Synthesis and electrical properties of variable-composition phases Rb 1 - X A1 - X R1 + x (MoO4) 3 (0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)

Article abstract of DOI:10.1134/S1070427208100054

Subsolidus region of the ternary systems Rb₂MoO ₄-AMoO₄-R₂(MoO₄)₃, in which variable-composition phases Rb_{1 - x} A_{1 - x} R _{1 + x} (MoO₄)₃ crystallizing in the monoclinic system (space group C2) are formed, was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical conductivity, dielectric constant, and dielectric loss tangent were analized.

Full text of DOI:10.1134/S1070427208100054

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 10, pp. 1729–1732. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © N.M. Kozhevnikova, E.P. Ermakova, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 10, pp. 1601–1604.
INORGANIC SYNTHESIS AND INDUSTRIAL
INORGANIC CHEMISTRY
Synthesis and Electrical Properties of Variable-Composition
Phases Rb A R (MoO )
1
– x 1 – x 1 + x
4 3
(
0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)
N. M. Kozhevnikova and E. P. Ermakova
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, Ulan-Ude, Buryatiya, Russia
Received February 8, 2008
Abstract—Subsolidus region of the ternary systems Rb
2 4 4 2 4 3
MoO –AMoO –R (MoO ) , in which variable-com-
position phases Rb1 – x crystallizing in the monoclinic system (space group С2) are formed,
1 – x 4 3
A R1 + x(MoO )
was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical con-
ductivity, dielectric constant, and dielectric loss tangent were analized.
DOI: 10.1134/S1070427208100054
In the last two decades, an intensive search has
been in progress for functional materials with struc-
EXPERIMENTAL
p–
The starting components for studying the phase
formation in the systems Rb MoO –AMoO –R
tural skeletons {[R (ElО ) ] } , where R is an octahe-
2
4 3
∞
2
4
4
2
dral cation in phosphate, arsenate, molybdate, tung-
state, and sulfate systems [1–8]. Promising in this re-
gard are phases with langbeinite structure, Sc (WO )
(
MoO ) were Rb MoO , AMoO , and R (MoO ) ,
4 3 2 4 4 2 4 3
preliminarily synthesized by the solid-phase technique
from Rb СO , magnesium, nickel, cobalt, and manga-
nese oxides, molybdenum trioxide of analytically pure
grade, and scandium, ytterbium, and lutetium oxides
with a content of the main component not lower than
2
4 3
2
3
and K Mg (SO ) , which have bulk cavities partly
2
2
4 3
filled by singly charged cations. They exhibit high
conductivity by lithium, sodium, and silver ions [1].
As the radius of a cation increases, its mobility in tun-
nels and bulk cavities of the structure decreases, which
results in a lower conductivity of the phases [4].
9
9.99%. Oxides of divalent elements were preliminar-
o
ily calcined at 650 C for 8 h; Rb СO and MoO , at
2
3
3
o
o
4
00 C; and R O , in the temperature range 400–750 C.
The reaction mixtures of molybdates of rubidium and
di- and trivalent elements were calcined at 450–800 C
with multiple intermittent grindings every 20–30 h.
The time of calcination at each temperature was 120–
2 3
In a study of the systems K MoO –AMoO –
2
4
4
R (MoO ) (A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu),
o
2
4 3
variable-composition phases K1 – xA1 – xR1 + x(MoO4)3
0 ≤ x ≤ 0.5) belonging to the langbeinite structural
(
-3
–1
–1
type with a conductivity of 10 Ω cm were obtained
4].
1
50 h. After being annealed, the samples were slowly
[
cooled together with a furnace. Nonequilibrium sam-
ples were additionally annealed, with the equilibrium
considered to be attained if the phase composition of
samples remained constant after two successive an-
nealings. The synthesis products were identified by X-
ray phase analysis in an FR-552 chamber-mono-
chromator (CuKα radiation, internal standard Ge). The
X–ray diffraction patterns were processed using the
RENTGEN software. A differential thermal analysis
was performed on an MOM OD-103 derivatograph at a
The existence of structures with a considerable
volume of voids and the presence of centers unpopu-
lated by cations depend on the nature of the cations,
their combination, distribution over structural posi-
tions, and population of these positions. No data on
existence of the ionic conductivity in rubidium phases
are available, which is probably due to a decrease in
the mobility of a cation with its increasing radius.
The aim of this study was to synthesize variable-
.
–1
composition phases Rb1 – xA1 – xR1 + x(MoO ) and ex-
heating rate of 10 deg min and sample weight of 0.3–
4 3
amine their electrical properties.
0.4 g.
1
729

