Please use this identifier to cite or link to this item:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/42385
Title: | 溫度對鈦酸鋇單晶形變之影響 A temperature-dependent study on the strain behaviors of barium titanate single crystals |
Authors: | Jhe-An Lin 林哲安 |
Advisor: | 謝宗霖(Jay Shieh) |
Keyword: | 鈦酸鋇單晶,力電耦合,晶域翻轉,去極化,即時影像觀察,模擬, BaTiO3,Electromechanical loading,Domain switching,Depolarization field,In-situ observation,Multi-rank simulation, |
Publication Year : | 2009 |
Degree: | 碩士 |
Abstract: | 力電耦合可以有效提升鈦酸鋇單晶的應變量。 常溫時,在施加2.74 MPa的應力下,可以得到最大應變量為0.45 %;電滯表現偏離一般鐵電單晶所看到的典型圖形,具有較大的矯頑電場,較小的飽和極化量和殘留極化量,表示在最大電場下,晶域隨電場轉向並不完全,仍存在與電場方向平行但相反的偶極,在電場為零時,應變曲線和電滯曲線具有不對等斜率關係,此不對等關係來自於「成對」偶極發生90°翻轉,使極化量的變化接近於零,應變量卻有明顯下降。
55 ℃時,在施加0.99 MPa的應力下,可以得到最大應變量為0.8 %; 曲線具有軟鐵電特性,與常溫比較,在電場為零時,應變曲線和電滯曲線不對等斜率關係明顯下降,是因溫度增加了晶域壁的移動能力,減少了在最大電場下,未轉向電場方向的晶域,因此,極化量的變化接近於零,應變量卻有明顯下降的現象就不再出現。 即時影像觀察可以發現常溫與55 ℃下,晶域作90°翻轉的機制並不相同。 常溫下,會出現白色類似氣泡狀的亮點,代表微晶域在作90°翻轉,具有類似成核及成長的機制,且大部分晶域幾乎在同一電場下發生翻轉。 55℃下,晶域發生90°翻轉,是藉由90°晶域壁的移動,不需成核的機構,出現晶域壁sweeping的現象。 模擬結果顯示,去極化場會導致晶域作in-plane方向上的180°翻轉,晶域作in-plane方向上的180°翻轉所消耗的能量會影響應變量的大小。 常溫下,即使在大應力下,也無法有效提升應變量。 相對來說,在55℃下,有效降低去極化場效應,使小應力下,即可有效提升應變量。 For actuator applications, it is important to develop large strains in BaTiO3 single crystals under combined electrical and mechanical loadings. At room temperature, a maximum strain of about 0.45 % is obtained on a BaTiO3 single crystal under a compressive stress of 2.74 MPa and a cyclic electric field of ± 1.25MVm-1. The measured hysteresis loop though deviates from the classic shape. It has a lower polarization saturation value and a higher coercive field. These are strong indications that switching is incomplete at maximum electric field for the BaTiO3 single crystal, possibly leaving some domains with 180° relative orientation. A serve disproportion of slope gradients is observed at zero electric field for the measured polarization and strain hysteresis curves. A likely cause for the ‘decoupling’ of switching polarization and switching strain is the cooperative operation of multiple 90° switching systems by which ‘polarization-free’ strain changes are induced. For the same BaTiO3 single crystal, at 55 °C, a maximum strain of about 0.8 % is obtained under a compressive stress of 0.99 MPa and a cyclic electric field of ± 1.25 MVm-1. The measured hysteresis loop displays the classic behavior of a soft-switching ferroelectric single crystal. When compared with the hysteresis measurements at room temperature, the degree of discrepancy between the slope gradients at zero electric field for the polarization and strain hysteresis curves is significantly reduced. This is due to the increase in domain wall mobility with increasing temperature, lowering the extent of incomplete switching at maximum electric field. Hence, the polarization-free straining is no longer available. From the in-situ observations of domain switching, the mechanisms of 90°-domain-switching at room temperature and at 55 °C are found to be different. At room temperature, the observed white bubble-like spots represent the nucleation of 90°domains, and most domains switch at a specific electric field. In contrast, at 55°C, domains switch gradually with increasing electric field, and domain wall sweeping is observed without nucleation. Multi-rank-based simulations show that the in-plane alternating layers of 180° domains are induced by the depolarization field. The magnitudes of dissipation energies when domains perform in-plane switching will affect attainable actuation strains. At room temperature, it is difficult to increase actuating strain even under large stresses. However, at 55 °C, it is relatively easy to increase actuating strain under small stresses due to the decrease of depolarization effect. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/42385 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 材料科學與工程學系 |
Files in This Item:
File | Size | Format | |
---|---|---|---|
ntu-98-1.pdf Restricted Access | 5.5 MB | Adobe PDF |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.