Strain behavior study of BNT-based lead-free piezoceramics

• Main Authors: Jaw-yeu Liang, 梁兆宇
• Other Authors: Chen Chia Chou
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/q5nx7k

碩士 === 國立臺灣科技大學 === 機械工程系 === 99 === Giant strain BNT-based solid solution material has been extensively studied recently. However, the origin of formation of large stain is still diverse. Zhang et al. believe that the very large strain is attributed to the structural phase transition between anti-ferroelectric and ferroelectric. However, Teranishi et al. suggested that the very large strain is due to 90°-domain switching in the tetragonal phase observed by the x-ray diffraction under a high electric field. In this case, lead-free piezo-ceramics BNT-xBT (x=3、6、9) were synthesized by a conventional ceramic fabrication process, and we investigated the connection between phase transformation and giant strain properties by observing crystal structures, dielectric properties, field-induced strain properties. Results show the necking phenomenon of (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNB6T) due to lower the depolarization point by adding 6mol% Ba2+. Further, results also show that BNB6T processes wide application temperature range, and exhibits a low temperature dependent strain properties. Besides, we suggest Pmax is one of important consideration for estimating a material whether with giant strain by comparison of the strain properties of BNB3T, BNB6T and BNB9T. On the other hand, we try to substitute 2mol% Ti4+ to adjust ferroelectric properties. The XRD data of BNB6T with 2mol% B-site doping exhibit no peak shifting but the electric properties show different ferroelectric behavior. However, the P-E curve exhibit ferroelectric or antiferroelectric properties with similar structure, indicating the necking behavior of the P-E curve could be attributed to depolarization point shifting and bounding characteristics. We observe that A-site and B-site dopants show different influences on electric properties. Using A-site doping, crystal structure of BNB6T ceramics were modified because of the large ionic radiation of Ba2+. On the other hand, B-site doping may alter the defect states of ferroelectrics. A-site and B-site doping may contribute to a reversible domain switching and good for maintaining the field-induced strain behavior.