High-pressure synthesis, crystal structures, and characterization of CdVO3-δ and solid solutions CdVO3-NaVO3

Article abstract of DOI:10.1016/j.jssc.2006.02.018

CdVO_3-δ and solid solutions of Cd_1-xNa_xVO₃ with the GdFeO₃-type perovskite structure were prepared using a high-pressure (6 GPa) and high-temperature technique. No significant oxygen and cation deficiency was found in CdVO₃. Cd_1-xNa_xVO₃ are formed in the compositional range of 0 {less-than or slanted equal to} x {less-than or slanted equal to} 0.2. CdVO₃ and Cd_1-xNa_xVO₃ demonstrate metallic conductivity and Pauli paramagnetism between 2 and 300 K. A large electronic contribution to the specific heat ( γ = 13.4 and 11.2 mJ / ( mol K²) for CdVO₃ and Cd_0.8Na_0.2VO₃, respectively) was observed at low temperatures due to the strongly correlated electrons. Crystal structures of CdVO₃ and Cd_0.8Na_0.2VO₃ were refined by X-ray powder diffraction: space group Pnma; Z = 4; a = 5.33435 ( 7 ) A, b = 7.52320 ( 9 ) A, and c = 5.26394 ( 6 ) A for CdVO₃ and a = 5.32056 ( 9 ) A, b = 7.50289 ( 13 ) A, and c = 5.25902 ( 8 ) A for Cd_0.8Na_0.2VO₃.

Full text of DOI:10.1016/j.jssc.2006.02.018

ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 1650–1658
www.elsevier.com/locate/jssc
High-pressure synthesis, crystal structures, and characterization of
CdVO3ꢀd and solid solutions CdVO3–NaVO3
Ã
Alexei A. Belika, , Eiji Takayama-Muromachib
aInternational Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
bAdvanced Materials Laboratory (AML), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Received 18 November 2005; received in revised form 31 January 2006; accepted 15 February 2006
Available online 6 March 2006
Abstract
CdVO3ꢀd and solid solutions of Cd1ꢀxNaxVO3 with the GdFeO3-type perovskite structure were prepared using a high-pressure
(6 GPa) and high-temperature technique. No significant oxygen and cation deficiency was found in CdVO3. Cd1ꢀxNaxVO3 are formed in
the compositional range of 0pxp0:2. CdVO3 and Cd1ꢀxNaxVO3 demonstrate metallic conductivity and Pauli paramagnetism between 2
and 300 K. A large electronic contribution to the specific heat (g ¼ 13:4 and 11:2 mJ=ðmol K2) for CdVO3 and Cd0.8Na0.2VO3,
respectively) was observed at low temperatures due to the strongly correlated electrons. Crystal structures of CdVO3 and Cd0.8Na0.2VO3
˚
˚
˚
were refined by X-ray powder diffraction: space group Pnma; Z ¼ 4; a ¼ 5:33435ð7Þ A, b ¼ 7:52320ð9Þ A, and c ¼ 5:26394ð6Þ A for
˚
˚
˚
CdVO3 and a ¼ 5:32056ð9Þ A, b ¼ 7:50289ð13Þ A, and c ¼ 5:25902ð8Þ A for Cd0.8Na0.2VO3.
r 2006 Elsevier Inc. All rights reserved.
Keywords: High-pressure synthesis; GdFeO3; Perovskite; Resistivity; Magnetic susceptibility; Specific heat; Crystal structures
1. Introduction
structure [10] while CaVO3 has the GdFeO3-type perovs-
kite structure (space group Pnma; lattice parameters
˚
˚
˚
Transition-metal perovskites, ABO3, have attracted
much attention because of their interesting electronic and
magnetic properties arising from narrow 3d bands, strong
Coulomb correlations, and highly correlated d electrons.
The 3d1 (B ¼ Ti3+ and V4+) perovskites are particularly
interesting because similar materials have very different
electronic properties, and they do not show a complicated
electronic structure [1].
