Effect of Si-Doping on the Structure and Conductivity of (Sr/Ca)₂MnFeO_6-δ Systems

Abstract

Following previous work on silicate doping of perovskite (Sr/Ca)MnO3 and (Sr/Ca)FeO3- δ materials for potential application as electrode materials for solid oxide fuel cells, here we report the successful incorporation of silicon into the mixed Mn/Fe systems, (Sr/Ca)2MnFeO6-δ. The results show a higher level of Si doping to be possible for Ca2MnFe1-xSixO6— δ (0≤x≤0.4) compared to Sr2MnFe1-xSixO6— δ (0≤x≤0.2). In both cases, the conductivity is improved for low doping levels (x≤0.1), with a subsequent decrease for higher doping levels. Additional preliminary work has shown that phosphate can also be successfully incorporated into these perovskite systems. The work therefore further illustrates the potential of oxyanion doping in perovskite systems of interest for Fuel Cell applications.

Synthesis and Characterisation of P-Doped Sr2MnFeO6-δ Systems

“…This reduction is attributed to presence of Sr3(PO4)2 impurities as the solubility limit is exceeded. Overall, the conductivities of the Sr2MnFe0.95P0.05O5.41were higher than the undoped and silicate perovskite structure reported by Smith et al, Table IV (32).…”

“…The Mn/Fe site oxidation state was shown to be lower than reported previously for Si doped materials. 32 57 Fe Mössbauer data were collected for the x=0 and 0.05 samples to gain further information on the Fe environment. Chemical isomer shifts δ ≈ -0.23, 0.22/0.23 and 0.31/0.36 mm s -1 (Fe/ Fe0.95P0.05) can be assigned to Fe 5+ , Fe 4+ and Fe 3+ respectively (Figure 4 and Table II).…”

“…(29)(30)(31). Previous work by Smith et al showed a related silicon doping strategy was successful in synthesising Sr2MnFe1-xSixO6-δ with the formation of a single-phase cubic perovskite structure (32). The conductivity was shown to be improved with low levels of Si doping ( 0.1), with a decrease at higher silicate levels.…”

Synthesis and Characterization of Phosphate Doped BaPr1-y(Y/Yb/Tm)yO3-δ

“…In addition to this oxyanion doping has been shown to enhance the CO2 stability of the doped Ba2(In/Sc)2O5 systems, which is attributed to the introduction of these acidic dopants reducing the basicity of the system [11][12][13][14]. These oxyanion dopants have also been shown to be able to be accommodated into a range of other perovskites, both electrolyte and electrode systems, showing that the perovskite structure is amenable to their incorporation [15][16][17][18][19][20][21][22][23].…”

Investigation of PO43− oxyanion-doping on the properties of CaFe0.4Ti0.6O3−δ for potential application as symmetrical electrodes for SOFCs

“…Recently, the properties of simple perovskites (ABO 3 ) have been modified by the incorporation of oxyanions, such as BO 4 , into the ionic framework [31][32][33][34]. Under this approach, the octahedral BO 6 unit is replaced by a tetrahedral oxyanion, and therefore, generating two oxide vacancies that favours the ionic conductivity.…”