6
806 Inorganic Chemistry, Vol. 48, No. 14, 2009
Kuti et al.
21
˚
n= 2 member of the AP phase, Bi W O (c= 23.7063(5) A).
The fundamental difference between the RP Sr Ti O and AP
and was left to fully dry at ambient room temperature on a
watch glass overnight.
2
2 9
3
2 7
structure Bi W O is that the Sr occupies the A-site cubocta-
Phase, Microstructure, Thermal, and Electrical Char-
acterization. The powder sample was characterized by PXRD
using a Bruker D8 powder X-ray diffractometer (Cu KR, 40 kV,
40 mA) at room temperature with a 2θ step scan width of
0.02°. The lattice constant was determined from the PXRD data
by least-squares refinements. Scanning electron microscopy
2
2 9
22
hedra site and falls between the perovskite-like layers in the
2
-
RP phase, while in the AP phase, the {Bi O } separates the
2
2
23
A-site-deficient perovskite-like layer.
24-27
In our continuing pursuit
of the development of solid
oxide ion electrolytes for intermediate-temperature solid
oxide fuel cells, we intended to prepare oxide ion-conducting
(
SEM; Philips XL30 SEM) coupled with an energy-dispersive
X-ray analysis (EDX) and transmission electron microscopy
(TEM; Hitachi H700, TEM, Japan) were used for chemical
composition and microstructure characterization.
doped SrWO by using a precipitation reaction. In our first
4
experiment, we dissolved SrCO in dilute HCl instead of
3
aqueous SrCl . Astonishingly, we observed a greenish yellow
Thermogravimetric analysis (TGA) was performed for
as-precipitated materials in the temperature range 25-800 °C
using a Netzsch 449C Simultaneous Thermal Analyzer in the air
(5 °C/min). Further characterization involves Fourier transform
infrared spectroscopy (FTIR) using a NEXUS 470 FT-IR
spectrometer. The powder sample was dispersed in KBr pellets
for measurements. Before FTIR measurements, the KBr pow-
der was dried continuously at about 100 °C in a vacuum oven.
The alternating current (AC) electrical conductivity (Solartron
SI 1260; 100 mV; 0.01 Hz to 7 MHz) was measured using
2
precipitate instead of the expected white-color SrWO4.
A PXRD study showed the formation of a layered structure,
28
rather than the regular tetragonal scheelite-type structure.
Hitherto, A-site-deficient DOLS tungsten trioxide hydrates
20,21
(TTHs) were prepared generally by acid leaching;
here,
we report a simple precipitation reaction method to synthe-
2
size RP-related structure DOLS-TTH involving Na WO4
and SrCl + 3 M HCl. This paper describes the preparation,
2
dehydration properties, intercalation reaction, microstruc-
ture, and particle size characterizations as well as the elec-
trical (proton) conductivity of the new metastable TTHs.
Pt-C electrodes in wet N (water kept at room temperature)
2
for five days. A two-probe electrochemical cell was employed for
electrical characterization.
Results and Discussion
Experimental Section
Synthesis and PXRD Characterization. Figure 2 shows
the PXRD patterns of three different crystal structure
products obtained by precipitation from aqueous Na WO
2 4
Preparation of A-Site-Deficient Layered Perovskite-Type
WO 1.3H O (ꢀ 1/2H W O 1.6H O). The desired amount
3
of high-purity SrCl
3
2
2
(99.7%, Fisher Scientific) was dissolved in a
2
7
3
2
2
minimum quantity of 3 M HCl (Hydrochloric acid GR, ACS;
EMD Chemical Inc.) and the result called solution A. In another
and SrCl (dissolved in 3 M HCl, 9 M HCl, and water).
2
Using 3 M HCl, we clearly see the formation of a new layered
beaker, appropriate amounts of high-purity Na
(99%, Alfa Aesar) were dissolved in a minimum amount of
2 4 2
WO 2H O
3
structure (Figure 2a) that is similar to that of H W O 0.58
2 2 7
3
˚
20,21
H O.
2
The first peak with d spacing of about 12.5 A is
deionized water, until a colorless solution was formed (solution
B; pH = 10.3). The pH of the solutions was determined using a
pH meter (Accument pH Meter 910; Fisher Scientific). Upon
complete dissolution, the two solutions were poured together into
a third, clean, large glass beaker, and a light green precipitate was
formed instantly. The resultant solution had a pH close to 1. The
precipitate was washed thoroughly with deionized water multiple
times using a decanting method, after which the precipitate was
vacuum-filtered and dried at ambient room temperature on a
watch glass overnight. The precipitate was then scraped off the
watch glass and placed in a ball mill (Pulverisette, Fritsch,
Germany) for about 15 min at 200 rpm using zirconia balls to ensure
efficient grinding of the solid precipitate into a powderlike form.
Preparation of Layered Structure WO 2H O. In beaker
consistent with a double-perovskite slab containing layered
21
structure compounds, including Bi W O , CaEu Ti O
2 8
2
2
9
2
29
22
˚
13.56 A), and Sr Ti O , which corroborates with the
3 2 7
(
layered DOLS TTHs. However, the present synthesis
showed a very broad peak, suggesting a poor crystallinity.
This unexpected result was repeated several times, and our
results continually showed a similar XRD pattern. Also, it is
very important to mention that the n = 1 member of the RP
phase ALnTiO (A = Na, K; Ln = La or rare earth) shows
4
30
a very similar interlayer spacing. The large unit cell in the
ALnTiO structure is due to alternative ordering of alkali
4
and rare earth ions around the corner-sharing single sheet of
TiO octahedra. The n = 2 members of the Dion-Jacobson
3
3
2
6
A, appropriate amounts of high-purity SrCl
2
(99.7%, Fisher
0
31
] (A = alkali metal; A = alkaline
0
phases A [A B O
n-1 n 3n+1
Scientific) were dissolved using 9 M HCl (hydrochloric acid GR,
ACS; EMD Chemical Inc.) in a clean beaker (A). In a second
earth, rare earth; B = Nb, Ta, Ti) exhibit, generally, slightly
lower layer spacing compared to those of the corresponding
(n = 2 member) RP phase.
beaker B, appropriate amounts of high-purity Na
(
2 4 2
WO 2H O
3
32
99%, Alfa Aesar) were dissolved in deionized water, until
forming a colorless solution with a pH of 10.3. Upon complete
dissolution of both compounds in beakers A and B, the two
solutions were poured together into a large glass beaker, upon
which a bright yellow precipitate was formed. The precipitate
was washed thoroughly with water using a decanting method
multiple times, after which the precipitate was vacuum-filtered
(
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