Synthesis of silicon doped SrMO3 (M=Mn, Co): stabilization of the cubic perovskite and enhancement in conductivity

In this paper we report the successful incorporation of silicon into SrMO3 (M=Co, Mn) leading to a structural change from a hexagonal to a cubic perovskite. For M=Co, the cubic phase was observed for low doping levels (3%), and these doped phases showed very high conductivities ( up to ≈350 Scm-1 at room temperature). However, annealing studies at intermediate temperatures (700-800○C), indicated that the cubic phase was metastable with a gradual transformation to a hexagonal cell on annealing. Further work showed that co-doping with Fe resulted in improved stability of the cubic phase; a composition SrCo0.85Fe0.1Si0.05O3-y displayed good stability at intermediate temperatures and a high conductivity (≈150 Scm-1 at room temperature).\ud \ud For M=Mn, the work showed that higher substitution levels were required to form the cubic perovskite (≈15% Si doping), although in these cases the phases were shown to be stable to annealing at intermediate temperatures. Conductivity measurements again showed an enhancement in the conductivity on Si doping, although the conductivities were lower (≈0.3 – 14 Scm-1 in the range 20- 800○C) than the cobalt containing systems. The conductivities of both systems suggest potential for use as cathode materials in solid oxide fuel cells

Synthesis of oxyanion-doped barium strontium cobaltferrites: stabilization of the cubic perovskite and enhancement in conductivity

In this paper we demonstrate the successful incorporation of oxyanions (borate, phosphate) into Ba1ySryCo0.8Fe0.2O3−δ (BSCF) cathode materials. For low levels of dopant, a small enhancement in the conductivity was observed; e.g. 31.6, 34.4 and 35.9 S·cm-1 for Ba0.33Sr0.67Co0.8Fe0.2O3−δ, Ba0.33Sr0.67Co0.76Fe0.19B0.05O3−δ and Ba0.33Sr0.67Co0.76Fe0.19P0.05O3−δ, respectively, at 700ºC. Most significantly, oxyanion doping was shown to improve the stability of the cubic form of BSCF at intermediate temperatures (especially for P-doping), helping to prevent the transition to a hexagonal cell, and maintaining its excellent electrical properties. The work shows the potential of oxyanion doping strategies to modify the performance of SOFC cathode materials

Synthesis and characterization of oxyanion (phosphate, sulfate) doped Ba2_2Sc2_2−_-y_yGay_yO5_5

In this paper we examine the effect of partial substitution of Ga for Sc in the oxyanion (phosphate, sulfate) containing perovskites, Ba2Sc$_2$$_-$$_x$P$_x$O$_5$$_+$$_x$ and Ba$_2$S$_c$$_2$$_-$$_x$S$_x$O$_5$$_+$3$_x$$_/$$_2$ with the samples analysed through a combination of X-ray diffraction, TGA, Raman spectroscopy and conductivity measurements. The results demonstrate that in both cases, Ga can be incorporated in place of Sc up to 40%. In order to accommodate the increasing Ga content, a reduction in the oxyanion content is required. Thus for the highest Ga content sample achieved, only 10% oxyanion incorporation was achieved giving endmember compositions of Ba$_2$S$_c$Ga$_0$$_.$$_8$P$_0$$_.$$_2$O$_5$$_.$$_2$ and Ba$_2$S$_c$Ga$_0$$_.$$_8$S$_0$$_.$$_2$O$_5$$_.$$_3$ for phosphate and sulfate doping respectively. While the Ga doping was shown to significantly improve the stability of the systems towards CO$_2$ containing atmospheres, conductivity measurements showed a reduction in the conductivity with increasing Ga content

Synthesis, structure and conductivity of sulfate and phosphate doped SrCoO3

In this paper we report the successful incorporation of sulfate and phosphate into SrCoO3 leading to a change from a 2H– to a 3C–perovskite polymorph. Structural characterization by neutron diffraction showed extra weak peaks related to oxygen vacancy ordering, and these could be indexed on an expanded tetragonal cell, containing two inequivalent Co sites, similar to previously reported for Sb doped SrCoO3. Conductivity measurements on the doped systems showed a large enhancement compared to the undoped hexagonal system, consistent with corner–sharing of CoO6 octahedra for the former. Further work on the doped samples shows, however, that they are metastable, transforming back to the hexagonal cell on annealing at intermediate temperatures. The incorporation of Fe was shown, however, to improve the stability at intermediate temperatures, and these co–doped phases also showed high conductivities