壓電壓磁顆粒複合材料磁電耦合效應之最佳化

Abstract

磁電耦合效應是電場與磁場之間藉由應變相互轉換的現象，在記憶體、感測器應用上有相當大的潛力。由於單相多鐵性材料的磁電耦合效應太微弱而不足以應用，所以發展出雙相或多相多鐵性複合材料，藉此來提升磁電耦合效應。然而壓電與壓磁材料為非等向性材料，因此改變極化方向能進一步提升磁電耦合效應。 本研究使用之壓電材料為鈮酸鋰 (LiNbO3,LNO)與鈦酸鋇(BaTiO3,BTO)，壓磁材料為鈷鐵氧(CoFe2O4,CFO)，利用Mori-Tanaka微觀力學模型與尤拉角來尋找最佳磁電耦合效應之體積比與極化方向，最後運用COMSOL Multiphysics有限元素軟體驗證結果。研究結果顯示，經過極化方向與磁軸方向的轉換後，LNO[001]/CFO[001]之最佳αE,11*提升約1.19倍；CFO[001]/LNO[001]之最佳αE,11*提升約1.27倍。若將壓電材料換成BTO，旋轉極化方向之結果發現磁電電壓係數皆沒有提升。更進一步我們發現，壓電材料之壓電係數中，e15對磁電電壓係數αE,11*之影響最大，且LNO-CFO與BTO-CFO之最佳極化方向相當靠近LNO與BTO壓電係數e15之最佳極化方向。

Magnetoelectricity (ME) effect refers to the coupling between electric and magnetic fields. These make them particularly appealing and promising for a wide range of applications, such as four-state memory cells and large area sensitive detection of magnetic fields. However, the ME effect in single-phase materials is rather weak or cannot be observed at room temperature. Composite materials made of piezoelectric and piezomagnetic phases, on the other hand, offer an alternative option for the improvement of ME coupling. This work studies the magnetoelectricity of a spherical particulate composite made of piezoelectric and piezomagnetic phases. The ME effect of crystallographic orientation and volume fraction is investegated by the Mori-Tanaka micromechnical approach. The result are in good agreement with those predicted by finite element analysis. Based on this micromechanical method, we show that the effective ME voltage coefficient can be enhanced many-fold at the optimal orientation compared to those at normal cut. For example, the ME voltage coefficient at the optimal orientation is 1.19 times larger than that at the normal orientation of "LiNb" "O" _"3" particulates in a CoFe24 matrix, while the optimal coupling coefficient is 1.27 times larger than that at the normal cut of CoFe2O4 particulates in a LiNbO3 matrix. In addition, the normal orientation is the best of BaTiO3-CoFe2O4 composites. Finally, we obverve that the ME voltage coefficient is sensitive to the piezoelectric constant e15. The optimal orientation of ME voltage coefficient is near that of the piezoelectric constant e15.