57Fe Mossbauer and electrical studies of the (NiO)-(Cr2O3)x-(Fe2O3)2-x system

From Fe-57 Mossbauer measurements carried out on the spinel ferrite under study, the ratio of the integrated intensities of Fe-57 A- and B-site subspectra can be evaluated. The composition of the ferrite has been established as (Fe3+) [Ni2+Crx3+Fe1-x3+]O-4(2-) for 0.0 less than or equal to x less than or equal to 0.6. The composition dependence of the Mossbauer hyperfine parameters (center shift and quadrupole splitting) displays no features in this composition range that would result from a qualitative change in electronic structure. The ac conductivity measurements reveal a semiconducting behavior with a transition in the conductivity versus temperature curve. The transition temperature is found to decrease linearly with increasing Cr concentration x. The dielectric parameters (epsilon' and loss (tan delta)) of the studied samples exhibit dipolar relaxation effects. The results of conductivity and dielectric parameters are explained in the light of hopping conduction at the octahedral B sites.