| Summary: | 碩士 === 國立聯合大學 === 機械工程學系碩士班 === 108 === In this study, the highly reproducible barium titanate films were prepared from the pure titanium substrates (Ti 99.995%) by plasma electrolytic oxidation (PEO). Using 0.3M barium acetate (Ba(CH3COO)2) and 2M sodium hydroxide (NaOH) as the electrolyte, the temperature of the solution was controlled at 50°C, and the PEO reaction was carried out at a control voltage with a DC power source to produce the barium titanate films having a diameter of 45mm and a thickness of 18μm. The main crystalline phase was cubic, but the tetragonal structure had better material properties, such as ferroelectricity, spontaneous polarization, dielectric constant, etc. Therefore, by subsequent annealing heat treatment, it was desirable to make the crystal phase tend to be tetragonal.
The barium titanate films were annealed in an electric furnace at a constant temperature of 200°C/6hrs, 400°C/6hrs, 600°C/6hrs, 600°C/4hrs, 600°C/2hrs, and then cooled to room temperature. Compared with the unannealed, the barium titanate films with a more white appearance were obtained. Subsequent measured the properties of the specimen under different conditions. The thickness of the film increased slightly as the annealed temperature was higher or the time was longer. The surface roughness results showed that it decreased slightly after heat treatment. The Vickers hardness measurement showed that the hardness increased with the higher heat treatment temperature. The best result was heat treatment of 600°C/6hrs, hardness up to HV 349, the value was close to the Vickers hardness of tetragonal barium titanate. Dielectric constant measurement results showed that it was mainly affected by heat treatment temperature, the best result was heat treatment 600°C/6hrs, the dielectric constant measured at a frequency of 20Hz was 1776. Raman Spectrometer analysis showed that the higher heat treatment temperature and enough heat treatment time it tended to be tetragonal structure, the best result was heat treatment 600°C/6hrs. The material composition was investigated by X-ray diffractometer (XRD). The results showed that the higher heat treatment temperature, the more consistent with the characteristic peak of tetragonal barium titanate. The surface appearance was observed by scanning electron microscope (SEM), and it was found that as the heat treatment temperature was higher, the surface of the film layer became flatter and the pores of the film layer became smaller.
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