Study the effect of sintering temperature on structural, microstructural and electromagnetic properties of 10% Ca-doped Mn0.6Zn0.4Fe2O4

Calcium doped manganese-zinc ferrite having the nominal composition Mn0.6−xCaxZn0.4Fe2O4 (x=0.0, 0.1) were prepared via the conventional solid-state sintering method, which were sintered at 1150, 1200 and 1250 °C for 5 h. The microstructure and surface morphology were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscope (SEM). XRD patterns revealed the formation of pure spinel phase ferrites with α-Fe2O3 impurity phase. FTIR spectra showed two absorption bands (ν1 and ν2) attributed to stretching vibration of tetrahedral and octahedral complex Fe3+-O2−, respectively. SEM micrographs displayed non-homogeneous grains of polyhedral shape but with increased grain size along with the increase of sintering temperature. Pure and calcium doped samples exhibit the highest dielectric constant at 1250 °C. Calcium doped sample has lower dielectric constant as compared to the pristine sample which is attributed to the retardation in electron exchange mechanism caused by lockup among iron and calcium ion. The dielectric loss peaks in pristine sample is attributed to the hopping frequency of Fe2+/Fe3+ between the tetrahedral and octahedral sites nearly equal to the frequency of the applied field. Calcium doped sample exhibits improved AC conductivity compare to the undoped sample at 1200 °C and 1250 °C because the electron hopping between Fe3+ and Fe2+ increases as the migration of Fe3+ to the B-sites increases with the occupancy of Ca2+ in the A-sites. Complex impedance spectra revealed that the conduction process is mainly attributed due to the processes which are associated with the grain and grain boundary in pristine sample and in calcium doped sample is associated with the grain only at 1150 and 1200 °C. Calcium substituted sample has lower permeability than that of pristine sample because Ca2+ can segregate the grain boundaries and creates an insulating layer as a consequence the domain wall movement and domain rotation become difficult.