Ca1ꢀxSrxVO3, as a strongly correlated d1-electron
system, has been investigated a lot [1–9]. Transport and
magnetic properties of SrVO3 are typical for a conven-
tional Fermi liquid [10,11]. CaVO3 has been reported to be
metallic and insulating, Pauli paramagnetic and Curie–
Weiss paramagnetic. This large variation in properties of
CaVO3 reflects problems with the oxygen content [12].
Contradictory results on spectral, transport, and thermo-
dynamic properties are also reported for Ca1ꢀxSrxVO3
[1–9]. SrVO3 crystallizes in a simple cubic perovskite
a ¼ 5:3171 A, b ¼ 7:5418 A, and c ¼ 5:3396 A) [13].
In addition to the extensively studied CaVO3 [13–15] and
SrVO3 [10,11], whose properties are usually investigated
together [1–9,16,17], other oxides are known with the
formula of A2+V4+O3, e.g., BaVO3 [18], PbVO3 [19,20],
and ambient- and high-pressure modifications of CdVO3
[21,22]. The high-pressure modification of CdVO3, HP-
CdVO3, was reported to have the GdFeO3-type perovskite
structure [22], but the crystal structure of HP-CdVO3 has
not been investigated yet. Down to 77 K, HP-CdVO3
demonstrated metallic conductivity and Pauli paramagnet-
ism similar to the stoichiometric CaVO3. Note that the
ambient-pressure modification of CdVO3 crystallizes in
˚
˚
space group Pnma with a ¼ 14:301 A, b ¼ 3:598 A, and c ¼
4+
˚
5:204 A [21], and V ions are located in VO5 pyramids in
comparison to the usual octahedral coordination of B-type
ions in the perovskite-type structures. Despite the fact that
CaVO3 and HP-CdVO3 are isotypic, there are no reports,
to the best of our knowledge, about HP-CdVO3 except for
Refs. [22,23]. However, spectral, transport, and magnetic
properties of HP-CdVO3 and solid solutions including it as
Ã
Corresponding author. Fax: +81 029 860 4706.
E-mail address: Alexei.BELIK@nims.go.jp (A.A. Belik).
0022-4596/$ - see front matter r 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2006.02.018

ARTICLE IN PRESS
A.A. Belik, E. Takayama-Muromachi / Journal of Solid State Chemistry 179 (2006) 1650–1658
1651
the end member appear to be interesting in the same
manner as those of CaVO3.
2.5. XRD experiments and structure refinements
In this work, we report on CdVO3ꢀd and solid solutions
of Cd1ꢀxNaxVO3 prepared at high pressure. Crystal
structures of HP-CdVO3 and Cd0.8Na0.2VO3 were studied
by X-ray powder diffraction (XRD). Basic physical
properties of CdVO3ꢀd and Cd1ꢀxNaxVO3 were investi-
gated.
XRD data for phase analysis and structure refinement
were collected at RT on a RIGAKU Ultima III diffract-
ometer using CuKa radiation. The measurement time was
1 s/step for phase analysis, and 10 s/step for structure-
refinement data sets (a step width of 0.021). The XRD data
were analyzed by the Rietveld method with RIETAN-2000
[24]. Coefficients for analytical approximation to atomic
scattering factors for Cd, Na, V, and O were taken from
[25]. The split pseudo-Voigt function of Toraya [26] was
used as a profile function. The background was represented
by an nth-order Legendre polynomial. Isotropic atomic
displacement parameters, U, with the isotropic De-
byeꢀWaller factor represented as exp(ꢀ8p2U sin2y/l2)
were assigned to all the sites. The known impurities were
taken into account during the refinements. For the known
impurity phases, we refined only scale factors and lattice
parameters, fixing their structure parameters. The mass
fractions of impurities in the samples were calculated from
the scale factors refined in their Rietveld analyses.
