@conference{
author = "Dapčevć, Aleksandra and Dejan, Poleti and Rogan, Jelena and Radojković, Aleksandar",
year = "2013",
abstract = "The oxide ion conductors have widely been investigated because of their application in many
devices with high economical and ecological interests, such as solid oxide fuel cells (SOFC).
-Bi2O3
polymorph possesses the highest known O2–
ion conductivity, which is one to two
orders of magnitude higher than that of stabilized zirconia at corresponding temperatures [1].
At the moment, the application of this high-temperature polymorph as an electrolyte in SOFC
requires temperatures above 730 °C. However, the doping allows -Bi2O3
stabilization to room
temperature and opens the possibility for construction of SOFC that will operate at
intermediate temperatures (ca. 350 °C) [2].
As it is found that some lanthanides are suitable dopants [3], the possibility to stabilize O2–
ion
conductors related to the -Bi2O3
polymorph in the Bi2O3–Tm2O3
system was investigated. Two
starting mixtures with compositions (Bi1–xTmx
)2O3
(x = 0.04 and 0.20) were homogenized in an
agate mortar, heat treated at 750 °C for 3 h and then slowly furnace cooled. The samples were
characterized by XRPD, DTA and SEI techniques.
Based on XRPD, the single-phase tetragonal β-Bi2O3
was identified in the sample with x = 0.04.
Its unit cell parameters, a = 7.742(2) and c = 5.650(2) Å, well-correspond to those of undoped
β-Bi2O3
[4]. On the other hand, the cubic -Bi2O3
phase was obtained in the sample with
x = 0.20. Its unit cell parameter was greater than the value reported for Tm-doped -Bi2O3
sample with x = 0.25 [3] (5.5033(9) vs. 5.478 Å). Both values are smaller than reported for
undoped -Bi2O3
[4]. This means that the unit cell parameter of cubic -Bi2O3
decreases as
Tm-content increases and it is in accordance with Tm3+ and Bi3+ ionic radii [5].
For the sample with x = 0.04, cyclic DTA curves showed one reversible β-Bi2O3 ↔ -Bi2O3
transition with corresponding temperatures: on heating, 660 °C, and, on cooling, 600 °C.
Surprisingly, no phase transitions were observed in the sample with x = 0.20 which indicates
that the obtained -Bi2O3
is stable within the whole investigated interval, i.e., from room
temperature to 1000 °C.
Electrochemical impedance of -Bi2O3
phase was measured in the following temperature
range: 300 – 800 °C. At higher temperatures (600 – 800 °C) the conductivities are similar
(0.11 – 0.32 S cm
–1
), but with lowering temperature they rapidly decrease, and amount, for
example, 2.1·10–5
S cm–1
at 300 °C. As a consequence, two activation energies are found:
0.45(4) eV (600 – 800 °C), and 1.33(2) eV (300 – 600 °C).
References:
[1] P. Shuk, H.-D. Wiemhöfer, U. Guth, W. Göpel, M. Greenblatt, Solid State Ionics 89 (1996) 179
[2] E. D. Wachsman, K.T. Lee, Science 334 (2011) 935
[3] H. T. Cahen, T. G. M. Van Den Belt, J. H. W. De Wit, G. H. J. Broers, Solid State Ionics 1 (1980) 411
[4] H. A. Harwig, Z. anorg. allg. Chem. 444 (1978) 151
[5] R. D. Shannon, Acta Cryst. A 32 (1976) 751",
publisher = "Univerzitet u Beogradu, Tehnološko-metalurški fakultet",
journal = "8 th International Conference of the Chemical Societies of the South-East European Countries",
title = "Tm(III)-doped d-Bi2O3 for solid - oxide fuel cells",
pages = "188",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2890"
}
