Low temperature phase transitions of the SrMo1-xMxO3-δ (M = Mg and Ga) perovskites

SrMo1-xMgxO3-δ and SrMo1-xGaxO3-δ (x = 0.1 and 0.2) compounds have been demonstrated to possess excellent properties as anode materials in SOFC. Additionally, these perovskite oxides, cubic at room temperature, exhibit low-temperature phase transitions that have been characterized by neutron powder diffraction (NPD) at 298, 200 and 2 K. Two phase transitions have been identified in both families: one to a tetragonal structure with I4/mcm space group and the second one to an orthorhombic Imma phase. The first one was observed near 270 K by an inflection in the magnetic susceptibility; the second one occurs between 200 and 2 K. The sequence involves a progressive increase of the (Mo,Mg)O6 or (Mo,Ga)O6 octahedra rotation, throughout one (I4/mcm) or two (Imma) of the pseudocubic axes. The magnetic properties suggest a Pauli paramagnetism for all the compounds.