Solid-State 29Si NMR and Neutron-Diffraction Studies of Sr0.07K0.3SiO2.85 Oxide Ion Conductors

Published

July 7, 2014

Author(s)

Jungu Xu, Xiaoming Wang, Hui Fu, Craig Brown, Xiping Jing, Fuhui Liao, Fengqi Lu, Xiaohui Li, Xiaojun Kuang, Mingmei Wu

Abstract

The new oxide ion conductors Sr_1-xK_xSiO_3-05x, recently reported as promising candidate electrolytes for solid oxide fuel cells, were characterized using solid-state ²⁹Si nuclear magnetic resonance (NMR)spectroscopy, neutron powder diffraction (NPD) and variable temperature X-ray diffraction (VT-XRD). Differing with the average structure containing the vacancies stabilized within the isolated Si₃O₉ tetrahedral rings derived from the NPD study, the ²⁹Si NMR data provide new insight into the local defect structure in Sr_1-xK_xSiO_3-05.x. The Q¹-linked tetrahedral Si signal in the ²⁹Si NMR data suggest that the Si₃O₉ tetrahedral rings in the K-doped SrSiO_{3 materials were broken by removing the bridging oxygen atoms, forming Si}d3^O₈ chains, consistent with the oxide vacancy preferences on bridging sites over the terminal sites from NPD data refinement. The Si₃O₈ chains can be stabilized by either bonding with the oxygen atoms of absorbed water molecules, leading to the Q¹-linked tetrahedral Si, or sharing oxygen atoms with neighbouring Si₃O₉ units, which is consistent with the Q³-linked tetrahedral Si signal in the ²⁹Si NMR spectra. In addition to the linkage of Si₃O₈ chains with Si₃O₉ rings, condensation of Si₃O₉ rings via local rotating and distorting the rings for corner-sharing are also discussed. VT-XRD measurement showed an instability gap between 700 °C and 1000 °C for Sr_1-xK_xSiO_3-0.5x. Both the VT-XRD and conductivity data revealed that a firing temperature above 1100 Degree}C is favourable for stabilizing the K-doped SrSiO₃ materials as single phase on cooling and that the defect structure in the K-doped SrSiO₃ materials is temperature dependent.

Citation

Inorganic Chemistry

Volume

53

Pub Type

Journals

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Keywords

Neutron diffraction, NMR, X-ray diffraction, oxide conductor

Citation

Xu, J. , Wang, X. , Fu, H. , Brown, C. , Jing, X. , Liao, F. , Lu, F. , Li, X. , Kuang, X. and Wu, M. (2014), Solid-State ²⁹Si NMR and Neutron-Diffraction Studies of Sr_0.07K_0.3SiO_2.85 Oxide Ion Conductors, Inorganic Chemistry, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=915719 (Accessed May 18, 2024)