On the electrical behavior of nickel ferrite-gallates

The effect of substitution of iron ions by gallium on the AC electrical conduction is studied in the cubic ferrite system NiGaxFe2-xO4 with x varying between (0.0 and 2.0). The variation of conductivity with temperature at different frequencies shows anomalies behavior at T similar to 500 K for all compositions with (0.33 less than or equal to x less than or equal to 2.0). The presence of inflection may reflect unstable oxidation states of the cations over the studied temperature range (300-850 K). The conductivity behavior indicates two different temperature regions; low-temperature region, where the activation energy is constant and polarons may contribute to the conduction mechanism, and high-temperature region, where the activation energy increases with Ga concentration and correlated barrier hopping predominates. (C) 2000 Elsevier Science B.V. All rights reserved.