Structure-dielectric properties relations in (Bi0.5Na0.5)TiO3-based lead-free piezoelectric ceramics
| Autor: | Wei-Chih Lee, 李瑋志 |
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| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Lead-based Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics with perovskite structure are widely used as actuators, sensors and micro-electro-mechanical devices owing to their superior dielectric properties. However, toxic lead oxide may evaporate during the heating process due to their high vapor pressure which is risky to human health. Therefore, to develop new environment-friendly materials to replace PZT-based materials has become one of the most attractive topics. In this study, (Bi0.5Na0.5)TiO3 (BNT) lead-free solid solution system was choosen as studied material to investigate the extrinsic and intrincis factors on dielectric/piezoelectric/ferroelectric properties and find out the relation between crystal structure-microstructure-dielectric properties. For extrinsic factor, this study focuses on the microstructure-dielectric properties relation via fabricating dense ceramics with different grain size. The averge grain size of dense ceramics is from 0.28 to 1.81 um. The results show that their dielectric properties performance goes down while grain size decreases, and that is due to their domain switching ability decreases as grain size decreases. This phenomenon significantly affects its properties while the grain size of ceramic is below 0.8 um. For intrinsic factors, this study focuses on establishing the crystal structure-dielectric properties relation. There are three main results. First, the displacement of ions and lattice constant can be calculated via Rietveld method. According to the results, we find the phase transformation is caused from the increase in the distance between cations and anions (dc-a) and the variation in ferroelectric properties is related to dc-a, lattice constant, and the fraction of composed phases. Second, the relation between MPB (Morphotropic Phase Boundary) composition and tolerance factor has been found in this study and two material systems were designed to prove it. Third, by comparing some different MPB compositions, the variation in dielectric/piezoelectric constant is found to proportional to cell volume. Finally, a comprehensive discussion between crystal structure, microstructure, and dielectric/ piezoelectric/ferroelectric properties was made in this study to find out some evidences for developing new lead-free dielectric/ piezoelectric/ferroelectric ceramics. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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