfor1dayatroomtemperature.Then,
the residual powder was washed with acetonitrile, filtered,
and dried under vacuum. Ratios of Na/I varying from 0.30 to
0.42 were tested. The iodine titration of the solution, after the
powderwasremoved, confirmedthatacompletereactionwas
observed until Na/I reached 0.40. The synthesis of the
phases. The structure of NaVO was first reported by
2
::
22
Rudorff and Becker in 1955. The first study of the Na VO2
x
system was performed by Barker and Hooper, who tried to
23
synthesize NaVO by the reaction of liquid sodium on VO .
2
2
Na0.60VO
2
phase has been optimized for the ratio Na/I =
This reaction was difficult to optimize, and they always
0.42. A thermal treatment of the powder at 200 °C under
obtained NaVO mixed with impurities that seemed to be
2
vacuum improves slightly the crystallinity of the powder.
Inductively coupled plasma atomic emission spectrometry
measurements have confirmed the sodium content equal to
0.60(1). Because it is well-known that the transition-metal-
the Na VO partially deintercalated phases. Similar results
x
2
were obtained in 1988 by Chamberland and Porter, who
claimed to obtain two varieties for NaVO : a high-tempera-
2
ture (200 °C) one with rhombohedral symmetry and a room
oxide layer MO is perfectly stoichiometric, one can deduce
2
24
+
3+
4+
temperature one with a lower symmetry. In fact, it seems
that at room temperature they obtained a mixture of the
the formal formula Na 0.60V 0.60V
Powder X-ray diffraction (PXRD) patterns have been
recorded on a Panalitycal X’pert diffractometer operating
0.40 2
O .
NaVO rhombohedral phase with a partially deintercalated
2
˚
˚
with Cu KR radiation (λ = 1.5406 A and λ =1.5444 A) in
1 2
phase and other impurities, which react at 200 °C to form
the range 5° e 2θ e 80°. The powders were put in a specific
airtight holder under dry argon to prevent any reaction with
rhombohedral NaVO . Very recently, Onoda published a
2
very interesting structural and magnetic study on NaVO
2
air moisture. The structural refinement of the PXRD data
The background was
25
26
and on a new P2-Na0.70VO phase. Cava et al. have
27,28
2
was donewithJANA2000 software.
recently investigated the structural and magnetic properties
estimated by a Legendre function, and the peak shapes were
described by a pseudo-Voigt function. Refinement of the
peak asymmetry was performed using the Simpson para-
meter.
of NaVO by a neutron diffraction experiment and have
2
shown, in particular, that a structural and magnetic transi-
tion took place near T=94 K related to an orbital ordering
that retrieves the geometrical frustration.
Electron diffraction has been carried out on a JEOL
2
000FX microscope operating at an accelerating voltage
of 200 kV and equipped with a doubled tilt specimen stage.
A small amount of Na0.60VO was crushed in methanol and
In this paper, we report our results on Na VO with
0
.60
2
0
the P 3-type stacking and an interpretation of its physical
properties.
2
then deposited on a copper grid.
Magnetization measurements were performed using a
superconducting quantum interference device (SQUID)
magnetometer in the 2-300 K temperature range with ap-
plied fields of up to 50 kOe.
Experimental Section
Na VO
x
2
samples (x ≈ 0.60) have been prepared in two
2
steps. First, NaVO samples have been synthesized in a gold
Heat capacity measurements were performed using a qua-
si-adiabatic heat pulse method (Nernst calorimeter). The
powder sampleswere encapsulated inanaluminumfoilunder
a dry argon atmosphere. The heat capacity of the aluminum
foil was subtracted after measurement. The temperature
range for the measurement was 4-200 K.
Electrical direct-current conductivity measurements were
performed with a four-probe method in the 170-300 K range
in a specific sample holder to prevent any reaction with air
moisture.
(
11) Foo, M. L.; Wang, Y.; Watauchi, S.; Zandbergen, H. W.; He, T.;
Cava, R. J.; Ong, N. P. Phys. Rev. Lett. 2004, 92, 247001.
12) Shi, Y. G.; Yang, H. X.; Huang, H.; Liu, X.; Li, J. Q. Phys. Rev. B
006, 73, 094505.
13) Yang, H. X.; Shi, Y. G.; Nie, C. J.; Wu, D.; Yang, L. X.; Dong, C.;
Yu, H. C.; Zhang, H. R.; Jin, C. Q.; Li, J. Q. Mater. Chem. Phys. 2005, 94,
19.
14) Qian, D.; Wray, L.; Hsieh, D.; Wu, D.; Luo, J. L.; Wang, N. L.;
(
2
(
1
(
Kuprin, A.; Fedorov, A.; Cava, R. J.; Viciu, L.; Hasan, M. Z. Phys. Rev.
Lett. 2006, 96, 046407.
(
(
15) Onoda, M.; Ikeda, T. J. Phys.: Condens. Matter 2007, 19, 186213.
16) Huang, Q.; Khaykovich, B.; Chou, F. C.; Cho, J. H.; Lynn, J. W.;
Results and Discussion
Lee, Y. S. Phys. Rev. B 2004, 70, 134115.
17) Huang, Q.; Foo, M. L.; Lynn, J. W.; Zandbergen, H. W.; Lawes, G.;
(
Structural Characterization. From our experiments
on Na CoO phases, in some cases several phases
Wang, Y.; Toby, B. H.; Ramirez, A. P.; Ong, N. P.; Cava, R. J. J. Phys.:
Condens. Matter 2004, 16, 5803.
6
x
2
with very close compositions can exist; therefore, ther-
mal treatment at moderate temperature is a good way
to homogenize the sample. The same behavior is obser-
(
18) Zandbergen, H. W.; Foo, M.; Xu, Q.; Kumar, V.; Cava, R. J. Phys.
Rev. B 2004, 70, 024101.
19) Yang, H. X.; Nie, C. J.; Shi, Y. G.; Yu, H. C.; Ding, S.; Liu, Y. L.;
Wu, D.; Wang, N. L.; Li, J. Q. Solid State Commun. 2005, 134, 403–408.
20) Blangero, M.; Carlier, D.; Pollet, M.; Darriet, J.; Delmas, C.;
Doumerc, J. P. Phys. Rev. B 2008, 77, 184116.
21) Viciu, L.; Bos, J. W.; Zandbergen, H. W.; Huang, Q.; Foo, M. L.;
Ishiwata, S.; Ramirez, A. P.; Lee, M.; Ong, N. P.; Cava, R. J. Phys. Rev. B
(
ved for Na0.60VO , and only thermal treatment at 200 °C
(
2
led us to obtain a single phase. Powder patterns before
and after thermal treatment are shown in Figure 1. The
whole powder pattern of Na0.60VO shown in Figure 2
(
2
2
006, 73, 174104.
::
(22) Rudorff, W.; Becker, U. Z. Naturforsch. 1955, 9b, 613.
(23) Barker, M. G.; Hooper, A. J. J. Chem. Soc., Dalton Trans. 1973, 15,
(27) Petricek, V.; Dusek, M.; Palatinus, L. Jana2000: The Crystallo-
1
517.
(
(
(
24) Chamberland, B. L.; Porter, S. K. J. Solid State Chem. 1988, 73, 398.
graphic Computing System; Institute of Physics: Praha, 2000.
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Rizzi, R. J. Appl. Crystallogr. 1999, 32, 339.
25) Onoda, M. J. Phys.: Condens. Matter 2008, 20, 145205.
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Ronning, F.; Cava, R. J. Phys. Rev. Lett. 2008, 101, 166402.