Thermal expansion and electrical conductivity of Fe and Cu doped MnCo2O4 spinel

Abstract

Manganese cobalt spinel oxides are promising coating materials for corrosion protection of metallic interconnects in solid oxide fuel cell stacks. This work investigates how Fe and Cu doping affect the crystal structure, thermal expansion and electrical conductivity of the MnCo2-xMxO4 (M=Cu, Fe; x = 0.1, 0.3, 0.5) spinel oxides. Single phase cubic spinels were successfully prepared by spray pyrolysis. The electrical conductivity between room temperature and 1000 °C increased with addition of Cu and decreased with addition of Fe. The thermal expansion coefficient (TEC) between 50 and 800 °C decreased from 14.4 to 11.0×10-6 K-1 going from MnCo2O4 to MnCo1.5Fe0.5O4. The TEC of the Cu substituted materials did not follow any obvious trend with composition and was likely influenced by precipitation of CuO during heating. Based on their physical properties, the Fe doped materials are the most attractive for application as SOFC interconnect coatings.

Electrophoretic co-deposition of Fe2O3 and Mn1,5Co1,5O4: Processing and oxidation performance of Fe-doped Mn-Co coatings for solid oxide cell interconnects

“…Currently, many studies are focusing on the possibility to improve the (Mn,Co)3O4 spinel further by transition metal doping, in particularly with Fe or/and Cu [44,[47][48][49][50][51][52][53][54][55]. Since the coating properties are strongly affected by the preparation procedure, there is considerable scatter in the literature results.…”

“…Nevertheless, there is evidence that Fe-doping reduces the TEC of (Mn,Co)3O4, thus improving the thermo-mechanical compatibility with the substrate. For example, Talic et al [49] found that the TEC decreased with Fe-doping from 14.4 × 10 -6 K -1 for MnCo2O4 to 11.0 × 10 -6 K -1 for MnCo1.5Fe0.5O4. In terms of oxidation resistance, it is not clear whether Fe-doping has a beneficial effect.…”

Interface Fracture Energy of Contact Layers in a Solid Oxide Cell Stack

“…After the relatively short heat treatment (10 h at 900 °C), Cu from the CuMn foam was found at the original coating/oxide scale interface, corresponding to a diffusion distance of ~10 µm. In addition to creating a very strong bond, the incorporation of Cu in the (Mn,Co) 3 O 4 spinel has the benefit of increasing the electrical conductivity [45]. However, in areas of the coating where Cu had diffused, there was also a higher concentration of Cr, which had diffused outward from the alloy.…”

Formulation of spinel based inkjet inks for protective layer coatings in SOFC interconnects

“…However, the performance of the mentioned spinel compositions was improved by the substitution of Co with Fe and Cu . Addition of Fe and Cu in MnCo2O4 spinel system has shown an improved coefficient of thermal expansion (CTE) matching better with that of the ferritic stainless-steel substrates and with higher electrical conductivity, respectively [12,19,20]. The thermal behaviour of ferrite substituted into spinels has been studied in other contexts [21].…”