Novel high-performance 2–1–2 composites with two ferroelectric components causing a variable anisotropy of figures of merit

Abstract

A high performance of novel three-component composites with 2–1–2 connectivity is reported and discussed. Layers of the composites are parallel-connected, and each layer contains the ferroelectric (FE) component. The layer of the first type (LFT) represents domain-engineered single crystal poled along either [0 0 1] or [0 1 1]. The layer of the second type is described as a system of long FE ceramic rods that have the shape of an elliptic cylinder and are aligned in a polymer medium. Piezoelectric coefficients d 3*j and g *3j and sets of figures of merit (FOM) (energy-harvesting d 3*jg *3j, modified F 3*j for a stress-driven harvester and modified F 3*j for a strain-driven harvester) are analyzed to show their large values and specifics of the anisotropy when varying volume fractions of components and a rotation angle of the ceramic rod bases. For the first time, the studied parameters are compared in two directions: (i) the composite based on [0 0 1]-poled single crystal versus the composite based on [0 1 1]-poled single crystal and (ii) the lead-free composite versus the lead-containing composite (both based on [0 0 1]-poled single crystals). The advantages of the high-performance lead-free composite are discussed. The 2–1–2 composites put forward in this paper are of interest as advanced materials suitable for piezoelectric sensors, actuators and energy-harvesting systems operating at constant stress or strain.