2. Experimental section
2.1. Synthesis
Samples with the nominal compositions of Cd0.9VO3 and
CdVO3ꢀd (d ¼ ꢀ0:1; 0:0; 0:1; 0:2; 0:5) and solid solutions of
Cd1ꢀxNaxVO3 (0pxp0:4) were prepared from stoichio-
metric mixtures of CdO (99.9%), V2O3, V2O5 (99.9%), and
NaVO3. The mixtures were placed in Au capsules and
treated in a belt-type high-pressure apparatus at 6 GPa and
1273 K for 60ꢀ90 min. After heat treatment, the samples
were quenched to room temperature (RT), and the pressure
was slowly released. Single-phased V2O3 was obtained by
reducing V2O5 in a mixture of 10% H2+90% N2 at 1073 K
for 4 h. Single-phased NaVO3 was synthesized in air from
V2O5 and Na2CO3 (99.9%) at 803 K for 90 h with several
intermediate grindings.
3. Results and discussion
3.1. Phase compositions of CdVO3ꢀd and Cd1ꢀxNaxVO3
XRD showed that the samples with the nominal
composition of Cd0.9VO3 and CdVO3.1 contained a
GdFeO3-type phase and strong unidentified reflections
(the strongest ones at 2y ¼ 30:851, 31.001, and 35.901:
phase I). This fact indicates that CdVO3 does not have
significant cation deficiency. The samples with the nominal
2.2. Scanning electron microscopy (SEM) and energy
dispersive X-ray (EDX) analysis
SEM–EDX analysis was performed using a Hitachi S-
4800 scanning electron microscope, equipped with an EDX
spectrometer (Horiba, EMAX).
composition of CdVO2.5 and CdVO2.8 contained
a
GdFeO3-type phase and impurities of CdO, CdCO3, and
an unidentified phase II (with the strongest reflections at
2y ¼ 19:201, 25.521, and 33.601). The formation of the
GdFeO3-type phase in CdVO2.5 suggests that V3+ is
oxidized to V4+ in the bulk of the sample due to the
reduction of CdO to metal Cd on the surfaces:
2.3. Thermal analysis
The thermal stability was examined in air on a SII Exstar
6000 (TG-DTA 6200) system. CdVO3 and Cd0.8Na0.2VO3
were heated up to 1093 and 993 K, respectively, at a
heating–cooling rate of 10 K/min in Pt holders.
3CdO þ V2O3 ¼ 2CdVO3 þ Cd ðin AuÞ:
(1)
When the sample with the nominal composition of
CdVO2.5 was treated at 6 GPa and a higher temperature of
1473 K, it contained only a GdFeO3-type phase, VO2, and
a phase having the structure of Au with very broad
reflections. The formation of VO2 in this case clearly
confirmed the following reaction:
2.4. Physical properties measurements
Direct current (dc) magnetic susceptibilities (w ¼ M=H)
were measured on a Quantum Design SQUID magnet-
ometer (MPMS XL) between 1.8 and 300 K in an applied
field of 100 Oe (1 Oe ¼ (103/4p) A/m) under both zero-field-
cooled (ZFC) and field-cooled (FC) conditions. Isothermal
magnetization curves were recorded at 2 K in applied fields
from ꢀ70 to 70 kOe. Specific heat, Cp, was recorded
between 1.8 and 100 K on cooling at zero magnetic field by
a pulse relaxation method using a commercial calorimeter
(Quantum Design PPMS). Electrical resistivity was mea-
sured between 2 and 300 K by the conventional four probe
method using a Quantum Design PPMS with the ac-gage
current of 1 mA at 30 Hz.
2CdO þ V2O3 ¼ CdVO3 þ VO2 þ Cd ðin AuÞ.
(2)
Reactions (1) and (2) may also occur in the samples with
the nominal compositions of CdVO2.9 and CdVO2.8
changing to some extent the oxygen content of the
GdFeO3-type phases and oxidizing V ions in the bulk of
the samples. The surface of the pellets was usually strongly
attached to Au capsules and removed with the capsules.
This is why we could not detect metal Cd or Au in the bulk

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1652
of the CdVO2.9, CdVO2.8, and CdVO2.5 samples treated at
1273 K.
Note that when the sample with the nominal composi-
tion of CdVO2.8 was prepared at 1273 K using BN between
the Au capsule and the sample, no GdFeO3-type phase was
found. This sample contained CdO and phase II. On the
other hand, CdVO3 could be prepared using BN between
the Au capsule and the sample. These facts show the
importance of Au in the formation of the GdFeO3-type
phases in the samples with the nominal composition of
CdVO3ꢀd with d40.
