| Summary: | 碩士 === 東海大學 === 化學工程與材料工程學系 === 106 === In this study, (Bi0.9Gd0.1)(Fe1-xCrx)O3 (BGFCO, x = 0, 0.05, 0.1, 0.15, 0.2) multiferroic materials were prepared by sol-gel and solid-state methods. The effects of doping Gd and Cr on the structure, thermal expansion coefficient, microstructure, and magnetic and dielectrical properties have been investigated.
The multiferroic materials were sintered for 16 hours at the temperature of 720-900℃ in the atmospheric environment. The relative densities of multiferroic materials were all above 60%. The XRD result showed that heterogeneous phase was reduced after doping 10 mol% Gd. When the doping amount of Cr increased, the signal of (201) was higher than those of (104) and (110) and became the main diffraction peak. The variations of microstructure were observed by using SEM at magnifications of 200, 3000, and 10000X, respectively. The voids became smaller after doping 10 mol% Gd and the grain shape was elliptical. When the doping amount of Cr increased, the grain shape transferred to square. The coefficients of thermal expansion of the multiferroic materials prepared by the sol-gel method were lower than those prepared by solid-state method at the same composition ratios. The g-(Bi0.9Gd0.1)(Fe0.95Cr0.05)O3 prepared by sol-gel method possessed a minimum coefficient of thermal expansions of 7.29 μm/moC.
By using network analyzer with a resonator frequency of 7 GHz, dielectric properties were measured by microwaves of 7, 8, and 10 GHz, respectively. Magnetic properties were measured by microwaves of 7.5, 9, and 11 GHz, respectively. The g-(Bi0.9Gd0.1)(Fe0.95Cr0.05)O3 and the g-BiFeO3 prepared by sol-gel method possessed a maximum dielectric constant of 7.625 and a minimum dielectric loss of 0.00096 at 7 GHz, respectively. The g-(Bi0.9Gd0.1)(Fe0.95Cr0.05)O3 prepared by sol-gel method and s-(Bi0.9Gd0.1)(Fe0.9Cr0.1)O3 prepared by solid state method possessed a maximum permeability of 28.721 and a minimum magnetic loss of 0.063 at 7.5 GHz, respectively.
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