Effect of MWO4 (M = Ca, Sr, Ba) dispersion on the interfacial processes in (+/-)WO3|MWO4|WO3(-/+) cells and transport properties of metacomposite phases

Article abstract of DOI:10.1134/S0036023610060082

We compare data on the reciprocal electrosurface transfer (EST) of WO ₃ and MWO₄ components through WO₃|MWO ₄ eutectic heterointerfaces using MWO4 (M = Ca, Sr, Ba) samples prepared by standard ceramic technology (CER) and nitrate-organic technology (N/O); these samples considerably differ in both the grain size of precursor powders and the grain size of sintered ceramics. When an electric field is applied, the interpenetration of WO₃ and MWO₄ components occurs though WO₃|MWO₄ (M = Ca, Sr, Ba) heterointerfaces. The general^(-)WO₃ MWO₄⁽⁺⁾ intermigration pattern in the cells is not influenced by tungstate preparation technology. However, interpenetration rates are far greater forMWO ₄^N/O. The transport properties of {MWO₄ ·_xWO₃} two-phase eutectic metacomposites manufactured by both technologies were studied. Tungstate and composite manufacturing technologies have no radical influence on the electric properties (overall and partial conductivity, transference numbers) of the samples, only changing conductivity versus concentration relationships. Our data well fit the model of formation of a nonautonomous electrolytic inter-phase. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036023610060082

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 6, pp. 876–882. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © N.N. Pestereva, I.G. Safonova, S.S. Nokhrin, A.Ya. Neiman, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 6, pp. 940–946.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Effect of MWO4 (M = Ca, Sr, Ba) Dispersion on the Interfacial
Processes in (+/–)WO3|MWO4|WO3(–/+) Cells and Transport
Properties of Metacomposite Phases
N. N. Pestereva, I. G. Safonova, S. S. Nokhrin, and A. Ya. Neiman
Ural State University, Yekaterinburg, Russia
eꢀmail: Arkady.neiman@usu.ru
Received February 12, 2009
Abstract—We compare data on the reciprocal electrosurface transfer (EST) of WO3 and MWO4 components
through WO3|MWO4 eutectic heterointerfaces using MWO4 (M = Ca, Sr, Ba) samples prepared by standard
ceramic technology (CER) and nitrateꢀorganic technology (N/O); these samples considerably differ in both
the grain size of precursor powders and the grain size of sintered ceramics. When an electric field is applied,
the interpenetration of WO3 and MWO4 components occurs though WO3|MWO4 (M = Ca, Sr, Ba) heterointꢀ
(+)
erfaces. The general (–)WO3
MWO4 intermigration pattern in the cells is not influenced by tungstate
preparation technology. However, interpenetration rates are far greater for MWON4 /O . The transport properꢀ
ties of {MWO4 · WO3} twoꢀphase eutectic metacomposites manufactured by both technologies were studied.
x
Tungstate and composite manufacturing technologies have no radical influence on the electric properties
(overall and partial conductivity, transference numbers) of the samples, only changing conductivity versus
concentration relationships. Our data well fit the model of formation of a nonautonomous electrolytic interꢀ
phase.
DOI: 10.1134/S0036023610060082
MWO
Processes occurring at homoꢀ and heterointerfaces using
samples prepared by standard ceramic
4
technology. The following qualitative trends were
observed in those works:
considerably influence the reactivity, thermodynamic,
and kinetic stability of singleꢀphase and composite
nanostructured objects. The least studied and the most
mysterious are electricꢀfieldꢀstimulated processes [1–
3]. Solidꢀphase electrosurface phenomena include
solidꢀphase electrocapillarity, fieldꢀinduced electroꢀ
surface transport of oxides, electroosmotic migration,
and a flow potential [1–3]. Fieldꢀstimulated reactionꢀ
Q
МWO4
(1) As the amount of charge passage
WO3
(C)
increased, the
weight transferred to
МWO
WO
ceramics increased, too (the
weight), and accordingly, the
brick gained in
3 cathodic brick lost
4
WO
in weight;
as an autonomous phase filledꢀin a
3
МWO
portion of the inner surface of
greenish color front of the
ceramics. The
4
WO
CaWO
less pullingꢀin of
to the inner surface of
3
4
МWO
4 brick (the boundary
ceramic bricks was first described in [4, 5]. A very
important discovery was the twoꢀway character of both
spontaneous and fieldꢀstimulated processes [1, 6];
WO3
of
МWO
penetration across the inner surface of the
4 brick) propagated toward the (+) electrode; as
(–)
МWO
хWO
W
brick adjacent to O3 ,
a result, part of the
MWO ·
converted to an {
WO
MWO
3 is pulled to the inner surface of
4 ceramics,
4
MWO
and in turn,
4 components propagate (but in far
3} composite.