1
730
KOZHEVNIKOVA, ERMAKOVA
o
2 4 4 2 4 3 2 4 4 2 4 3
Fig. 1. Phase relationships in the systems (a) Rb MoO –MgMoO –Sc (MoO ) and (b) Rb MoO –MnMoO –Sc (MoO ) at 700 C.
Temperature dependences of conductivity σ, di-
deposited by firing-in a platinum paste. The electrical
properties were measured with an Е8-4 ac bridge with
a Р-5025 capacitor box at a frequency of 10 Hz
electric constant ε, and dielectric loss tangent tan δ
were studied by Vest and Tallan’s polarization tech-
nique [6] with densely compacted ceramic samples in
the form of pellets 10 mm in diameter and 1–1.5 mm
thick, with platinum electrodes. The electrodes were
3
(
measurement accuracy ±5%). The dc current was re-
corded with an Е6–13А teraohmmeter at a preset volt-
age of 30–50 mV.
Table 1. Crystallographic and thermal characteristics of Rb1 – x
A
1 – x
4 3
R1 + x(MoO )
Composition
a
b
c
o
B, deg
V/Z
mp, C
A
R
X
Å
Ni
Ni
Ni
Ni
Sc
Sc
Lu
Lu
0
0.2
0
16.246(2)
16.257(1)
16.262(2)
16.267(3)
9.371(3)
9.413(1)
9.405(3)
9.421(2)
9.922(1)
9.935(4)
9.941(1)
9.953(5)
122.95(1)
123.05(1)
123.16(1)
122.95(2)
316.7
318.5
317.9
319.5
1085
–
1068
0.2
–
Ni
Ni
Yb
Yb
Sc
0
0.2
0
0.2
0
0.2
0
0.2
0
0.2
0
0.2
0
02
0
16.267(2)
16.271(2)
16.254(3)
16.305(5)
16.248(4)
16.274(4)
16.276(5)
16.352(3)
16.314(5)
16.328(2)
16.402(1)
16.417(3)
16.415(1)
16.422(4)
16.337(5)
16.341(2)
16.358(4)
16.375(3)
16.381(4)
16.484(1)
9.411(1)
9.428(3)
9.386(2)
9.413(1)
9.344(3)
9.396(2)
9.398(1)
9.443(5)
9.435(3)
9.448(2)
9.452(3)
9.461(3)
9.465(3)
9.513(4)
9.598(1)
9.601(1)
9.645(1)
9.662(2)
9.665(4)
9.677(3)
9.969(4)
9.975(2)
9.929(2)
9.918(5)
9.948(3)
9.944(5)
9.875(2)
9.827(2)
9.968(4)
9.974(2)
9.979(2)
9.982(3)
9.987(1)
9.992(5)
10.023(2)
10.027(1)
10.019(4)
10.021(2)
10.081(4)
10.022(2)
123.08(1)
123.12(2)
122.98(2)
123.15(1)
122.99(2)
123.06(1)
122.72(1)
122.58(2)
123.06(1)
123.11(2)
123.13(1)
123.27(2)
123.19(1)
123.16(2)
122.70(9)
122.88(1)
123.16(1)
123.21(1)
123.37(2)
123.42(1)
319.7
320.2
317.7
318.6
317.8
318.9
319.1
320.5
321.4
322.4
324.1
324.2
324.7
326.7
330.0
331.4
331.9
332.9
333.1
333.7
1050
–
1070
–
1060
–
1040
-
1020
–
1005
-
993
-
970
–
Mg
Mg
Mg
Mg
Mg
Mg
Co
Co
Co
Co
Co
Sc
Lu
Lu
Yb
Yb
Sc
Sc
Lu
Lu
Yb
Yb
Sc
Co
Mn
Mn
Mn
Mn
Mn
Mn
Sc
02
0
02
0
Lu
Lu
Yb
Yb
960
–
945
–
0.2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 10 2008