XRD showed that the solid solutions of Cd1ꢀxNaxVO3
are formed in the compositional range of 0pxp0:2; even
small amount of impurities VO2 and CdCO3 were found in
these samples. These impurities correspond to the starting
reagents. In the XRD patterns of the samples with x ¼ 0:3
and 0.4, additional reflections of unidentified impurities
were observed.
Fig. 2. Typical SEM image of the polished pellet of Cd0.8Na0.2VO3. The
EDX results from the region shown by the solid-line rectangle are
(Cd+Na)/V ¼ 1.01 and Cd/Na ¼ 0.25.
Figs. 1 and 2 display typical SEM images of polished
pellets of CdVO3 and Cd0.8Na0.2VO3. The local EDX
analysis showed that the Cd/V ratio in CdVO3 varied
between 0.99 and 1.04 with the average value of 1.00,
confirming the cation stoichiometry of the obtained CdVO3
sample. In Cd0.8Na0.2VO3, the (Cd+Na)/V ratio was
between 1.01 and 1.04 (the average value was 1.02), and
the Cd/Na ratio between 0.22 and 0.26 (the average value
was 0.24). These results confirmed the cation composition
of Cd0.8Na0.2VO3.
The thermal analysis showed that CdVO3 and
Cd0.8Na0.2VO3 started to be oxidized in air from about
773 and 673 K, respectively. The weight gain of CdVO3 was
3.6% that is close to the theoretical value of 3.8%. The
weight gain of Cd0.8Na0.2VO3 was 3.1% that is close to the
theoretical value of 3.3%. According to XRD, the final
products of the oxidation were Cd2V2O7 for CdVO3 and
Cd2V2O7+NaVO3 for Cd0.8Na0.2VO3. Note that for the
composition of Cd0.8Na0.2V4+O2.9, a noticeably larger
weight gain would be expected (4.2%). Therefore, the
results of thermogravimetry confirmed the oxygen content
of the obtained CdVO3 and Cd0.8Na0.2VO3 samples.
The lattice parameters of the GdFeO3-type phase in all
the samples Cd0.9VO3 and CdVO3ꢀd were similar to each
other (Table 1). The structure analysis of the sample with
the nominal composition of CdVO2.8 using XRD revealed
no evidence for oxygen deficiency. The thermal analysis
showed that the weight gain of the sample with the nominal
composition of CdVO2.8 was 3.7% that is close to that of
CdVO3. However, for the real composition of CdVO2.8, the
weight gain would be 5.4%. These facts support the idea
that the composition of the GdFeO3-type phases in the
CdVO3ꢀd samples with d40 was almost the same without
significant oxygen deficiency.
3.2. Structure refinements of CdVO3 and Cd0.8Na0.2VO3
Fig. 1. Typical SEM images of the polished pellet of CdVO3. The EDX
results from the region shown by the solid-line rectangle are Cd/V ¼ 1.00.
The dotted-line rectangle shows the inclusion of the impurity of VO2.
