Effect of Non-Stoichiometry in Ni-Ferrites on Electrical Conduction

Abstract

Five single crystals with nearly same composition but different vacancy concentration between -0.005 and +0.035 in formular unit are grown by the Bridgman method. Resistivity in the frequency range between 100 Hz and 100 MHz and Seebeck coefficient are measured in temperatures ranging from 78 to 300 K. The electrically obtained concentration of Fe 2+ ions is in good agreement with that obtained by chemical analysis. The activation energy of an electron bound to a Fe 2+ ion on B sites is of the order of 10 -2 eV and increases with increasing vacancy concentration. The polaron binding energy is of the same order as the electron binding energy, and corresponds to that of small-polaron conductors. This energy is independent of cation vacancy concentration between 4.7×10 20 and 11×10 20 per unit volume but decreases 13% with the formation of anion vacancy concentration of 1.1×10 20 .