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M.N.V. Ramesh and K.V. Ramesh

Abstract

Zr substituted 0.8BaTiO30.2 Bi0.5K0.5TiO3 lead free ceramic materials with a composition 0.8Ba0.2(Bi0.5K0.5)Ti1-xZrxO3 (0.01 ≤ x ≤ 0.06) were prepared by conventional solid state reaction method followed by high energy ball milling. The X-ray diffraction studies confirmed the tetragonal structure of the material at room temperature. Density was decreasing with the substitution of Zr. Microstructure studies were done by using scanning electron microscope. Temperature and frequency dependent dielectric studies were carried out and showed that the dielectric constant, dielectric loss and Curie temperature were decreasing with the substitution of Zr. Relaxor behavior was observed in all the Zr substituted samples. Degree of diffuseness was calculated from the modified Curie-Weiss law and it was found to increase with the substitution of Zr. Frequency and temperature dependent AC conductivity was calculated and it was found to obey Jonscher’s power law. Substitution of Zr decreased the conductivity of the material. Activation energy was calculated and it was decreasing with an increase in Zr substitution.

Open access

B.B.V.S. Vara Prasad, K.V. Ramesh and A. Srinivas

Abstract

Co–Zn nanocrystalline ferrites with chemical composition Co0:5Zn0:5Fe2O4 were synthesized by sol-gel and combustion methods. The sol-gel method was carried out in two ways, i.e. based on chelating agents PVA and PEG of high and low molecular weights. In auto-combustion method, the ratio of citric acid to metal nitrate was taken as 1:1, while in sol-gel method the chelating agents were taken based on oxygen balance. All the three samples were studied by thermogravimetric and differential thermal analysis for the identification of phase formation and ferritization temperature. The synthesized samples were characterized by powder X-ray diffraction and FT-IR spectroscopy without any thermal treatment. The measured lattice constants and observed characteristic IR absorption bands of the three samples are in good agreement with the reported values showing the formation of a cubic spinel structure. The crystallite sizes of all samples were determined using high intensity peaks and W-H plot. Size-Strain Plot method was also implemented since two of the samples showed low crystallite sizes. The least crystallite size (5.5 nm) was observed for the sample CZVP while the highest (23.8 nm) was observed for the sample CZCA. Cation distribution was proposed based on calculated and observed intensity ratios of selected planes from X ray diffraction data. All structural parameters were presented using experimental lattice constant and oxygen positional parameter, and they correlated with FT-IR results. Magnetic measurements were carried out using vibrating sample magnetometer at room temperature to obtain the characteristic parameters such as saturation magnetization, coercivity, remanence, squareness ratio and Bohr magnetons. Among all, the sample synthesized via citric acid autocombustion method displayed a remarkably higher magnetization of 53 emu/g and the remaining two samples displayed low magnetization values owing to their smaller crystallite sizes.