The XRD patterns of CdVO3 and Cd0.8Na0.2VO3 were
found to be very similar to those of GdFeO3-type

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1653
Table 1
Synthesis conditions, phase compositions, and lattice parameters of the GdFeO3-type phases
Nominal composition
Synthesis conditionsa
Impurities (mass fraction)b
Lattice parameters of the GdFeO3-type phase
CdVO3
CdVO2.9
1273 K, Au
1273 K, Au
1273 K, Au
1273 K, BN
1273 K, Au
1473 K, Au
1273 K, Au
1273 K, Au
1273 K, Au
1273 K, Au
1273 K, Au
1273 K, Au
VO2 (1%), CdCO3 (o1%)
CdO (1%), CdCO3 (1%)
CdO (3%), CdCO3 (2%), phase II (tr)
CdO, phase II (st)
5.3344
7.5232
5.2639
5.3371(1)
5.3371(1)
—
7.5267(2)
7.5268(2)
—
5.2661(1)
5.2655(1)
—
CdVO2.8
CdVO2.8
CdVO2.5
CdVO2.5
CdO (2%), CdCO3 (2%), phase II (w)
VO2 (13%), Au–Cd alloy (24%)
Phase I (st)
5.3344(2)
5.3358(2)
5.3371(3)
5.3376(3)
5.3290(2)
5.3206
7.5229(3)
7.5249(2)
7.5270(4)
7.5258(4)
7.5156(2)
7.5029
5.2622(2)
5.2629(2)
5.2675(3)
5.2670(3)
5.2644(2)
5.2590
CdVO3.1
Cd0.9VO3
VO2 (2%), CdCO3 (3%), phase I (st)
VO2 (1%), CdCO3 (2%)
VO2 (1%), CdCO3 (3%)
Unknown
Cd0.9Na0.1VO3
Cd0.8Na0.2VO3
Cd0.7Na0.3VO3
Cd0.6Na0.4VO3
5.3160(3)
5.2963(5)
7.4987(5)
7.5507(7)
5.2599(3)
5.2839(5)
Unknown
aSynthesis temperature and a material surrounding the sample.
btr: traces, w: weak reflections, st: strong reflections.
compounds. Therefore, for initial fractional coordinates in
Rietveld analysis of CdVO3 and Cd0.8Na0.2VO3, we used
those of CaVO3 with space group Pnma [13].
Table 2
Conditions of the diffraction experiments and parts of refinement results
for CdVO3 and Cd0.8Na0.2VO3
The refinement of occupancy, g, of the Cd site in CdVO3
resulted in g(Cd) ¼ 1.005(4). The refinement of the g value
for the Cd/Na site in Cd0.8Na0.2VO3 when only Cd was
included resulted in g(Cd) ¼ 0.843(4). However, for the
virtual atom VA ¼ 0.8Cd+0.2Na, g(VA) ¼ 1.001(4).
Therefore, the structural data confirmed that a part of
Cd was replaced by Na in Cd0.8Na0.2VO3.
Table 2 gives experimental and refinement conditions,
lattice parameters, R factors, and so forth. Final fractional
coordinates and U parameters for CdVO3 and Cd0.8Na0.2
VO3 are listed in Table 3, and selected bond lengths, l, and
angles, f, calculated with ORFFE [27] in Table 4. Fig. 3
displays observed, calculated, and different XRD patterns.
To obtain information on formal oxidation states of Cd
and V, we calculated the bond valence sums, BVS [28], of
the Cd and V sites in CdVO3 from the Cd–O and V–O
bond lengths. The resulting BVS values were 2.08 for Cd
and 4.03 for V (Table 4). These BVS values support the
oxidation states of +2 and +4 for Cd and V, respectively.
The V–O bond lengths of Cd0.8Na0.2VO3 were slightly
shorter than those of CdVO3 in agreement with the
presence of V5+ in Cd0.8Na0.2VO3.
CdVO3
Cd0.8Na0.2VO3
2y range; step (deg)
Number of data points
Space group
18ꢀ148.4; 0.02
15ꢀ140; 0.02
6521
Pnma (No. 62)
6251
Pnma (No. 62)
Z
4
4
Lattice parameters:
˚
a (A)
5.33435(7)
7.52320(9)
5.26394(6)
211.249(5)
232
5.32056(9)
7.50289(13)
5.25902(8)
209.938(6)
216
˚
b (A)
˚
c (A)
3
V (A )
˚
Number of Bragg reflections
Number of some variablesa
Background; Profiles
Structure (x, y, z, U)
Rwp (%); Rp (%)
8; 7
11
10; 7
10
8.83; 6.54
3.18; 1.88
1.67
9.89; 7.76
5.24; 2.94
1.87
RB (%); RF (%)
S ¼ Rwp/Re
aOther variables include zero shifts, scale factors, and lattice para-
meters.
boundaries, and specific distribution of impurities, for
example, in grain boundaries. The pellets of CdVO3 and
especially Cd0.8Na0.2VO3 were rather porous (Figs. 1 and 2).
