Unravelling the low thermal expansion coefficient of cation-substituted YBaCo4O7+δ

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With an aim to understand the origin of the low thermal expansion coefficients (TECs), cation-substituted YBaCo4O7-type oxides have been investigated by in-situ neutron diffraction, bond valence sum (BVS), thermogravimetric analysis, and dilatometry. The compositions YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ were synthesized by solid-state reaction at 1200°C. Rietveld refinement of the joint synchrotron X-ray and neutron diffraction data shows that the Zn and Fe dopants have different preferences to substitute the Co ions in the 6c and 2a sites. The bulk thermal-expansion coefficients of YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ are, respectively, 9.42, 9.76, and 9.06 × 10-6°C-1. Neutron diffraction data show that the low anisotropic TEC along the a-axis is the main contributor to the low bulk TECs. With the substitution of In, Zn, and Fe in Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ, the anisotropic and bulk TECs could be reduced to 8.94 and 9.06 × 10-6°C-1, respectively, mainly due to the suppression of the change in Co-O bond length in CoO4 polyhedra. The observed weight loss during heating is due to the loss of interstitial oxide ions, as revealed by neutron diffraction and BVS map. Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ has the lowest area-specific cathodic polarization resistance of 0.14 Ω cm2 (Rtotal/2) at 700°C in air.




Kan, W. H., Lai, K. Y., Huq, A., & Manthiram, A. (2016). Unravelling the low thermal expansion coefficient of cation-substituted YBaCo4O7+δ. Journal of Power Sources, 307, 454–461. https://doi.org/10.1016/j.jpowsour.2016.01.017

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