4
WO
smaller amounts) across the surface of
3, irreversꢀ
(+)
W
(2) The O3 anodic brick had its weight virtually
ibly changing their color. Further, this process was
(+)
WO |MWO
found to be intrinsic to all
Ba) interfaces [7].
(M = Ca, Sr,
3
4
W
unchanged; after the experiment was over, the O3
section was always lightened uniformly, but recovered
its natural color as soon as after 1ꢀh annealing in air at
In earlier works [1, 4–7], experiments on spontaꢀ
neous and electrosurface transport through the
800
(3) The O3 section changed its color to dark
МWO
°
С
.
(–)
WO3|МWO
cells
4 interface were carried out in symmetrical
W
green. Coloring started in the nearꢀ
4 region, and
as the current passed, the darkening zone gradually
(–) Pt⏐WO3
⏐
MWO4
(М = Са, Sr, Ba)
⏐
WO3⏐Pt (+)
(–)
W
Pt(–)
propagated across O3 in the direction of the
(1)
876

EFFECT OF MWO4 (M = Ca, Sr, Ba) DISPERSION
877
electrode and colored the entire thickness of the calcined at 400–600°С before use. Tungsten oxide
(–)
WO3 in (NH4)10W12O41 was determined gravimetrically
by calcining to constant weight at 500°С. The WO3
percentage was 88.78 wt %.
W
1000 С
O3 brick. Additional annealing in air for 5 h at
°
did not change the darkꢀgreen color of the
(–)
W
O3 section.
The nitrateꢀorganic synthesis of МWO4 and its
composites is illustrated by the scheme below.
The interpretation of the aboveꢀdescribed pheꢀ
nomenon was based on the solidꢀphase electrocapilꢀ
larity model [1, 4, 5]. But the key role in electrosurface
transfer (EST) is played by the deep transformation of
the WO3|MWO4 heterointerface, namely, by the formaꢀ
) M2+, NO3–,
H2O
(b) (NH4)10W12O41 + C4H6O6(exc.) + H2O
(a
tion of a nonautonomous МWꢀ
electrolytic conductivity ((tO2–
bilateral surface activity (2) and mobility (3) [1, 6, 7]:
s
≈
interphase, which has
1) and, importantly,
Working solution (с)
–
M
2+, [WO2(C4H2O6)]2–, NO3, H2O, C4H6O6
(2)
α
< α
< α
,
MWO4
MWꢀs
WO3
Concentrating
(3)
DMWꢀs→WO ≈ DMWꢀs→MWO
.
4
3
Intermediate product
Calcining
Most complete data in support of МWꢀ
s
formation
and the bilateral transfer of its components were
gained by ESCA, highꢀtemperature powder Xꢀray difꢀ
fraction, and Xꢀray fluorescence analysis [7, 8].
Perhaps, the most unexpected result was the fieldꢀ
700°С–2
800°С–6
900°С–6
h
h
h
stimulated pullingꢀin of the МWꢀs electrolytic interꢀ
phase to the inner surface of the electronꢀconducting
WO3 and its grainꢀboundary migration in the “–”
{МWO4 ⋅ xWO3}
direction. Noteworthy is the recent substantiation of a
hypothesis that the irreversible darkening of the
We calculated weights of alkalineꢀearth carbonates
and ammonium paratungstate (NH4)10W12O41
(–)
W
O3 brick arises from the appearance of a dense film
required to prepare MWO4 and {МWO4
0–0.3) composites.
⋅
xWO3} (x =
of an M–W tetragonal bronze phase on grain surfaces
(–)
of the
WO3 brick [9].
To prepare solution (a) МCO3 was placed in a vessel
containing 25 mL water followed by slow addition of
then dilute HNO3. Vigorous carbon dioxide gas evoluꢀ
tion was observed.