This fact can explain the large absolute values of resistivity
of CdVO3 and Cd0.8Na0.2VO3. Even the absolute values of
resistivity of polycrystalline samples may differ from those
of single-crystals samples, the qualitative temperature de-
pendence of resistivity of polycrystalline samples reflects the
intrinsic properties. Note that the samples with the nominal
compositions of CdVO2.9 and CdVO2.8 had r300 ꢁ 0:0025
and 0.0058O cm, respectively, probably due to the better
contacts between grains.
3.3. Physical properties
CdVO3 and Cd0.8Na0.2VO3 showed metallic-like resis-
tivity in the whole temperature range. That is, the
resistivity decreased almost linearly with decreasing tem-
perature (Fig. 4). The resistivity at 300 K (r300) was about
0.4 O cm in CdVO3 and 0.7 O cm in Cd0.8Na0.2VO3. These
values are much larger than those of typical metals, such as
single crystals of SrVO3 [5], but comparable with the
reported values of polycrystalline samples of SrVO3
(r300E0.4 O cm [10]), CaVO3 (r300E35 O cm [13]), and
HP-CdVO3 (r300E1 O cm [22]). This is attributed to the
porosity of polycrystalline samples, effects of grain
CdVO3 and Cd0.8Na0.2VO3 exhibited Pauli paramag-
netic behavior of magnetic susceptibility. That is, magnetic
susceptibilities were almost constant in a wide temperature

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1654
Table 3
Structure parameters for CdVO3 and Cd0.8Na0.2VO3
a
2
10 U (A )
2
Siteb
Wyckoff position
x
y
z
˚
Cd
Cd/Nac
V
4c
0.03536(10)
0.03288(18)
0.25
0.25
0
ꢀ0.0072(2)
ꢀ0.0058(4)
0.5
0.89(2)
0.53(3)
0.61(3)
0.57(4)
4b
4c
8d
0
0
0
0.5
O1
O2
0.4762(10)
0.4774(15)
0.25
0.25
0.0882(10)
0.0792(16)
0.8(2)
1.0(3)
0.2884(9)
0.2928(14)
0.0439(6)
0.0391(9)
0.7075(8)
0.7074(13)
0.84(13)
¼ U (O1)
aThe first (x, y, z, and U) line of each site is for CdVO3, and the second one for Cd0.8Na0.2VO3.
bOccupancies of all the sites are unity.
cCd/Na: g(Cd) ¼ 0.8 and g(Na) ¼ 0.2.
Table 4
Bond lengths, l (A), angles, f (deg), and bond valence sums, BVS [28], in CdVO3 and Cd0.8Na0.2VO3
a
˚
CdVO3
Bonds
Cd0.8Na0.2VO3
Bonds
l
l
Cd–O1
Cd–O2 ( ꢂ 2)
Cd–O1a
2.228(6)
2.291(4)
2.405(5)
2.546(5)
2.655(5)
3.025(6)
3.074(6)
2.08
Cd/Na–O1
Cd/Na–O2 ( ꢂ 2)
Cd/Na–O1a
2.263(9)
2.294(6)
2.407(8)
2.587(8)
2.612(8)
2.989(8)
3.030(9)
2.05
Cd–O2a ( ꢂ 2)
Cd–O2b ( ꢂ 2)
Cd–O1b
Cd/Na–O2a ( ꢂ 2)
Cd/Na–O2b ( ꢂ 2)
Cd/Na–O1b
Cd–O1c
Cd/Na–O1c
BVS(Cd/Na) with R0 (Cd2+
V–O2 ( ꢂ 2)
BVS(Cd) with R0(Cd2+
V–O2 ( ꢂ 2)
V–O2a ( ꢂ 2)
V–O1 ( ꢂ 2)
)
)
1.916(5)
1.937(5)
1.941(2)
4.03
1.916(7)
1.924(7)
1.925(2)
4.14
V–O2a ( ꢂ 2)
V–O1 ( ꢂ 2)
BVS(V) with R0(V4+
)
BVS(V) with R0(V4+
)
Angles
f
Angles
f
O1–V–O1
180
180
O1–V–O1
180
180
O2–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O2–V–O2 ( ꢂ 2)
O2–V–O2 ( ꢂ 2)
V–O1–V
O2–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O1–V–O2 ( ꢂ 2)
O2–V–O2 ( ꢂ 2)
O2–V–O2 ( ꢂ 2)
V–O1–V
88.8(1)
88.6(1)
90.6(1)
91.4(1)
89.4(1)
89.3(1)
90.7(1)
154.0(1)
153.9(1)
90.8(1)
91.2(1)
89.2(1)
89.2(1)
90.8(1)
151.3(1)
153.1(1)
V–O2–V ( ꢂ 2)
V–O2–V ( ꢂ 2)
P
aBVS ¼ ni, ni ¼ exp[(R0ꢀli)/B], B ¼ 0.37, R0(Cd2+) ¼ 1.904, and R0(V4+) ¼ 1.784.
