57Fe Mössbauer and electrical studies of the (NiO)–(Cr2O3)x–(Fe2O3)2−x system

From 57Fe Mössbauer measurements carried out on the spinel ferrite under study, the ratio of the integrated intensities of 57Fe A- and B-site subspectra can be evaluated. The composition of the ferrite has been established as (Fe3+)[Ni2+Cr3+xFe3+1−x] for 0.0 ≤ x ≤ 0.6. The composition dependence of the Mössbauer 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 re-veal a semiconducting behavior with a transition in the conductivity versus temperature curve. The transi-tion temperature is found to decrease linearly with increasing Cr concentration x. The dielectric parameters (ε′and loss (tan δ)) 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.