Impact of Divalent and Trivalent Cations on the Properties of Sr Based X-Type Hexagonal Nanoferrites.

Abstract

This dissertation is focused on the synthesis and characterizations of SrNi based X-type hexagonal ferrites substituted with divalent and trivalent cations (Cr3+, Bi3+ , Al3+, In3+, Zn2+, Cu2+, Co2+). The dissertation presents systematically five series: Sr2Ni2TxFe28-xO46 (T = Cr3+, Bi3+, Al3+ and In3+; x = 0.0, 0.25), Sr2-xZnxNi2Fe28-yCryO46 (x = 0.00, 0.01, 0.02, 0.03, 0.04; y = 0.0, 0.2, 0.4, 0.6, 0.8), Sr2-xCoxNi2Fe28-yBiyO46 (x = 0.00, 0.01, 0.02, 0.03, 0.04; y = 0.00, 0.05, 0.10, 0.15, 0.20), Sr2-xCuxNi2Fe28-yAlyO46 (x = 0.00, 0.01, 0.02, 0.03, 0.04; y = 0.0, 0.2, 0.4, 0.6, 0.8) and Sr2-xCoxNi2Fe28-yInyO46 (x = 0.00, 0.01, 0.02, 0.03, 0.04; y = 0.00, 0.05, 0.10, 0.15, 0.20) of X-type hexagonal ferrites. These samples are synthesized via sol-gel route, annealed at 1250 oC and characterized by thermal gravimetric analysis (1300 °C), X-ray diffraction analysis, vibrating sample magnetometer technique and dielectric analysis (1MHz to 3GHz). The phase temperature by thermo-gravimetric analysis (TGA), revealed that the X-type hexagonal phase of these materials is highly stable above 1200 oC. Phase of these materials is verified through X-ray diffraction patterns. The crystallite size of all these materials is under 30 nm. Saturation magnetization is found to increase with substitution of Al3+ , Cr3+ -Zn2+ and Bi3+ -Co2+ cations. It decreased with substitution of Cr3+, Bi3+ , In 3+ , Cr3+ -Zn2+, Al3+ -Cu2+ and In3+ -Co2+ cations. Coercivity increased with substitution of Cr3+, Al3+, In3+, In3+ -Co2+ and Cr3+ -Zn2+ cations. It is found to decrease with substitution of Bi3+ and Bi3+ -Co2+ cations. Dielectric constant enhanced with substitution of Al3+, Cr3+ -Zn2+ and In3+ -Co2+ cations at resonance frequency. The higher value of dielectric constant up to 123 is attained for sample iii Sr1.97Zn0.03Ni2Fe27.40Cr0.6O46. The decrement in dielectric constant is observed with substitution of Cr3+, Bi3+, In3+, Bi3+ -Co2+ and Al3+ -Cu2+ cations. Dielectric loss factor reduced with the incorporation of Cr3+, Bi3+, In3+, Bi3+ -Co2+ and Al3+ -Cu2+ cations at resonance frequency. It enhanced with the substitution of Al3+, Cr3+ -Zn2+ and In3+ -Co2+ cations. The sample Sr1.96Ni2Co0.04In0.8Fe27.2 showed very high value of tangent loss of nearly 650 at 2.3 GHz. This dissertation provides all useful explanation of all the processes that undergo as a result of substitution and optimize crystallographic, magnetic as well as dielectric characteristics of Sr based X-type hexagonal ferrites. The results of all prepared materials confirm our aim of fabricating X-type hexagonal materials for EM absorbing and storage applications. The large values of dielectric constant, moderate values of Dielectric loss, large values of saturation magnetization and low coercivity indicate good absorption properties of these materials, which reveal their utilization as electromagnetic absorbers in RAM, stealth, etc. The large values of coercivity along with excellent dielectric constant of some samples reveal potential applications of these materials in storage devices.