The phase relation, diffusivity, and electrical conductivity are investigated for powders and dense crystalline bodies of manganese-chromium-iron oxides with spinel structure which is regarded as main compounds in the oxide scale of some ferritic alloy interconnects of solid oxide fuel cells (SOFC). The lattice parameter of MnCr2O4-based spinel oxide increased with iron substitution for chromium at B-site. The iron substitution greatly improved the electrical conductivity. The fast cation diffusion was observed for iron substituted samples forming an iron-rich layer in the vicinity of surface. The compatibility of some ferritic alloys as SOFC interconnects is evaluated by using conductivity data of Mn-Cr-Fe spinels. (C) 2004 Elsevier B.V. All rights reserved.