Two orientation effects and large anisotropy of parameters in piezo-active 2–1–2 composites based on [0 1 1]-poled crystals

Abstract

Abstract The results of a comparative study on piezo-active 2–1–2 composites with two ferroelectric components are discussed. The composite structure combines elements of 2–2 (laminar) and 1–3 (fibrous) connectivity patterns. The first component in each composite is domain-engineered [0 1 1]-poled single crystal with macroscopic mm2 symmetry and high piezoelectric activity. The second component is a poled ferroelectric ceramic that is represented by parallel rods in the shape of an elliptic cylinder with a large ratio of semi-axes at its base. The first orientation effect is appreciable due to rotations of the main crystallographic axes X and Y around Z || OX 3 by an angle α in each crystal layer. Rotation of the ceramic rod bases by an angle γ in a polymer medium leads to the second orientation effect in the 2–1–2 composite. The two orientation effects contribute to a large anisotropy of electromechanical coupling factors k 3 j ∗ , energy-harvesting figures of merit (FOM)   ( Q 3 j ∗ ) 2 and modified FOM F 3 j ∗ σ for a stress-driven harvester. The large level of   ( Q 32 ∗ ) 2 , ( Q 33 ∗ ) 2 , F 32 ∗ σ and F 33 ∗ σ (these parameters are of the order of 10−11–10−10 Pa−1) indicates that the studied composites are suitable for piezoelectric sensors, transducers and energy-harvesting systems. New m—α diagrams put forward in the present study show regions wherein the large anisotropy of the effective parameters ( | k 33 ∗ / k 3 f ∗ | ⩾ 5 , ( Q 33 ∗ / Q 3 f ∗ )2 ⩾ 10   and F 33 ∗ σ / F 3 f ∗ σ ⩾ 10 , f = 1 and 2) is achieved when changing the volume fraction m of the single crystal and the rotation angle α. As a result, the leading role of the first orientation effect is emphasised.