A comprehensive variable temperature study of the layered oxide, Ca2Mn3O8

Ca2Mn3O8 forms a delafossite-related layered structure, which crystallises with monoclinic C2/m symmetry. Compared with the delafossite-structure, the MnO6 layers in Ca2Mn3O8 exhibit an ordered cation void which forms a magnetic ‘bow-tie’ like connectivity of Mn4+ ion layers separated by Ca2+ ions. In-situ variable temperature diffraction data demonstrates that the structure is robust up to a temperature of approximately 1173 K before the material decomposes into the perovskite, CaMnO3 and marokite, CaMn2O4 phases. Simultaneous thermal analysis suggests that a very small amount of water remains within the layers post synthesis. Impedance spectroscopy indicates that Ca2Mn3O8 is an electronic conductor in the range ∼400–700 K with an activation energy of 0.50 ± 0.01 eV.