range with an upturn at low temperatures due to the
presence of paramagnetic impurities or defects (Fig. 5).
Almost no difference was found between the curves
measured under the ZFC and FC conditions.
constant. The aT2 term is considered to originate from the
higher-order temperature-dependent term in the Pauli para-
magnetism that is neglected in the zero-order approximation.
This term reflects the shape of the density of states at the
Fermi level. The fit to Eq. (3) in the whole tem-
perature ranges resulted in w0 ¼ 2:945ð5Þ ꢂ 10ꢀ4 cm3=mol,
Cimp ¼ 4:63ð8Þ ꢂ 10ꢀ4 cm3 K=mol, yimp ¼ ꢀ0:01ð4Þ K, and
a ¼ 3:76ð11Þ ꢂ 10ꢀ10 cm3=ðK2 molÞ for CdVO3 and w0 ¼
The w(T) curves could be fit with the following equation [5]:
wðTÞ ¼ w0 þ Cimp=ðT ꢀ yimpÞ þ aT2,
(3)
where w0 is the temperature-independent term including the
diamagnetic and Pauli paramagnetic contributions, Cimp is
the impurity Curie constant, and yimp is the impurity Weiss
2:968ð7Þ ꢂ 10ꢀ4 cm3=V4þꢀmol,
Cimp ¼ 9:62ð11Þ ꢂ 10ꢀ4
cm3 K=V4þꢀmol, yimp ¼ ꢀ0:22ð3Þ K, and a ¼ 2:3ð2Þ ꢂ

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1655
8
CdVO3
24
16
8
4
0
-4
-8
20
30
40
50
0
-8
21
6
0
Cd0.8 Na0.2VO3
14
7
-6
20
30
40
50
0
-7
40
20
60
80
100
120
140
2ꢀ (deg)
Fig. 3. Observed (crosses) and calculated (solid line) XRD patterns for CdVO3 and Cd0.8Na0.2VO3. The difference pattern is shown at the bottom. Bragg
reflections are indicated by tick marks for the GdFeO3-type phase (upper), CdCO3 (middle), and VO2 (lower). Insets show the enlarged fragments.
0.8
Cd0.8Na0.2VO3
0.6
0.4
CdVO3
0.2
0.0
0
50
100
150
200
250
300
Temperature (K)
Fig. 4. Temperature dependence of the resistivity of CdVO3 (circles) and Cd0.8Na0.2VO3 (squares) measured at 1 mA.
10ꢀ10 cm3=ðK2V4þꢀmolÞ for Cd0.8Na0.2VO3. The w0 values of
CdVO3 and Cd0.8Na0.2VO3 were close to those of CaVO3 and
SrVO3 [5,13], taking into account the fact that the
diamagnetic contribution is usually one order of magnitude
smaller than the obtained w0 values. From the Cimp values, we
can estimate that only 0.12% and 0.26% of the V sites have

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1656
0.0008
Cd0.8Na0.2VO3
0.0006
0.0004
CdVO3
0.0002
0.0000
0
50
100
150
200
250
300
Temperature (K)
Fig. 5. Temperature dependence of the magnetic susceptibilities of CdVO3 (circles) and Cd0.8Na0.2VO3 (squares) measured at 100 Oe. The solid lines are
the fits to Eq. (3) with the parameters given in the text.
