Electromechanical loading behaviors of barium titanate single crystals in the non-variant (110) direction

本論文主要為探討鈦酸鋇單晶同時受到非變量方向之(110)晶面方向上的壓應力及交互電場時，鈦酸鋇單晶(110)方向之應變量表現情形。 鈦酸鋇單晶(110)方向力電耦合實驗中，常溫下對鈦酸鋇單晶施加±1.25 MV/m之交互電場，當壓應力施加至3.03 MPa時，鈦酸鋇單晶(110)方向之應變量從0.17 %提升至0.2 %；而55 ℃下，當壓應力施加至11.85 MPa時，應變量0.07 %提升至0.19 %。 這表示對鈦酸鋇單晶施加非變量方向之(110)晶面方向壓應力，也能誘使鈦酸鋇單晶中更多的偶極發生out-of-plane方向之90°翻轉，進而提升鈦酸鋇單晶(110)方向之應變量。 為了得到往後模擬所需之模擬參數，我們利用即時影像觀察實驗得到常溫和55 ℃下鈦酸鋇單晶內偶極發生in-plane面上90°晶域翻轉的起始電場和結束電場。 接著利用即時影像觀察實驗和力電耦合實驗所得之數據進行鈦酸鋇單晶(110)方向力電耦合實驗的電滯曲線及蝴蝶曲線模擬，並進一步地比較實驗結果和模擬結果，以判斷鈦酸鋇單晶中偶極的翻轉方式。 從此模擬和實驗結果的比較中，我們可以確認常溫實驗時，偶極受到試片側邊去極化場的影響，使得更多的偶極在翻轉的過程中經過out-of-plane方向。 而55 ℃實驗時，溫度的提升使試片側邊之去極場下降，使得有較少得偶極在翻轉的過程中經過out-of-plane方向，且有部分的偶極以in-plane面上90°翻轉進行翻轉，因此在55 ℃無施加壓應力時得到較小的應變量，且需要更大的壓應力才能得到和常溫類似的最大應變量表現。 最後我們對工業常見的線性元件層狀堆疊致動器施加平行或垂直致動器極化方向之壓應力和極化表現線性範圍之交互電場，同樣觀察平行或垂直致動器極化方向之壓應力對致動器的應變量影響情形。 於實驗中，不管是平行還是垂直致動器極化方向之壓應力皆能略微提升致動器的應變量，且垂直致動器極化方向之側向壓應力效果較平行致動器極化方向之正向壓應力來得好。Strain behavior of barium titanate (BaTiO3) single crystals under combined electrical and mechanical loading in non-variant (110) direction is studied. A maximum strain of 0.2 % is obtained on BaTiO3 single crystals under a compressive stress of 3.03 MPa and a cyclic electric field of ±1.25 MVm-1, both applied in the (110) direction at room temperature. In contrast, when the external electrical and mechanical loading is applied at 55 °C, a maximum strain of 0.19 % is obtained when the compressive stress is increased to 11.85 MPa. This difference is believed to be caused by the variation in the magnitude of depolarization field at two temperatures. This study demonstrates that the enhancement of electrostrain in BaTiO3 single crystals can be achieved by applying a bias-stress even if the loading is in a non-variant direction. To compare with the experimental data, the polarization and stain hystereses of BaTiO3 single crystals with electromechanical loading in the (110) direction at room temperature and 55 °C are simulated using the multirank laminate model. The parameters required for modeling, such as the starting and finishing electrical fields for the in-plane and out-of-plane 90° domain switchings, are obtained from in-situ domain observations using optical microscopy. By examining the experimental and modeling results, it is concluded that for BaTiO3 single crystals loaded in the (110) direction, the magnitude of depolarization field and the extent of in-plane 90° switching are the key factors governing the effectiveness of bias-stress on the enhancement of electrostrain. The strain characteristics of linear PZT stack actuators under combined electrical and mechanical loading are also investigated in this study. It is found that the most effective way to increase the linear strain (i.e., piezoelectric strain) is by applying the bias-stress perpendicular to the electric field. This is caused by the further alignment of electrical dipoles in the electric field direction due to the applied stress