Preparation, characterization and electrical property of Mn-doped ceria-based oxides

doi:10.1016/j.ssi.2006.04.016

Solid State Ionics

Volume 177, Issues 19–25, 15 October 2006, Pages 1799-1802

https://doi.org/10.1016/j.ssi.2006.04.016 Get rights and content

Abstract

Manganese-doped ceria-based oxides, Ce_1−xMn_xO_2−δ (0.05 ≤ x ≤ 0.3) and Ce_1−x−yGd_xMn_yO_2−δ˙ (0.05 ≤ x≤ 0.2, 0.05 ≤ y ≤ 0.25) were synthesized, and crystal phase analysis by XRD and measurements of electrical properties were performed. Solubility limit of Mn in Ce_1−xMn_xO_2−δ˙ seemed to be between 5 mol% and 10 mol% and Mn₃O₄ was the main by-product above the solubility limit in the case of heat treatment at 1300 °C. Judging from the oxygen partial pressure dependence of total conductivity and emf measurements, Ce_1−xMn_xO_2−δ˙ is a single-phase mixed conductor within the composition below the solubility limit, and when the composition of Mn exceeds the solubility limit, it becomes the dual-phase mixed conductor of Ce_1−xMn_xO_2−δ˙ and Mn₃O₄. The doing of Mn in gadlia-doped ceria, Ce_1−x−yGd_xMn_yO_2−δ˙ (0.05 ≤ x ≤ 0.2, 0.05 ≤ y ≤ 0.25), was more difficult than that in CeO₂ presumably due to the preferential reaction between Gd and Mn to give GdMnO₃ to the GDC solid solution formation, and the Mn doping seems not to be so effective in preparing the mixed ionic–electronic conductor based on GDC.

Introduction

Mixed ionic–electronic conductors (MIECs) are materials that conduct both ionic and electronic (electron and/or hole) charge carriers. MIECs of metal oxides which show high oxide ionic and electronic conductivities have been attracting a great deal of attention, because they have high potentiality as pressure-driven oxygen permeation membranes [1]. In addition, oxygen-permeable MIECs can find application in membrane reactors catalyzing, for example, NOx removal reactions (2NO → N₂ + O₂, 4NO + CH₄ → 2N₂ + CO₂ + 2H₂O, etc) and partial oxidation of methane (2CH₄ + O₂ → 2CO + 4H₂) [1], [2]. These MIEC membrane devices should become promising technologies in environmental- and energy-related fields, if the improvement of the performance will be realized by the development of more excellent materials, improvement of material and device processing, and so on.

Co-containing perovskite type-oxides have been examined as oxygen separation membrane. Although they generally show excellent mixed conductivity, they are weak against reduction, especially, for the use of membrane reactors fed with reducing reactants. Ceria (CeO₂) with fluorite-type structure is known to tolerate a considerable reduction without phase change and also known to show relatively high oxide ion conductivity. In addition, the reduction of Ce⁴⁺ results in the simultaneous formation of oxide ion vacancy and Ce³⁺ in the bulk (Eq. (1)) [1], [3], [4], causing the appearance of electronic conductivity and thus being a mixed conductor. $O_{O}^{X} + 2 {Ce}_{Ce}^{X} \to V_{O}^{• •} + 2 {Ce}_{Ce}' + (1 / 2) O_{2} (g)$ Ce_Ce^X; Ce⁴⁺, Ce_Ce^′; Ce³⁺; V_O^••; oxide ion vacancy

The mixed conductivity of ceria-based materials might be enhanced when a transition metal ion, the valence of which is lower than 4+, is incorporated into ceria to form a solid solution; increases in the amount of oxide ion vacancies by the substitution with a lower-valence cation and the electronic conductivity originating from the nature of a transition metal ion might be expected. Based on this strategy, the preparation, structural characterization and electrical property of the Mn-doped CeO₂ was investigated in this paper. In addition, since CeO₂–Gd₂O₃ solid solution (GDC) is known to exhibit more excellent ionic conductivity than CeO₂ [5], GDCs were also used as host materials of Mn doping.

Section snippets

Synthesis and structural characterization of ceria-based MIEC

Powders of Ce_1−xMn_xO_2−δ (0.05 ≤ x ≤ 0.3) and Ce_1−x−yGd_xMn_yO_2−δ˙ (0.05 ≤ x ≤ 0.2, 0.05 ≤ y ≤ 0.25) were prepared from nitrates of constituent metals by the RHP (reverse homogeneous precipitation) method using aqueous ammonia [6]. The precipitates were collected by filtration, dried at 110 °C for 12 h, pre-calcined at 350 °C for 2 h, and finally calcined at 800 °C for 10 h in air to obtain powder samples. Sintered disks were obtained by uniaxial (180 MPa, 5 min) and isostatic (253 MPa, 1 h) pressing methods

Crystal phase analysis

Fig. 1(a) shows XRD patterns of Ce_1−xMn_xO_2−δ (0.05 ≤ x ≤ 0.3) prepared at 1300 °C. By-produced Mn₃O₄ was clearly observed in addition to the main fluorite phase for Ce_1−xMn_xO_2−δ (x ≥ 0.2), but not for x = 0.05. For intermediate composition (x = 0.1–0.15), trace amounts of Mn₃O₄ were observed. Phase analysis results by XRD of Ce_1−xMn_xO_2−δ (0.05 ≤ x ≤ 0.3) are summarized in Table 1. In ESR spectra of Ce_1−xMn_xO_2−δ (Fig. 2), sextet lines characteristic to isolated Mn²⁺ were observed. Such isolated,

Conclusion

The solubility limits of Mn-doped ceria-based oxides, Ce_1−xMn_xO_2−δ˙ seemed to be between 5 mol% and 10 mol% after sintered at 1300 °C. The electrical property of the Mn-doped ceria depended significantly on the composition (x) of Mn as well as the partial pressure of O₂ in the atmosphere. Total conductivities in both air and O₂ atmospheres tended to increase with increasing Mn content. The semiconducting nature estimated from the effect of oxygen partial pressures on total conductivity changed

References (7)

H.J.M. Bouwmeester et al.
M. Mogensen et al.
Solid State Ionics
(2000)
R.M. Dell et al.

There are more references available in the full text version of this article.

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