壓電壓磁橢球顆粒複合材料磁電耦合效應之最佳化

Abstract

磁電耦合效應為材料受到磁場極化時，同時產生電極化現象，反之亦然。磁電耦合效應對於記憶體、磁能轉換器及感測器之應用大有潛力，但自然界中多數單相多鐵性材料之磁電耦合效應都微弱到無法被實際應用，且居禮溫度小於室溫，因此單相多鐵性材料之應用無法普及。因此科學家致力於發展以雙相與多相為主的多鐵性複合材料，其磁電耦合效應不僅優於單相多鐵性材料，同時可於室溫下作用。 本文使用之壓電材料為鈦酸鋇(BaTiO3, BTO)，壓磁材料為鈷鐵氧(CoFe2O4, CFO)。利用Mori-Tanaka微觀力學模型預測橢球顆粒複合材料之磁電耦合效應，藉由改變內含物體積百分比、母材與內含物之極化方向，及內含物之長軸方向，探討三者對於磁電電壓係數之影響，並藉由COMSOL Multiphysics有限元素軟體驗證其結果。 研究結果顯示，橢球顆粒複合材料於固定橢球內含物之長軸方向後，改變母材與內含物之極化方向，可使BTO/CFO配置之最佳磁電電壓係數alpha11由 -0.5294 V/cmOe增加至-1.3651 V/cmOe，alpha33由-0.0303V/cmOe增加至-2.262 V/cmOe (最佳磁電電壓係數提升4.27倍)；CFO/BTO的配置之最佳磁電電壓係數alpha11由-0.7057 V/cmOe增加至-1.836 V/cmOe，alpha33由0.971 V/cmOe增加至-2.876 V/cmOe (最佳磁電電壓係數提升2.96倍)。

Magnetoelectricity (ME) refers to the polarization induced by an external applied magnetic field, or the magnetization induced by an external applied electric field. ME materials are potentially applicable for four-state memory cells, sensors, actuators, and transducers. However, the ME effect in a single phase multiferroic material is weak and is at low temperature. Therefore, scientists resort to composite materials made of piezoelectric and piezomagnetic phases. In this work, we optimize the effective ME voltage coefficient of piezoelectric- piezomagnetic ellipsoidal particulate composites. The optimization of ME effect is with respect to the major axis orientations of ellipsoidal inclusions, the crystallographic orientations, and the volume fraction. We use a micromechanical model, Mori-Tanaka’s method, and the Euler angle transformation to investigate the effective properties of the composites. Following we compare the theoretical results with those predicted by finite element analysis (COMSOL Multiphysics). Numerical results show that they are in good agreement. We show that the effective ME voltage coefficient (alpha11 and alpha33) can be enhanced many-fold at optimal orientation compared to those at normal orientation. For example, the ME voltage coefficient at the optimal orientation is 4.27 times larger than at the normal orientation of BaTiO3 ellipsoidal particulates in a CoFe2O4 matrix. The ME voltage coefficient at the optimal orientation is 2.96 times larger than at the normal orientation of CoFe2O4 ellipsoidal particulates in a BaTiO3 matrix.