| Summary: | 碩士 === 輔仁大學 === 物理學系 === 99 === In-situ high-resolution synchrotron X-ray diffraction reveals a local minimum in rhombohedral distortion angle α_R in the region of 350〜400 oC in BiFeO3, 0.9BiFeO3-0.1BaTiO3, and (Bi0.9Ba0.1)(Fe0.9Ti0.1)O3. The dielectric permittivity exhibits a broad frequency-dependent maximum in the region of 300〜400 oC, which is possibly caused by the antiferromagnetic-paramagnetic transition near the Néel temperature. BiFeO3 proceeds a transition sequence of rhombohedral-orthorhombic-cubic phases near 820 and 850 oC upon heating. A rhombohedral-cubic structure transition takes place near 760 and 720 oC in 0.9BiFeO3-0.1BaTiO3 and (Bi0.9Ba0.1)(Fe0.9Ti0.1)O3, respectively. The dielectric permittivities of 0.9BiFeO3-0.1BaTiO3 and (Bi0.9Ba0.1)(Fe0.9Ti0.1)O3 ceramics are 320 and 120 at room temperature, respectively. The dielectric loss of 0.9BiFeO3-0.1BaTiO3 and (Bi0.9Ba0.1)(Fe0.9Ti0.1)O3 are about 0.04 and 0.02 at room temperature, respectively. This study suggests that the BaTiO3 substitution can enhance dielectric permittivity and also reduce dielectric loss.
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