1. Art and Diseño

Journal of Alloys and Compounds 354 (2003) 95–98
L
www.elsevier.com / locate / jallcom
Structure, magnetic susceptibility and resistivity properties of SrVO 3
Y.C. Lan*, X.L. Chen, M. He
Institute of Physics and Centre for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080, PR China
Received 7 February 2002; received in revised form 20 November 2002; accepted 26 November 2002
Abstract
The crystallographic structure of the compound SrVO 3 has been determined by X-ray diffraction and refined by the Rietveld method.
˚ space group Pm3¯m, Z51. The electrical
The structural analysis suggest SrVO 3 presents a cubic perovskite structure with a53.8425(1) A,
resistivity measurement suggests metallic behavior for the oxide. Magnetic susceptibility measurement confirms that some trace impurities
are still present in the nearly single phase specimen and affect the magnetic behavior of the samples.
 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structure; X-ray diffraction; Electrical transport
1. Introduction
Strontium vanadate (SrVO 32d ) was first synthesized in
the 1950s [1] and reported to be a cubic perovskite with a
˚ d 50–0.5 [2–4]. The
cell parameter a53.840–3.849 A,
oxide is a member of a family of metallic transition-metal
(TM) oxides with the layered perovskite structure. Therefore SrVO 32d has been investigated as an ideal case for
investigating the anomalous metallic properties near the
Mott transition [5–7]. After the discovery of superconductivity in perovskite-like cuprate oxides [8], it is recognized
[9,10] that the electronic configuration of V 41 with one 3d
electron is analogous to the configuration (3d 9 ) of Cu 21
which has one 3d hole. Because of the above 3d 1 electronic configuration and its perovskite-like structure,
SrVO 32d has been widely investigated during the 1990s
[10–16] to search for new superconductors. Up to now,
most research has indicated that the material shows a Pauli
paramagnetic character and metallic behavior near room
temperature. Additionally, the oxide is also a potential
oxide electrical conductor [17,18] and has been given more
attention in recent years.
However it is very difficult to obtain a homogeneous,
single-phase stoichiometric specimen because the Sr / V
stoichiometry is fairly unstable [5] in the preparation
*Corresponding author. Department of Physics, Temple University,
Philadelphia, PA 19122, USA. Tel.: 11-215-204-7887; fax: 11-215-2045652.
E-mail address: [email protected] (Y.C. Lan).
process (an inert or reducing environment is always
required). Small amount of impurities, such as Sr 8 V8 O 25
and other vanadium oxides, are still present in the specimens. The oxygen content is not easily controlled either.
Therefore, the crystallographic structure was determined
roughly. In this present work, we carefully synthesized
good quality SrVO 32d specimens and determined the
crystallographic structure. Electrical resistivity and magnetic susceptibility are also measured. Here we report the
crystallographic study as well as the electrical and magnetic investigations of the compound SrVO 32d .
2. Experimental
Samples were prepared by a solid-state reaction method
using SrCO 3 (Alfa, 99.9% pure) and V2 O 5 (99.9% pure)
powders as starting materials. The powders were mixed
and ground stoichiometrically. The green mixture was
calcined at 700 8C in air for 2 days with intermediate
grindings. X-ray powder diffraction showed that the product at this stage contained Sr 3 V2 O 8 as an impurity phase.
The calcined samples were reduced several times at
1000 8C in a flowing hydrogen atmosphere (|20 cc / min)
with intermittent grinding and pelleting, and finally
quenched to room temperature in protective ambience.
Every time after the intermittent grinding, the reduced
products were conveniently checked by examining X-ray
diffraction patterns in order to avoid too much reduction.
The process was repeated until no hexagonal compound
0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved.
doi:10.1016 / S0925-8388(02)01349-X
Y.C. Lan et al. / Journal of Alloys and Compounds 354 (2003) 95–98
96
Sr 8 V8 O 25 and other impurities can be determined from
X-ray diffraction. The color of the sample turned to black
after the completion of reduction. Some reduced sample
tablets were directly used for electrical resistivity measurements or ground to powder for X-ray diffraction measurements.
