| Summary: | 碩士 === 南台科技大學 === 電子工程系 === 97 === In this study, different contents of Li2CO3 and Ta2O5 were doped and substituted into the lead-free K0.5Na0.5NbO3-based (KNN-based) ferroelectric ceramics to form K0.5Na0.5(Nb1-XTaX)O3 and (1-x)K0.5Na0.5NbO3+xLi2CO3 ceramics by the conventional solid-state method, respectively. By the analysis of XRD, SEM, dielectric constant, and relative density, the optimum composition and fabricated parameters will be obtained. From the experimental results, it is evident seen that, the doping of Li2CO3 could increase the Curie temperature (Tc) about 20~50 ℃ to 465 ℃. In addition, from the analysis of the Morphotropic Phase Boundary (MPB), the crystal phase of this KNN-based ceramics were changed from the tetragonal to the cubic structures and its dielectric constants increased obviously as the temperature increased. On the other way, in the KNN-based ceramics, the substitution of Ta2O5 for Nb2O5 would increase the sintering temperature from 1100 ℃ to 1120 ℃, the average grain size was 3 μm, and the relative density of K0.5Na0.5(Nb0.95Ta0.05)O3 ceramics could achieve about 95.6 % of the theorical density (4.51 g/cm3). Finally, in this thesis, all of the dielectric, ferroelectric and sintering characteristics of the Ta-substituted and Li-doped KNN-based ferroelectric ceramics would be investigated in detail.
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