Synthesis, electrical properties and thermal analysis of transition metal-doped Mg2TiO4 spinels

The synthesis and characterization of Mg2TiO4 doped with different transition elements (Mn, Fe, Co) are reported. Three different series of cubic spinel titanate are obtained by substitution of only one cation (Mg2−xMxTiO4, Mg2Ti1−xMxO4) or both cations (Mg2−x/2Ti1−x/2MxO4) for x=0.1 and their electrical properties have been compared. AC conductivity data have been measured in air between 500 and 1000°C, showing for all the samples an Arrhenius dependence. Activation energy and conductivity are similar to Mg2TiO4 (Ea=0.28 eV, σ∼10−3 S m−1) for M=Fe, Co, although conductivity is slightly higher for M=Mn. The DC conductivity was recorded over a wide range of oxygen partial pressures (10−19 to 1 atm.) at 930°C. The Co and Fe compounds show a n-type behaviour whereas the Mn compounds show a pseudo p-type behaviour at high pO2 and n-type at low pO2. Conductivity at very low pO2 is in the region 101–10−1 S m−1 for all the samples investigated.