三相壓電壓磁顆粒複合材料之磁電耦合效應

Abstract

磁電耦合效應擁有電場與磁場兩個物理場之間相互轉換的功能，在記憶體、感測器方面有很大的運用潛力，但在單相材料中的磁電耦合效應微弱，故本文針對三相壓電壓磁複合材料之磁電耦合效應進行研究。其結構為圓球狀內含物外面包覆一層殼層分佈於母材中，藉由不同壓電壓磁材料的相互搭配以及改變材料係數以尋找出最佳的磁電耦合效應。除了利用三相壓電壓磁材料之外，另外在雙相壓電與壓磁材料之間加入功能性漸變材料，預期能夠有效降低界面材料破損的問題以及獲得磁電耦合效應的提升。 本文利用微觀力學模型─Mori-Tanaka模式以及雙層法(Two-level recursive scheme)進行等效性質與磁電耦合效應的模擬；另外亦使用有限元素軟體COMSOL Multiphysics來驗證理論結果。研究成果顯示，在現有常用的材料中，三相複合材料最佳的配置為LiNbO3/CoFe2O4/Terfenol-D，其磁電電壓係數為-38V/cmOe，其磁電耦合效應比起對應的雙相複合材料(LiNbO3/Terfenol-D)最多能提升至4.2倍。此外亦發現，降低材料的介電係數以及母材的彈性係數對於磁電耦合效應有大幅度的提升。並且發現彈性係數與磁電耦合效應具有相關性：在同時擁有兩相壓磁材料的情況下，較高的磁導率以及較低的壓磁係數需搭配較高的彈性係數；較低的磁導率以及較高的壓磁係數則需搭配較低的彈性係數。此外在彈性係數較高的情況下去改變材料的介電係數與磁導率，對於磁電耦合效應影響較顯著。

Magnetoelectric (ME) effects refer to the coupling between magnetic and electric fields, which is potentially applicable for memories and sensors. However, in a single-phase compound, the ME effect is weak. Therefore, we investigates the effective magnetoelectricity of core-shell-matrix three-phase composites made of piezoelectric (PE) and piezomagnetic (PM) materials. We optimize the ME voltage coefficient with respect to the material properties and volume ratio of each constituent. In addition, we insert a functionally graded material between the two-phase PE/PM composite to prevent the interface failure and to enhance the ME effect. We use two micromechanical models, Mori-Tanaka method and the two-level recursive scheme, to investigate the effective properties. Further, we employ finite element analysis (COMSOL Multiphysics) to verify the theoretical results. We show that the ME voltage coefficients can be enhanced many-fold for the three-phase ME composite compared to the corresponding two-phase counterpart. For example, we show that the constants and are -38V/cmOe and -11V/cmOe, respectively, of the three-phase composite LiNbO3/CoFe2O4/Terfenol-D, which are 4.2 and 1.7 times larger for the corresponding two-phase LiNbO3/Terfenol-D media. Further, to enhance the ME effect, we can choose materials with lower dielectric permittivity or the matrix phase with lower elastic constant. For the PE/PM/PM and PM/PE/PM cases, we can improve the coupling effect by choosing one PM phase with higher magnetic permeability, lower piezomagnetic coefficient and higher elastic constant, while the other PM phase with lower magnetic permeability, higher piezomagnetic coefficient and lower elastic constant. Finally, if the materials are with higher elastic constant, the ME voltage coefficient is significantly influenced by the dielectric permittivity and magnetic permeability.