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Research Papers

Relationship Between Oxide-Ion Conductivity and Ordering of Oxygen Vacancy in the Ln2 Zr2 O7 (Ln = La, Nd, Eu) System Using High Temperature XRD

[+] Author and Article Information
Takeshi Hagiwara1

 Research Institute for Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japanhagi@kanagawa-u.ac.jp

Hiroshi Yamamura, Hanako Nishino

Department of Material and Life Chemistry,  Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

1

Corresponding author.

J. Fuel Cell Sci. Technol 8(5), 051020 (Jul 12, 2011) (5 pages) doi:10.1115/1.4003785 History: Received January 21, 2011; Revised January 27, 2011; Published July 12, 2011; Online July 12, 2011

The pyrochlore-type Ln2 Zr2 O7 (Ln = La, Nd, Eu) systems were refined by Rietveld analyses of XRD data combined with the MEM-based pattern fitting at RT, 873, 1073, and 1273 K. All the samples kept a single cubic phase of the pyrochlore-type structure in the temperature range up to 1273 K. The oxide-ion conductivities of the present systems were discussed on a basis of ordering of oxygen vacancy in the pyrochlore-type structure. Theoxide-ion conduction of Eu2 Zr2 O7 was ascribed to diffusion of oxygen along the 100 direction, while the hole conduction of La2 Zr2 O7 occurred along the 110 direction, according to the charge density map estimated by the MEM analysis.

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Figures

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Figure 1

XRD patterns in the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system at 1273 K

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Figure 2

Rietveld analysis of XRD data of Eu2 Zr2 O7 at 1073 K on the basis of the two models. The charge density maps in (100) plane calculated by MEM analysis were written.

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Figure 3

Temperature dependences of lattice constants obtained from the Rietveld analyses of the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system as a function of temperature. The broken lines represent the thermal expansion ratio between RT and each temperature. •,○: Ln = La, ▪,□: Ln = Nd, ▴,▵: Ln = Eu.

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Figure 4

Temperature dependences of the occupancies for oxygen 8b site of the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system. •: Ln = La, ▪: Ln = Nd, ▴: Ln = Eu.

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Figure 5

Arrhenius plots of the electrical conductivity of the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system. •: Ln = La, ▪: Ln = Nd, ▴: Ln = Eu.

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Figure 6

The electrical conductivity at 1073 K and the occupancy of oxygen 8b site as a function of cation radius ratio for the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system

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Figure 7

The charge density calculated by MEM analysis at 1073 K in (110) plane, which shows cation sites, oxygen 8a, 8b, and 48f sites of the Ln2 Zr2 O7 (Ln = La, Nd, Eu) system. The contour lines of the charge density are 1000 and 1250 e nm−3 .

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Figure 8

The charge density calculated by MEM analysis at each temperature in (110) plane, which shows cation sites, oxygen 8a, 8b, and 48f sites of the Eu2 Zr2 O7. The contour lines of the charge density are 1000 and 1250 e nm−3 .

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Figure 9

The charge density calculated by MEM analysis at each temperature in (110) plane, which shows cation sites, oxygen 8a, 8b, and 48f sites of the La2 Zr2 O7. The contour lines of the charge density are 1000 and 1250 e nm−3 .

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