A theory of magnetoelectric coupling with interface effects and aspect-ratio dependence in piezoelectric-piezomagnetic composites

摘要

In a piezoelectric-piezomagnetic composite, one of the most intriguing features of its characteristics is the presence of magnetoelectric coupling coefficient even though neither phase possesses such a property. This quantity is often considered to be the figure of merits, but its magnitude depends on the phase properties, connectivity, volume concentration, inclusion shape, and interfa-cial conditions. In this article, we develop a composite model with aligned spheroidal inclusions in the matrix to account for all these microstructural features. With a focus on the BaTiO_3-CoFe_2O_4 (BTO-CFO) system, we demonstrate how its coupling coefficients, α_(33) and α_(11), and voltage coefficients, α_(E33) and α_(E11), depend on these factors. In particular, we show that a weak interface could significantly lower the coupling effect, 1-3 composites tend to deliver a stronger α_(33) while 2-2 composites a stronger α_(11), and that CFO-in-BTO composites provide stronger coupling than BTO-in-CFO. We conclude by demonstrating that consideration of a weak interface is often essential to model a real system, and that experimentally measured α_(E33) f°r CFO-in-BTO falls below the ideal value of perfect interface but can be predicted by a weak interface model. For ready applications, explicit expressions of α_(33) and α_(11) of fibrous composites and multilayers are also given for both perfect and imperfect interface conditions.