(NH4)10W12O41, together with a twofold weight
excess of tartaric acid С4H6O6, was dissolved in
125 mL water under moderate heating. Yellowish
The aboveꢀdescribed data were obtained in experiꢀ
ments on micronꢀsized МWO4 ceramics prepared by
ceramic technology. However, inasmuch as spontaneꢀ
ous and fieldꢀstimulated migrations of oxides are
developed on the inner surfaces of ceramic bricks, it is
reasonable to suggest that the process rates would
depend on the degree of surface development, that is,
on the MWO4 grain size.
solution (
poured to warm (40–50
The resulting solution was working solution (
contained all necessary components. Solution (
b
) was obtained. Solution (
) solution ( ) under stirring.
), which
) was
a) was slowly
°С
b
WO
MWO
Here we gain data on the EST of
to
c
4
ceramics with far smaller grain sizes pr3epared by
nitrateꢀorganic technology. EST rates, conductivities,
and transference numbers are compared between
c
transferred to a ceramic cup and concentrated to dryꢀ
ness to obtain a yellow waxy intermediate product,
which then rapidly crystallized at room temperature.
The intermediate product was calcined with temperaꢀ
MWO
4 ceramics and {
MWO ·
хWO
3} composites preꢀ
4
pared by the aforementioned nitrateꢀorganic and
ceramic technologies.
ture elevated in steps from 700 to 900°С and intermitꢀ
tent grinding in an agate mortar.
The МWON4 /O (M = Ca, Sr, Ba) powders were synꢀ
EXPERIMENTAL
Synthesis. The ceramic procedure for manufacturꢀ thesized with grain sizes of 80–100 nm (Shimadzu
ing MWO4 ceramics and {(1 – )MWO4 · WO3} (hereꢀ
after, {MWO4 · WO3}) composites is descried in [4, 5].
SALD 7101 grain size analyzer). МWOC4 ER (M = Ca,
Sr, Ba) powders had grain sizes of 3–7 m (SEM).
Reactive WO3 grains had sizes of 2–5 m (SEM).
МWO4 and composite blends were compacted on a
Са, Sr, Ba), tartaric acid С4H6O6 (pure for analysis handꢀoperated hydraulic press in a steel mold (pcomp
grade), and aqueous (1 : 3) nitric acid HNO3 (high 640 kg/cm2). Bricks (2–5
10) were sintered for 6 h at
purity grade 8ꢀ4). The MCO3 precursor samples were 930 and then polished to obtain planeꢀparallel surꢀ
х
х
х
μ
The precursors for nitrateꢀorganic technology were
ammonium paratungstate (NH4)10W12O41 (pure for
analysis grade), МCO3 (high purity grade 16ꢀ2), (
μ
М =
=
×
°С
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

878
PESTEREVA et al.
, h
m(SrWO4), g
τ
τ, h
Δ
m(CaWO4), g
Δ
5
10 15 20 25 30 35 40
5 10 15 20 25 30 35 40
0.04
0.03
0.02
0.01
0.04
0.03
0.02
0.01
N/O
CER
N/O
CER
0
20 40 60 80 100120 140 160
, C
0
20 40 60 80 100120140160
Q, C
Q
Fig. 1. WO weight transferred to MWO ceramics vs. electricity amount;
T
= 900°C,
I
= const = 1 mA.
3
4
tO2–
tO2–
1.0
1.0
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
x
x
x
x
x
= 0
x
x
x
x
x
= 0
BaWO4 ·
x
WO3
= 0.05
= 0.15
= 0.25
= 0.30
= 0.05
= 0.15
= 0.25
= 0.30
SrWO4 ·
xWO3
600
700
800
900
600
700
800
900
T, °C
Fig. 2. Transference number vs. temperature for {SrWO · хWO } and {BaWO · хWO } composites (prepared by N/O technology.
3 4 3
4
faces. The relative densities of the samples were 0.75–
0.80.
Transference numbers tO2– were determined by the
emf method in the cell
Electron microscopic investigations were carried
out using Hitachi Sꢀ4100 and JCXAꢀ733 electron
microscopes.
'
''
WO3}|(Pt) aO
aO
(Pt)|{МWO4 ·
х
(4)
2 = 0.21
2 = 1
The details of the procedure are found in [10].
Particle sizes of MWON4 /O sintered ceramics were
Conductivity measurements were carried out on an
IPUꢀ1 virtual impedometer in the frequency range
m; those of MWOC4 ER sintered ceramics
m.
