Role of SrMoO4 in Sr2MgMoO6 synthesis

Here we investigate the elemental and phase compositions during the solid-state synthesis of the promising SOFC-anode material, Sr2MgMoO6, and demonstrate that molybdenum does not notably evaporate under the normal synthesis conditions with temperatures up to 1200 °C due to the formation of SrMoO4 as an intermediate product at low temperatures, below 600 °C. However, partial decomposition of the Sr2MgMoO6 phase becomes evident at the higher temperatures (∼1500 °C). The effect of SrMoO4 on the electrical conductivity of Sr2MgMoO6 is evaluated by preparing a series of Sr2MgMoO6 samples with different amounts of additional SrMoO4. Under the reducing operation conditions of an SOFC anode the insulating SrMoO4 phase is apparently reduced to the highly conductive SrMoO3 phase. Percolation takes place with 20–30 wt% of SrMoO4 in a Sr2MgMoO6 matrix, with a notable increase in electrical conductivity after reduction. Conductivity values of 14, 60 and 160 S/cm are determined at 800 °C in 5% H2/Ar for the Sr2MgMoO6 samples with 30, 40 and 50 wt% of added SrMoO4, respectively.

Graphical abstractSrMoO4 is formed at low temperatures during the synthesis of Sr2MgMoO6, which prevents the volatilization of Mo from typical precursor mixtures of this promising SOFC anode material. SrMoO4 is insulating and it is often found as an impurity in Sr2MgMoO6 samples. It is however readily reduced to highly conducting SrMoO3. Composites of Sr2MgMoO6 and SrMoO3 show increased electrical conductivities compared to pure Sr2MgMoO6 under the reductive operation conditions of an SOFC anode.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sr2MgMoO6 is a promising SOFC anode material. ► During the Sr2MgMoO6 synthesis SrMoO4 is formed at low temperatures. ► Formation of SrMoO4 effectively prevents volatilization of Mo at high temperatures. ► Insulating SrMoO4 reduces to highly conductive SrMoO3 under SOFC-anode conditions. ► Composites of Sr2MgMoO6 and SrMoO3 show high electrical conductivities.