NDLI: Investigation into the effect of Si doping on the performance of $Sr_{1−y}Ca_{y}MnO

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Slater, Peter R. Kemp, Thomas F. Porras-vazquez, Jose M. Keenan, Philip J. Hancock, Cathryn A. Losilla, Enrique R. Hanna, John V.
Description	Author Affiliation: Porras-Vazquez JM ( School of Chemistry, University of Birmingham, Birmingham, B15 2TT, UK. j.m.porras@bham.ac.uk)
Abstract	In this paper we report the successful incorporation of silicon into $Sr_{1−y}Ca_{y}MnO_{3−δ}$ perovskite materials for potential applications in cathodes for solid oxide fuel cells. The Si substitution onto the B site of a $^{29}Si$ enriched $Sr_{1−y}Ca_{y}Mn_{1−x}Si_{x}O_{3−δ}$ perovskite system is confirmed by $^{29}Si$ MAS NMR measurements at low $B_{0}$ field. The very large paramagnetic shift (∼3000–3500 ppm) and anisotropy (span ∼4000 ppm) suggests that the $Si^{4+}$ species experiences both Fermi contact and electron-nuclear dipolar contributions to the paramagnetic interaction with the $Mn^{3+/4+}$ centres. An improvement in the conductivity is observed for low level Si doping, which can be attributed to two factors. The first of these is attributed to the tetrahedral coordination preference of Si leading to the introduction of oxide ion vacancies, and hence a partial reduction of $Mn^{4+}$ to give mixed valence Mn. Secondly, for samples with high Sr levels, the undoped systems adopt a hexagonal perovskite structure containing face sharing of $MnO_{6}$ octahedra, while Si doping is shown to help to stabilise the more highly conducting cubic perovskite containing corner linked octahedra. The level of Si, x, required to stabilise the cubic $Sr_{1−y}Ca_{y}Mn_{1−x}Si_{x}O_{3−δ}$ perovskite in these cases is shown to decrease with increasing Ca content; thus cubic symmetry is achieved at x = 0.05 for the $Sr_{0.5}Ca_{0.5}Mn_{1−x}Si_{x}O_{3−δ}$ series; x = 0.075 for $Sr_{0.7}Ca_{0.3}Mn_{1−x}Si_{x}O_{3−δ};$ x = 0.10 for $Sr_{0.8}Ca_{0.2}Mn_{1−x}Si_{x}O_{3−δ};$ and x = 0.15 for $SrMn_{1−x}Si_{x}O_{3−δ}.$ Composites with 50% $Ce_{0.9}Gd_{0.1}O_{1.95}$ were examined on dense $Ce_{0.9}Gd_{0.1}O_{1.95}$ pellets. For all series an improvement in the area specific resistances (ASR) values is observed for the Si-doped samples. Thus these preliminary results show that silicon can be incorporated into perovskite cathode materials and can have a beneficial effect on the performance.
ISSN	14779226
Issue Number	15
Journal	Dalton Trans.
Volume Number	42
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2013-04-21
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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