50–105
1.0–1.5
μ
Hz. Some measurements were performed at
were ≈ 5–10
μ
1 kHz.
Experimental fieldꢀstimulated migration data were
obtained with the use of electrochemical cell (1) at
900 C. Platinum electrodes were shaped as platelets.
The assembly was placed into a furnace preheated to
the required temperature. The isothermal exposure
temperature was reached within 10 min. Then, the
potential was applied to the system from a B5ꢀ49
RESULTS AND DISCUSSION
°
Electrosurface Transfer
This work mostly concerns М2+ = Sr or Ba, because
previous works [1, 4, 6, 7, 10] mainly concerned elecꢀ
CaWO
4. The electrosurface
trosurface transfer in
source. The current was maintained at
I ≈ 1 mA. Variꢀ
transfer experiments here were carried out in a galꢀ
vanostatic mode, where the current had a fixed value
of 1 mA. Charges of up to 90 C were passed through
ous amounts of electricity were passed through the
cells.
The course of the process was monitored by weighꢀ the cells. The process rate was judged from the gain in
МWO4
=
ing the contacting bricks before and after annealing on
a Sartorius analytical balance with an error of 0.0001 g. VEST
brick weight per unit time for a fixed current:
(Δ
m/ )
I = 1
mA
τ
.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

EFFECT OF MWO4 (M = Ca, Sr, Ba) DISPERSION
879
{SrWON4 /O
·
xWO3}
{SrWOC4 ER
·
x
WO3}
tO2–
1.0
0.8
0.6
tO2–
1.0
880
°
C
800
700
600
°C
°C
°
C
0.8
0.6
0.4
0.2
0
900
800
700
°
°
C
C
C
0.4
0.2
°
0
0.1
0.2
{BaWON4 /O
0.3
·
0
0.1 0.2 0.3 0.4 0.5 0.6
{BaWOC4 ER
WO3}
x
WO3}
· x
tO2–
tO2–
1.0
0.8
0.6
0.4
0.2
1.0
870
°
C
800
700
650
°
°
°
C
C
C
0.8
0.6
0.4
0.2
0
860
800
700
°
C
°
C
C
°
0
0.1
0.2
WO3
0.3
0
0.1
0.2
0.3
xWO3
0.4
0.5
0.6
x
SrWO ·
Fig. 3. Transference number vs. concentration for {
хWO
BaWO ·
хWO
} composites prepared by various methods.
3
} and {
3
4
4
The curves plotted in Fig. 1 present the tungsten
МWO4
curves definitely show that the electrosurface migraꢀ
tion of tungsten oxide to the ceramics prepared by
nitrateꢀorganic technology occurs at far higher rates
than in ceramic samples:
МWꢀs
nonꢀ
always coated (“poisoned”) by a film of an
oxide weight transferred to
ceramics. These
autonomous phase, whatever it has a minimal thickꢀ
WO
3 pullꢀ
ness [1, 2–8], which evidently reduces the
ingꢀin rate.
The foregoing is verified by the EST current effiꢀ
χ
WO
ciency ratio ( ), a value showing the number of
gꢀequivalents transported by the 1 F charge [4, 5],
3
V
EST(WO3
CaWON4 /O)/VEST(WO3
CaWOC4 ER) ≈ 2.0
(5)
ΔmWO
F
Q
3
χ = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
“zWO
”
ꢀꢀ
,
(7)
and
3
MWO
3
V
EST(WO3
SrWON4 /O)/VEST(WO3
SrWOC4 ER) ≈ 2.7.
(6)
where
the molar weight of a WO3 mole, “
of WO3 gꢀequivalents per mole
charge passed through the system (coulombs).
Δ
mWO is the transported WO3 weight, MWO is
3
3
z
WO ” is the number
3
The different EST rates most likely arise both from
the smaller grain size of N/O ceramics (i.e., the greater
inner surface accessible to accommodate
(z
= 6), and
Q
is the
WO
3) and
from the specifics of N/O technology, where grain surꢀ
N/O
CaWO4
CER
CaWO4
WO
faces are washed from the
3ꢀcontaining impurity
χ
= 0.97;
= 0.99;
χ
χ
= 0.45
= 0.41
⎫
⎬
⎭
phase (see scheme). Finally, the purer and fresher surꢀ
(8)
N/O
SrWO4
CER
SrWO4
N/O
χ
MW
faces of
O4
ceramics are more susceptible
WO
(more adhesionꢀactive) to coverage with a
flow.
