Grain‐Boundary and Grain Electrical Resistances in Co x Fe 3−x O 4

The complex impedance analysis technique was used to separate the grain‐boundary and grain impedances of ferrites of the system Co x Fe 3−x O 4 . All the samples, for x = 0.886, 0.960, 0.980, 0.995, 0.999, 1.005, 1.011, 1.021, 1.041, and 1.126, were fabricated by the traditional routine under the same conditions of preparation and sintering. The variations of both grain‐boundary and grain resistances with temperature were evaluated in the frequency range 100 Hz < f < 40 MHz. The values of the activation energies for both conduction processes were determined from the Arrhenius plots, and the variations of these activation energies and of the resistances at 20° and 150°C were drawn as a function of x. A sharp change in these quantities was observed at the stoichiometric composition (x = 1). Explanations and suggestions for the observed behaviors have been made.