Order-disorder enhanced oxygen conductivity and electron transport in Ruddlesclen-Popper ferrite-titanate Sr3Fe2-xTixO6+δ

The Ruddlesden-Popper ferrite Sr3Fe2O6+delta and its titaniadoped derivatives Sr3Fe2-xTiO6+delta, where O<xless than or equal to2, have been characterized by X-ray powder diffraction and thermogravimetry. The changes in oxygen content and crystal lattice parameters are consistent with titanium ions entering the solid solution in 4+ oxidation state with octahedral oxygen coordination. Electronic conductivity measurements on polycrystalline Sr3Fe2O6+delta and Sr3Fe0.8Ti1.2O6-delta in the temperature range 750-1000degreesC and oxygen partial pressures (pO(2)) varying between 10(-20) and 0.5atm revealed that the predominant partial conductivity of electrons is proportional to pO(2) (-1/4) in the low pO(2) region, while the predominant partial contribution of holes to the conductivity is proportional to PO2+1/4 in the 2 high PO2 range. The pressure-independent oxygen ion conductivity is found to decrease with the increase in titanium content. A possible pathway for oxygen ion migration is discussed in relation to disorder in the oxygen sublattice and titanium doping. (C) 2002 Elsevier Science (USA).