On the time variation of the electrical conductivity in some spinel magnetic ceramics

In a previous paper we have reported on the time modification of the electrical conductivity σ of freshly prepared and quenched polycrystals of various spinel ferrites, observed at room temperature and above. We found that for some ferrites σ decreases whereas for others it increases, immediately after sintering. We assumed that this time effect (named by us “electric relaxation”) can be explained by the probable changes in cation distribution between tetrahedral (A) and octahedral (B) sites of the spinel lattice which take place after rapidly cooling samples to reach the equilibrium distribution. The aim of the present paper is to report on the measurements of the time variation of the electrical conductivity on various polycrystalline ferrites to elucidate the complexity of the phenomenon