The crystal structure and the lattice constants of the
reduced samples were determined by X-ray diffraction at
room temperature using Cu Ka radiation on a Rigaku
diffractometer equipped with the curved graphite monochromator. Silicon powder was used as an internal standard to determine the lattice parameters. The data were
collected in the step scanning mode with steps of 0.028
(2u ). An angular range from 2u 520–1358 and a measuring time of 1 s / step were applied. The divergence,
scattering, and receiving slits were set at 18, 18 and 0.1
mm, respectively. A total of 5751 points with a maximum
count of 31 544 and 19 independent reflections were
measured. The lattice parameters were calculated with the
program TREOR90 [19]. The structure was refined by the
Rietveld refinement method [20].
Electrical resistivity was measured in the temperature
range of 4.2–300 K using a standard dc four-probe
technique and the magnetic properties were studied with a
commercial SQUID magnetometer.
3. Results and discussions
3.1. Crystal structure
The observed powder diffraction data of SrVO 32d are
given in Table 1. Interplanar spacings, hkl indices and
Table 1
˚ room temperature
X-ray powder diffraction data. l 51.5406 A,
2u
(8)
I /I0
d
˚
(A)
hkl
23.12
32.93
40.62
47.26
53.26
3
100
20
45
3
3.844
2.718
2.2192
1.9218
1.7185
1
1
1
2
2
58.81
69.08
73.94
78.68
83.34
40
25
2
16
5
1.5689
1.3586
1.2808
1.2151
1.1586
211
220
300,221
310
311
87.96
92.58
97.20
106.62
111.48
7
1
18
4
2
1.1093
1.0656
1.0269
0.9606
0.9320
222
320
321
400
410,322
116.54
121.82
127.42
133.45
10
3
10
1
0.9057
0.8815
0.8592
0.8385
330,411
331
420
421
0
1
1
0
1
0
0
1
0
0
relative intensities are also listed. The main diffraction
peaks can be indexed using a cubic cell with lattice
˚ (the figure of merit [21]
parameter a53.8425(1) A
F(19)5106). The oxygen stoichiometry of the oxide was
studied by thermogravimetric analysis (TGA), oxidizing
the sample at 1100 8C in air. The oxygen content 32d of
the obtained SrVO 32d samples is 3.00 within an experimental error of 60.05.
The nearly single phase presents a structure isotypic
with the so-called compounds SrVO 2.5 [1] and SrVO 2.88
[3]. The observed condition for reflection allows for the
¯ m, Pm3¯ and P23. Starting with
space groups Pm3¯m, P43
¯
Pm3m, the Sr and V atoms were located on the site
1a(0,0,0) and 1b(0.5,0.5,0.5), respectively, according to
the ABO 3 cubic perovskite crystallographic structure. The
oxygen atoms were set on the site 3c(0.5,0,0.5). The
occupancy factor for oxygen was also refined.
Using the computer program DBWS-9411 [22], the
Rietveld refinement was carried out. The pseudo-Voigt
function was used for the simulation of the peak shapes
[23]. Intensities within 20 times of the full width at half
maximum were considered to contribute to the reflection.
Peaks below 758 were corrected for asymmetry effects.
The analysis of powder patterns resulted in weak preferred
orientation effects along [011], which was corrected using
the March-Dollase function. The background was refined
by a fifth-order polynomial. At the first step, scattering
factor, zero point, background, profile parameters, and
lattice constant were fitted. Oxygen content in a unit cell
obtained from structural refinement is 3.060.1, which
agreed with the experimental measurement from TGA.
Under these conditions, successive refinements of the
positional parameters of oxygen and the isotropic thermal
parameters lead to R wp 57.49%, R exp 54.03%, S51.80.
Attempts with other space groups only yielded larger
agreement factors. Hence, the most probable space group
is Pm3¯m. The results of the refinement are plotted in Fig.
1. Table 2 gives the structure parameters of the final
refinement.
