Iranian Journal of Materials Science and Engineering

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Abstract: Zirconia solid electrolytes with nonequilibrium composite structure were prepared by impregnation of a porous 8YSZ matrix with a solution of Zirconia. Microstructures were characterized by XRD and SEM. The electrical properties were studied by impedance spectroscopy as a function of temperature. Biaxial flexural strength and fracture toughness of composite samples were measured by ring on ring and Vickers microhardness indentation methods respectively. The microstructures of the composite electrolytes were composed of cubic grains surrounded by tetragonal second phase grains. It was shown that the electrical and mechanical properties of the prepared electrolyte can be adjusted by controlling the amount of doped zirconia. Increasing the amount of doped zirconia increases the tetragonal phase content which improves fracture toughness and fracture strength. In addition, increasing tetragonal phase content of the composite electrolytes decreases the conductivity at high temperatures while the situation is reversed at low temperatures.

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In this work, the different fuels (citric acid, glycine and urea) were used for solution combustion synthesis of CoFe₂O₄ powders. X-ray diffraction, Raman spectroscopy, electron microscopy and vibrating sample magnetometry techniques were employed for characterization of phase evolution, cation distribution, microstructure and magnetic properties of the as-combusted CoFe₂O₄ powders. Single phase CoFe₂O₄ powders with partially inverse structure in which the Co²⁺ cations are distributed in both tetrahedral and octahedral sites were synthesized by the citric acid, glycine and urea fuels. The as-combusted CoFe₂O₄ powders by the citric acid fuel exhibited the highest inversion coefficient. The crystallite size of the as-combusted CoFe₂O₄ powders synthesized by urea fuel was 15 nm, increased to 41 and 52 nm for the glycine and citric acid fuels, respectively. Furthermore, the solution combusted CoFe₂O₄ powders showed ferromagnetic behavior with saturation magnetization of 61.9, 63.6 and 41.6 emu/g for the citric acid, glycine and urea fuels, respectively. The high crystallinity and particle size of the as-combusted CoFe₂O₄ powders using glycine fuel led to the highest magnetization and the moderate coercivity.