A stabilization mechanism for the perovskite La2/3TiO3 compound with Fe2O3: A structural and electrical investigation

We have stabilized the perovskite La2/3TiO3 by adding LaFeO3 and shown that in general the stabilization mechanism for the (1 − x)La2/3TiO3–xLaFeO3 mixture involves the formation of a solid solution for compositions with x ≥ 0.04. The crystal structure of the solid solution transforms from orthorhombic to tetragonal at x = 0.2, becomes cubic in the range 0.3 < x < 0.8, and transforms again into orthorhombic (typical for pure LaFeO3) for values greater than 0.8. Detailed impedance-spectroscopy measurements for various compositions and conditions showed that the limiting step in the conduction mechanism was conduction across the grain boundaries. In the concentration range 0.04 < x < 0.25 the room temperature conductivity increases up to 0.0017 S cm−1, after which it decreases again. Part of the initial increase is probably due to the formation of free electrons in accordance with (FeTi)′ → (FeTi)x + n′. Other defect-formation mechanisms are also discussed, but are ruled out for a variety of reasons. Another interesting phenomenon that also affected the average conductivity was identified, i.e., the variation of the average particle size with composition.