3
For MWON4 /O
even though being nominally stoichiometric, are value = 1.
,
χMWO values are close to the limiting
4
N/O
CER
MW
However, it is well known that
O4
ceramics,
χ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

880
PESTEREVA et al.
[ ]
–1cm–1
ω
log
–1
σ
[ω
–1cm–1
]
log
–1
σ
–2
–3
–4
–5
–2
–3
–4
–5
–6
–7
700
°
С
870
{SrWO · x
WO }CER
4
°
С
{SrWO ·
4
x
WO }N/O
3
3
–6
–7
0
0.2
0.4
0.6
0.8
1.0
0
0.2
0.4
0.6
0.8
1.0
–1
–2
–3
–4
–5
–6
–7
–1
–2
–3
–4
–5
–6
–7
700
°
С
870
°
С
{BaWO ·
4
x
WO }N/O
{BaWO ·
4
x
WO }CER
3
3
0
0.2
0.4
0.6
WO
3
0.8
1.0
0
0.2
0.4
0.6
xWO
3
0.8
1.0
x
SrWO ·
Fig. 4. Ion conductivity vs. concentration for {
хWO
BaWO · хWO
} and { } composites prepared by various methods.
4 3
4
3
Transference Numbers and Conductivity
Figure 2 shows ion transference numbers as a funcꢀ
tion of temperature in {МWO4 · WO3} (M = Sr, Ba)
composites. We refer the experimentally determined
transference numbers to the oxygen conductivity conꢀ
whereas for ceramically synthesized samples it was
slightly greater and reached = 0.20 (Fig. 3).
х
The {МWON4 /O
WO3} (M = Sr, Ва) composites
synthesized and characterized in this work, as well as
·
х
х
(CER)
tribution because earlier works [11, 12] substantiated previously studied {СаWO4
· хWO3}, are classified
that oxygen is the majority ion charge carrier in
scheeliteꢀrelated compounds and materials.
as metacomposites [10], because the properties of a
composite as a whole are not intrinsic to any of its conꢀ
stituent.
Resuming, we find that the preparation technology
and grain size are most decisive for the electrosurface
transfer rate, while the transport properties of mulꢀ
tiphase MeWO4 and their composites are far less sensiꢀ
tive to the preparation technology and grain size.
Analyzing the data obtained for the {МWO4 ·
(M = Sr, Ва) composites (Fig. 2), we infer the following:
(i) For most (N/O) composites having 0 < < 1
хWO3}
tO2−
either increases with rising
(mixed conductors),
tO2−
temperature or remains unchanged, whereas for
(CER)
МWO4
{
· хWO3} (M = Sr, Ва), the respective value
Pertinently, the aforementioned trends are related
always drops in response to rising temperature. This
trend might signify the different transport properties of
МWO4|WO3 interfaces in composites prepared by difꢀ
ferent technologies. Recall that a similar behavior of
to the fact that, during EST in cells with MWON4 /O , the
incorporation of WO3 and its propagation occur at
MWO4 grain surfaces, which are nominally “pure”
(see above) and free of impurity phases.
(
Т
)
has been earlier described and analyzed for
tO2−
(CER)
On the contrary, the WO3|MWO4 interface appears
coated with a surfaceꢀactive and kinetically active
{СаWO4
· хWO3} composites [5], which were also
manufactured by ceramic synthesis.
(ii) The electrolytic region for the composites preꢀ
pared by nitrateꢀorganic technology was
phase WO3ꢀ
s
as early as at the sintering stage. This
(N/O)
induces recrystallization of MWO4
matrix grains
х
≤
0.15,
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

EFFECT OF MWO4 (M = Ca, Sr, Ba) DISPERSION
881
1
μ
m
1 μm
CaWO4 brick
WO3 brick
Incident energy: 25.0 keV
Measure time: 169 s
Pulse rate: 1175 cps
Incident energy: 25.0 keV
Measure time: 164 s
Pulse rate: 1447 cps
W
4
3
2
1
3
2
1
Ca
CO
O
Ca
W
W
C
W
0
2
4
6
8
eV
0
2
4
6
8
10 12 14 keV
N/O(+)
(–)
3
WO
CaW
O4
Fig. 5. SEM images and EDA analysis of cleaves from contact surfaces of
and
bricks after annealing in cell (1).
and changes the transport properties of the inner surꢀ in film thickness of the WO3ꢀs phase, which is maniꢀ
face of N/O ceramics. As a result, the conductivities
and transference numbers of N/O and CER samples
converge.
fested as the monotonic rise in σion
.
