Anisotropy Factors and Electromechanical Coupling in Lead-Free 1–3-Type Composites

The effective electromechanical properties and anisotropy factors of novel lead-free 1-3-type composites are studied to demonstrate their large piezoelectric anisotropy and considerable level of electromechanical coupling. The composites studied contain two single-crystal (SC) components and a polymer component. The first piezoactive component is a domain-engineered [001]-poled SC based on ferroelectric alkali niobates-tantalates, and this component is in the form of a system of long rods that are parallel to the poling axis O X
₃
. The second SC component is a system of spheroidal piezoelectric Li
₂
B
₄
O
₇
inclusions aligned in a continuous and relatively large polymer matrix. The SC rods are surrounded by an SC/polymer matrix, and the connectivity of the composite is 1-0-3. It is shown that the conditions d*
₃₃
/|d*
₃₁
| ≥ 5, which indicates a large degree of anisotropy of the piezoelectric coefficients, and k*
₃₃
/|k*
₃₁
| ≥ 5 and k*
_t
/|k*
_p
| ≥ 5, which indicate a large anisotropy of the electromechanical coupling factors (ECFs), can be achieved simultaneously in specific ranges of the component volume fractions and inclusion aspect ratios. Moreover, in the same volume-fraction and aspect-ratio ranges, large ECFs (k*
₃₃
≈ k*
_t
≈ 0.8-0.9) are also achieved. In this context, the important role of the elastic properties of the continuous anisotropic matrix is discussed. The properties and anisotropy factors of the leadfree 1-3-type composites are compared to the similar parameters of conventional lead-containing piezoelectric materials, and the advantages of the composite system studied are described.