Characteristics of mixed conducting perovskites (Ba1−xNdx)Fe3+1−tFe4+tO3−y

To study the characteristics of (Ba2+1−xNd3+x)Fe3+1−tFe4+tO3−y perovskite system with x = 0.0 (BN-0), 0.1 (BN-1), 0.2 (BN-2) and 0.3 (BN-3), heat-treatments were performed in N2 (1 atm), air, and O2 (1 atm) at 1273 K for 24 h (slowly cooling (cooling rate = 20 K/h)). X-ray powder diffraction assured that the four samples heat-treated in air had cubic symmetries (BN-0: 4.033 Å, BN-1: 4.014 Å, BN-2: 4.001 Å, and BN-3: 3.989 Å) and that the lattice volumes decreased gradually with x values. The nonstoichiometric chemical formulas determined by indirect iodometry showed that with increase of x values the amounts of Fe4+ and oxygen were increased simultaneously. Conductivity measurements exhibited that the increase of Fe4+ mole ratio had a direct influence on the increase of conductivity values and above 673 K each sample showed a transition to pseudometallic conduction.