1 – x 4 3
SYNTHESIS AND ELECTRICAL PROPERTIES OF VARIABLE-COMPOSITION PHASES Rb1 – xA R1 + x(MoO )
1
731
The interaction in the systems Rb MoO –AMoO –
2
4
4
R (MoO ) was examined in the subsolidus region in
2
4 3
o
the temperature range 450–800 C. The study was car-
ried out in two stages. In the first stage, an X–ray study
of the phase composition of the samples corresponding
to the intersection points of all cuts existing in the sys-
tems Rb MoO –AMoO –R (MoO ) enabled triangula-
2
4
4
2
4 3
tion of the systems. In the second stage, the quasi-
binary cuts revealed were studied. The formation of ter-
nary molybdates RbAR(MoO ) was observed in the cuts
4
3
RbR(MoO ) –AMoO and Rb A (MoO ) –R (MoO )
4
2
4
2
2
4 3
2
4 3
o
at 600–650 C (Fig. 1). The phases of variable compo-
sition Rb1 – xA1 – xR1 + x(MoO ) are formed in a plane
4 3
of the triangle Rb MoO –AMoO –R (MoO ) and
2
4
4
2
4 3
along the cut RbAR(MoO ) –R (MoO ) .
4
3
2
4 3
Samples with compositions corresponding to the quasi-
binary cuts were prepared with a step of 2.5–5 mol %,
and those intended for refining the composition of
the ternary molybdate RbAR(MoO ) being formed
4
3
and of the homogeneity region of the variable-com-
position phases Rb1 – xA1 – xR1 + x(MoO ) , with a step
4 3
of 1 mol %. The samples were annealed at 450, 550,
Fig. 2. Temperature dependence of the conductivity
o
6
00, 650, and 700 C, and those with nickel and cobalt
σ. (1) RbMgSc(MoO
4
)
3
, (2) Rb0.8Mg0.8Sc1.2(MoO
4
)
3
,
o
compositions, additionally at 750 and 800 C. Single-
phase samples of Rb – xA1 – xR1 + x(MoO ) were ob-
(
3) Rb0.8Co0.8Lu1.2(MoO
4
)
3
, (4) Rb0.8Mn0.8Yb1.2(MoO
4
).
1
4 3
o
tained at 700–800 C with annealing for 180–200 h.
The X–ray diffraction analysis of Rb1 – xA1 – xR1 + x
(
MoO ) samples demonstrated that they are isostruc-
The electrical properties of Rb1 – xA1 – xR1 + x(MoO )
were examined in the temperature range 200–600 C
4 3
4
3
o
tural to each other and to the monoclinic modification
of KMgIn(MoO ) (space group C2, Z = 4). The X–ray
(Figs. 2 and 3). The conductivity σ of rubidium phases
4
3
–
9
–3
–1
–1
diffraction patterns of Rb1 – xA1 – xR1 + x(MoO ) were
varies within the range 10 –10 Ω cm (Fig. 2).
They are characterized by mixed ionic-electronic con-
duction with predominance of the electronic compo-
4 3
indexed in the monoclinic system, using unit cell pa-
rameters of the KMgIn(MoO ) single crystal [4]. They
4
3
melt incongruently in the temperature range 945–
nent (t = 0.62–0.73) having an activation energy of
0.92–1.28 eV (Table 2).
e
o
1
085 C (Table 1).
Table 2. Conductivity σ of Rb1 – x
A
1 – x
R
1 + x(MoO
4
)
3
, electron transport numbers t
e
а
, and activation energy Е of conductivity
Composition
300°C
600°C
8
–1
–1
3
–1
–1
A
R
X
σ ·10 , Ω cm
t
e
σ ·10 , Ω cm
t
e
a
E , eV
Ni
Ni
Mg
Mg
Co
Sc
Sc
Sc
Yb
Sc
Sc
Lu
Lu
Yb
Yb
0.2
0.2
0
0.2
0
0.2
0
0.2
0
0.42
6.43
1.46
7.51
7.55
9.83
12.2
36.1
7.39
92.4
0.68
0.70
0.69
0.68
0.69
0.68
0.71
0.70
0.69
0.72
2.48
3.14
3.67
5.65
6.13
7.92
5.64
6.97
8.46
9.77
0.64
0.66
0.65
0.64
0.67
0.64
0.63
0.65
0.62
0.62
1.15
1.12
1.28
1.23
1.05
1.02
0.99
0.95
0.96
0.92
Co
Mn
Mn
Mn
Mn
0.2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 10 2008

