Structure, electrical conducting and thermal expansion properties of Ln_0.6Sr_0.4Co_0.8Fe_0.2O₃ (Ln=La, Pr, Nd, Sm) ceramics

Abstract

Ln_0.6Sr_0.4Co_0.8Fe_0.2O₃ (Ln=La, Pr, Nd, Sm) perovskite-type complex oxides were synthesized using a glycine-nitrate process, and the structure, electrical conducting and thermal expansion properties of the resulting ceramics were examined with regard to the nature of the lanthanide cations. The results indicated that the La, Pr and Nd specimens had a rhombohedral symmetry, while an orthorhombic structure was determined for the Sm specimen. The pseudo-cubic lattice constant decreased with smaller lanthanide cations. It was found that the electrical conducting properties declined with decreasing lanthanide cation size. Fortunately, all the compositions remained rather high electrical conductivities exceeding 650 Ω⁻¹·cm⁻¹ in the intermediate temperature range (600–800 °C). An appreciable thermal expansion increase at high temperatures was detected for all the compositions. Decreasing the size of the lanthanide cations resulted in an increase of thermal expansion. With respect to the high electrical conductivities, the Ln_0.6Sr_0.4Co_0.8Fe_0.2O₃ oxides are considered to be acceptable as mixed conducting component in composite cathode designs together with doped ceria electrolytes.

Keywords

electrical conduction / Perovskites / thermal expansion

References

[1] Teraoka Y., Zhang H. M., Okamoto K., . Mixed Ionicelectronic Conductivity of La_1−xSr_xCo_1−yFe_yO_3−δ Perovskite-type Oxides[J]. Mater. Res. Bull., 1988, 23: 51-58.

[2] Beson S. J., Waller D., Kilner J. A. Degradation of La_0.6Sr_0.4Fe_0.8Co_0.2O_3−δ in Carbon Dioxide and Water Atmospheres[J]. J. Electrochem. Soc., 1999, 146: 1 305-1 309.

[3] Tsai C. Y., Dixon A. G., Ma Y. H., . Dense Perovskite, La_1−xA′_xFe_1−yCo_yO₃-Delta (A′=Ba, Sr, Ca), Membrane Synthesis, Applications, and Characterization[J]. J. Am. Ceram. Soc., 1998, 81: 1 437-1 444.

[4] Tu H. Y., Takeda Y., Imanishi N., . Ln_0.4Sr_0.6Co_0.8Fe_0.2O_3−δ (Ln =La, Pr, Nd, Sm) for the Electrode in Solid Oxide Fuel Cells[J]. Solid State Ionics, 1999, 117: 277-281.

[5] Qiu L., Ichikawa T., Hirano A., . Ln_1−xSr_xCo_1−yFe_yO_3−δ (Ln=Pr, Nd, Gd; x=0.2, 0.3) for the Electrodes of Solid Oxide Fuel Cells[J]. Solid State Ionics, 2003, 158: 55-65.

[6] Kharton V. V., Kovalevsky A. V., Viskup A. P., . Oxygen Transport in Ce_0.8Gd_0.2O_2−δ-based Composite Membranes[J]. Solid State Ionics, 2003, 160: 247-258.

[7] Riza F., Ftikos C., Tietz F., . Preparation and Characterization of Ln_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ (Ln=La, Pr, Nd, Sm, Eu, Gd)[J]. J. Eur. Ceram. Soc., 2001, 21: 1 769-1 773.

[8] Dasgupta N., Krishnamoorthy R., Jacob K. T. Crystal Structure, Thermal Expansion and Electrical Conductivity of Nd_0.7Sr_0.3Fe_1−xCoxO₃(0≤x≤0.8)[J]. Mater. Sci. Eng. B., 2002, 90: 278-286.

[9] Dyck C. R., Peterson R. C., Yu Z. B., . Crystal Structure, Thermal Expansion and Electrical Conductivity of Dual-phase Gd_0.8Sr_0.2Co_1−yFe_yO_3−δ (0≤y≤1.0)[J]. Solid State Ionics, 2005, 176: 103-108.