0.0050
CdVO3
T = 2 K
0.0025
Cd0.8Na0.2VO3
0.0000
-0.0025
-0.0050
-80
-60
-40
-20
0
20
40
60
80
Magnetic Field (kOe)
Fig. 6. The isothermal magnetization curves, M versus H, at T ¼ 2 K for CdVO3 (circles) and Cd0.8Na0.2VO3 (squares).
the S ¼ 1=2 local moment in CdVO3 and Cd0.8Na0.2VO3,
respectively. The a values of CdVO3 and Cd0.8Na0.2VO3 were
very small and close to those of single crystals of CaVO3 and
SrVO3 [5], suggesting that the deviation from a temperature-
independent Pauli paramagnetism is also very small.
The isothermal magnetization curves of CdVO3 and
Cd0.8Na0.2VO3 at 2 K showed no hysteresis and reached
only about 0.004 mB/mol at 7 T (Fig. 6). Almost the same
value of magnetization was observed at 5 K and 5 T in
CaVO3 (0.003 mB/mol [13]) and SrVO3 (0.002 mB/mol [5]).
This fact indicates that only paramagnetic moments
contribute to the total magnetization.
could be fit by the equation
Cp ¼ gT þ b1T3 þ b2T5,
(4)
where the first term is ascribed to the electronic contribu-
tion with g ¼ 13p2kB2 Nð0Þ (where N(0) is the electronic
density of states at the Fermi level and kB is Boltzmann’s
constant), and the second and third terms describe the
lattice contribution. The specific heat and magnetic
susceptibility data showed no evidence for a magnetic
phase transition in CdVO3 and Cd0.8Na0.2VO3. The g
values were 13.4(1) mJ/(mol K2) in CdVO3 and 11.2(1) mJ/
(mol K2) in Cd0.8Na0.2VO3. These values are close to those
of single crystals of CaVO3 (9.25 mJ/(mol K2)) and SrVO3
(8.18 mJ/(mol K2)) with strongly correlated electrons [5].
For example, in the less correlated sodium metal,
g ꢁ 1 mJ=ðmol K2). The values of b1 gave the Debye
We also observed the electronic contribution to
the specific heat at low temperatures in CdVO3 and
Cd0.8Na0.2VO3 as can be seen from the Cp/T versus T2
plots (Fig. 7b). The specific heat between 1.8 and 10 K

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0.5
0.4
0.3
0.2
0.1
0.0
Anomaly due to the
sample puck
0
20
40
60
80
100
(a)
Temperature (K)
0.03
0.02
0.01
0.00
Cp = ꢃT + ꢄ T3 + ꢄ2T5
CdVO3
ꢃ= 0.0134(1) J K-2mol-1
ꢄ1 = 7.5(7)x10-5 J K mol-1
ꢄ2 = 2.9(8)x10-7 J K-6 mol-1
1
-4
Cd0.8Na0.2VO3
ꢃ= 0.0112(1) J K-2mol-1
ꢄ1 = 5.6(7)x10-5 J K-4 mol-1
ꢄ2 = 3.7(8)x10-7 J K-6 mol-1
0
20
40
60
80
100
2
2
(b)
T
(K )
Fig. 7. (a) Total specific heat divided by temperature, Cp/T, plotted against T for CdVO3 (circles) and Cd0.8Na0.2VO3 (squares). (b) The Cp/T versus T2
curves for CdVO3 and Cd0.8Na0.2VO3 (symbols). The solid lines are the fits to Eq. (4) with the parameters given on the figure.
1=3
temperature, YD ¼ ð234 NkB=b1Þ
(N is Avogadro’s
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