Further, the aforementioned increase in
in
tO2−
response to temperature elevation for most (N/O)
composites having 0 < < 1 (mixed conductors),
However, there are substantial distinctions, in parꢀ
tO2−
ticular, in the initial segments of the σion
0 < 0.2 (Fig. 4). For N/O samples, we observe a
nearly monotonic rise in σion, while for CER samples
characteristic is a local plateau starting at small . This
behavior is explained by different grain sizes and sp of
(х) plots where
indicates a considerable dependence of the ion transꢀ
port parameters on the technology and morphology of
the ceramics. The nature of this dependence is to be
understood, which will be done elsewhere.
Recall that the key role in EST is played by the
MWꢀs nonautonomous interphase, which exists only
х
≤
х
S
composites manufactured by different technologies.
MWOC4 ER samples have large grains and relatively
small inner surface areas. In this case, a small WO3
amount is sufficient for forming a through film of an
within a limited range of high temperatures [1, 5, 13].
Another piece of evidence in favor of the existence of
this phase is provided by the SEM inspection of the
products of its decomposition in interface regions carꢀ
ried out after the contact annealing of the
ionꢀconductive WO3ꢀs interphase with the thickness
providing a maximal total ionic conductivity (the plot
enters a local plateau). For MWON4 /O samples (having
CaWOC4 ER |WO3 couple [7, 13].
Here, we carried out similar SEM–EDA studies but
smaller grain sizes and greater inner surfaces), increasꢀ
ing х
leads to a systematic increase in connectivity and for nearꢀcontact regions of the (+)CaWON4 /O |WO3(–
)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

882
PESTEREVA et al.
s
phase in the vicinity of the МWON4 /O |WO3
couple. The exfoliation and peeling of a WO3ꢀbased
film (as probed by EDA) is well seen in the SEM image
of the surface of a CaWON4 /O brick across which the WO3
MWꢀ
interface.
(–)
phase propagated from the
WO3 electrode (Fig. 5). In
ACKNOWLEDGMENTS
turn, calciumꢀcontaining precipitates of tubular
This work was supported by grants of the Ministry of
Education and Science of the Russian Federation and
by the Russian Foundation for Basic Research (project
nos. 08ꢀ03ꢀ00144ꢀa and 04ꢀ03ꢀ32614ꢀa). The authors
are grateful to E.V. Tsipis for performing grainꢀsize
analysis and A.A. Pankratov for SEM studies.
(–)
shapes are observed on a chip of a
WO3 brick after
contact with CaWO4 (as probed by EDA). Both film
and tubular precipitates are the degradation products
of the MWꢀs nonautonomous phase, which is stable
only within a limited range of high temperatures (see
above). The aforementioned pattern is a complete
analogue of what was observed for the CaWOC4 ER |WO3
couple [7, 13]. This shows that the nature of interfacial
processes is not affected by the preparation technology
and morphology of МWO4 ceramics.
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To summarize, in
(
⎯
) Pt
|
WO3|MWO4|WO3 Pt (+)
|
(M = Са, Sr, Ba) cells we studied reciprocal electroꢀ
surface transfer of WO3 and MWO4 components
through WO3|MWO4 eutectic heterointerfaces. MWO4
ceramics were manufactured using ceramic technoꢀ
logy (CER) and nitrateꢀorganic technology (N/O).
МWON4 /O grain sizes are one order of magnitude
smaller than МWOC4 ER grain sizes. Qualitatively,
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(+)
⎯)WO3
MeWO4 intermigration has a similar
(
pattern. For MWON4 /O however, the electrosurface
transfer rates are two to three times as high. We have
shown that technology used to manufacture tungstates
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and {MWO4 · хWO3} twoꢀphase metacomposites only
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insignificantly influences the ion conductivity versus
concentration dependences and the electrolytic range.
The trends we discovered go in line with the model of
the formation of an electrolytic nonautonomous interꢀ
phase and its key role in the genesis of electrosurface
transfer. SEM–EDA supplied us with evidence for the
formation and intermigration of a nonautonomous
Solid State Ionics 177, 3361 (2007).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010