[10] Wang S. R., Kato T., Nagata S., . Performance of a La_0.6Sr_0.4Co_0.8Fe_0.2O₃-Ce_0.8Gd_0.2O_1.9-Ag Cathode for Ceria Electrolyte SOFCs[J]. Solid State Ionics, 2002, 146: 203-210.

[11] Katsuki M., Wang S. R., Dokiya M., . High Temperature Properties of La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ Oxygen Nonstoichiometry and Chemical Diffusion Constant[J]. Solid State Ionics, 2003, 156: 453-461.

[12] Xu Q., Huang D. P., Chen W., . Citrate Method Synthesis, Characterization and Mixed Electronic-ionic Conduction Properties of La_0.6Sr_0.4Co_0.8Fe_0.2O₃ Perovskite-type Complex Oxides[J]. Scripta Mater., 2004, 50: 165-170.

[13] Xu Q., Huang D. P., Chen W., . Influence of Sintering Temperature on Microstructure and Mixed Electronic-ionic Conduction Properties of Perovskite-type La_0.6Sr_0.4Co_0.8Fe_0.2O₃ Ceramics[J]. Ceram. Int., 2004, 30: 429-433.

[14] Tai L. W., Nasrallah M. M., Anderson H. U., . Structural and Electrical Properties of La_1−xSr_xCo_1−yFeyO₃, Part 1[J]. Solid State Ionics, 1995, 76: 259-271.

[15] Tai L. W., Nasrallah M. M., Anderson H. U., . Structural and Electrical Properties of La_1−xSr_xCo_1−yFe_yO₃, Part 2[J]. Solid State Ionics., 1995, 76: 273-283.

[16] Kostogloudis G. C., Ftikos C. Properties of A-site-deficient La_0.6Sr_0.4Co_0.2Fe_0.8O₃-based Perovskite Oxides[J]. Solid State Ionics, 1999, 126: 143-151.

[17] Stevenson J. W., Armstrong T. R., Carneim R. D., . Electrochemical Properties of Mixed Conduting Perovskite La_1−xM_xCo_1−yFe_yO_3−δ (M=Sr, Ba, Ca)[J]. J. Electrochem. Soc., 1996, 143: 2 722-2 729.

[18] Uhlenbruck S., Tietz F. High-temperature Thermal Expansion and Conductivity of Cobaltites: Potentials for Adaptation of the Thermal Expansion to the Demands for Solid Oxide Fuel Cells[J]. Mater. Sci. Eng. B, 2004, 107: 277-282.

[19] Deng Z. Q., Zhang G. G., Liu W., . Phase Composition, Oxidation and Electrical Conductivity of SrFe_1.5−xCo_xO_y[J]. Solid State Ionics, 2002, 152–153: 735-739.

[20] Torrance J. B., Lacorre P., Nazzal A. I., . Systematic Study of Insulator-metal Transition in Perovskite RNiO₃ (R=Pr, Nd, Sm, Eu) due to Closing of Charge-transfer Gap[J]. Phys. Rev. B, 1992, 45: 8 209-8 212.

[21] Cherif K., Dhahri J., Dhahri E., . Effect of the A Cation Size on the Structural, Magnetic, and Electrical Properties of Perovskites (La_1−xNd_x)_0.7Sr_0.3MnO₃[J]. J. Solid State Chem., 2002, 163: 466-471.

[22] Kostogloudis G. C., Fertis P., Ftikos C. The Perovskite Oxide System Pr_1−xSr_xCo_1−yMn_yO_3−δ: Crystal Structure and Thermal Expansion[J]. J. Eur. Ceram. Soc., 1998, 18: 2 209-2 215.

[23] Kharton V. V., Yaremchenko A. A., Patrakeev M. V., . Thermal and Chemical Induced Expansion of La_0.3Sr_0.7(Fe, Ga)O_3−δ Ceramics[J]. J. Eur. Ceram. Soc., 2003, 23: 1 417-1 426.

[24] Dusastre V., Kilner J. A. Optimisation of Composite Cathodes for Intermediate Temperature SOFC Applications[J]. Solid State Ionics, 1999, 126: 163-174.