3.2. Electrical and magnetic properties
Fig. 2 shows the temperature dependence of electrical
resistivity r for SrVO 32d . The positive slope with increasing temperature indicates metallic conduction. The resistivity of SrVO 32d was about 41.8 mV?cm at room temperature and slightly decreased to 29.3 mV?cm at 4.2 K. In the
entire temperature range, the electrical resistivity scales
well as T 2 law r 5 r0 1 AT 2 with r0 529.2 mV?cm and
A55.698310 25 mV?cm / K 2 , where T is temperature in
Kelvin. The value of A is in accordance with those
reported for single crystals [3,5]. The electrical resistivity
ratio r300 K /r4.2 K for the sample is around 1.5, which is
much lower than that for the single crystal ( r300 K /r4.2 K |
6) [24]. In the literature, polycrystalline samples always
show a lower resistivity ratio than the single crystal
samples [5,6,11,15]. It is generally accepted that the lower
Y.C. Lan et al. / Journal of Alloys and Compounds 354 (2003) 95–98
97
Fig. 1. The final Rietveld refinement pattern of SrVO 32d . Small crosses represent the experimental values and solid lines the calculated pattern. The solid
line at the bottom is the difference between the experimental and calculated values. The vertical markers show positions calculated for Bragg reflections.
Table 2
Final Rietveld refinement parameters of SrVO 32d from X-ray powder
diffraction data
Atom
Site
x /a
y /b
z /c
˚ 2)
B (A
Sr
V
O
1a
1b
3c
0.0
0.5
0.5
0.0
0.5
0.0
0.0
0.5
0.5
0.6956
0.5323
0.9192
R wp 57.49%, R exp 54.03%.
Fig. 2. Temperature dependence of electric resistivity of SrVO 32d .
resistivity ratio is attributed to the porosity of the polycrystalline specimens. Despite the value of resistivity, all
the samples prepared at different conditions by different
authors show metallic behavior and possess a low electrical resistivity ( r is usually several mV?cm, not higher than
100 mV?cm at room temperature) [3,5,6,11,15,24]. The
non-stoichiometric oxygen has no significant influence on
the metallic properties of the compound.
The temperature dependence of the magnetic susceptibility x is shown in Fig. 3. Susceptibility increases with
decreasing temperature and saturates below 100 K. In other
words, the susceptibility is a constant in the range of
4.2–100 K. This anomalous behavior of the susceptibility
is an intrinsic characteristic of SrVO 3 , probably caused by
the helical magnetic structure as in Co 2 ScSn alloy [25], or
non-intrinsic properties caused by undetected impurities in
the specimens. In order to investigate the origin of the
extraordinary behavior, we measured the DC magnetic
susceptibility up to 2T while increasing and decreasing the
applied magnetic field H at different temperatures, such as
at 4.2, 77 and 300 K. From the isothermal x –H curves, we
found that the total magnetization is attributed to two
terms: paramagnetic moments of SrVO 3 and antiferromagnetic moments of impurities. Below 100 K, with
decreasing temperature, the decreasing susceptibility from
antiferromagnetic impurities counteracts the increasing
susceptibility of the paramagnetic phase, resulting in the
nearly constant susceptibility with temperature. Since
nonstoichiometric V2 O 31x shows a temperature-induced
paramagnetic to antiferromagnetic phase transition in the
10–170 K range (the transition temperature depends on the
oxygen content 31x) [26,27], it is reasonable to suppose
the antiferromagnetic term comes from nonstoichiometric
vanadium oxide impurities which is insufficiently reacted
in the experiment.
98
Y.C. Lan et al. / Journal of Alloys and Compounds 354 (2003) 95–98
Acknowledgements
The authors are very grateful to Dr. C.L. Chen for
valuable discussion about the explanation of the magnetic
properties. The investigations were supported by the
Chinese Academy of Sciences and the National Natural
Science Foundation of China.
References
Fig. 3. Temperature dependence of magnetic susceptibility x of
SrVO 32d .
In the literature, a magnetic anomaly at about 100 K was
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and show paramagnetic behavior, as reported in Refs.
[5,17,29].
4. Conclusion
The nearly single phase SrVO 32d specimens are synthesized carefully through a hydrogen reduction route at
1000 8C. The crystal structure of the compound SrVO 32d
is determined by X-ray powder diffraction and refined
using Rietveld method. It is a cubic perovskite-like struc˚ (the figure of merit F(19)5106)
ture with a53.8425(1) A
¯
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SrVO 32d is metallic in the whole temperature range from
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specimens are single phase samples, magnetic measurements indicates that trace impurities are still present in the
specimens and affect the magnetic properties at low
temperatures. The impurities cause a constant susceptibility in the 4.2–100 K temperature range.
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