1
732
KOZHEVNIKOVA, ERMAKOVA
CONCLUSIONS
1) Variable-composition phases Rb1 – xA1 – xR1 + x
MoO ) (0 ≤ x ≤0.2), A = Mg, Mn, Co, Ni; R = Sc,
(
·
(
4
3
Yb, Lu were prepared by the method of solid-phase
reactions from rubidium carbonate, magnesium, man-
ganese, cobalt, nickel, scandium, lutetium, and ytter-
bium oxides, molybdenum trioxide, and also from mo-
lybdates of rubidium and di- and trivalent elements.
(
2) The Rb1 – xA1 – xR1 + x(MoO ) samples are iso-
4 3
structural to each other and crystallize in the mono-
clinic crystal system (space group C2).
(
3) The Rb1 – xA1 – xR1 + x(MoO ) samples have a mix-
4 3
ed ionic-electronic conduction with predominance of
the electronic component.
REFERENCES
1
2
3
4
. Asabina, E.N., Pet’kov, V.I., Boguslavskii, M.V., et al.,
Zh. Neorg. Khim., 2006, vol. 32, no. 3, pp. 1252–1260.
. Lazoryak, B.I. and Efremov, V.A., Zh. Neorg. Khim.,
1
987, vol. 32, no. 3, pp. 652–666.
. Ivanov-Shits, A.K., Bykov, A.B., and Verin, I.Yu.,
Kristallografiya, 1996, vol. 41, no. 6, pp. 1060–1062.
. Kozhevnikova, N.M. and Mosokhoev, M.B., Troinye
molibdaty (Ternary Molybdates), Ulan-Ude: Buryat.
Gos. Univ., 2000.
Fig. 3. Temperature dependence of (2, 4) dielectric con-
stant ε and (1, 3) dielectric loss tangent for (1, 2) RbMgSc ·
MoO
(
4 3 4 3
) and (3, 4) Rb0.8Mg0.8Sc1.2(MoO ) .
5
. Kalinin, V.B., Stefanovich, S.Yu., and Nogai, A., Izv.
Akad. Nauk SSSR, Neorg. Mater., 1986, vol. 22, no. 1,
pp. 107–112.
The dielectric constant ε and the dielectric loss
tangent tan δ show an exponential dependence on tem-
perature (Fig. 3). The absence of extrema in the curves
for the dielectric constant and dielectric loss tangent
6
7
. Vest, R.V. and Tallan, N.H., J. Appl. Phys., 1965,
vol. 36, no. 2, pp. 547–552.
. Catti, M. and Stramare, S., Solid State Ionics, 2000,
vol. 136–137, pp. 489–493.
indicate that Rb1 – xA1 – xR1 + x(MoO ) exhibits no phase
4 3
transitions and ferroelectric properties.
8. Duhlev, R., Acta Crystallogr. C., 1994, vol. 50, pp. 1525–1528.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 10 2008