Highly Anisotropic 1–3–0 Composites Based on Ferroelectric Ceramics: Microgeometry – Volume-Fraction Relations

Abstract

A 1–3-type ferroelectric ceramic / porous polymer composite is studied to show trends in increasing an anisotropy of piezoelectric coefficients d*33/d*31, electromechanical coupling factors k*33/k*31 and k* t /k* p , a ratio of coefficients of electromechanical transformation N*33/N*31, and a ratio of specific acoustic powers of a piezoelectric element. Effects of the porosity and microgeometry of the porous polymer matrix on volume-fraction behaviour of the effective parameters and anisotropy factors in the composite with 1–3–0 connectivity are first analysed in the context of the elastic anisotropy of the matrix. Five conditions are introduced to describe the large anisotropy of the piezoelectric properties and related parameters. Examples of simultaneous validity of the five conditions put forward are discussed to emphasise advantages of the 1–3–0 composite based on the Pb(Zr, Ti)O3-type ceramic over the related 1–3 composite and conventional ferroelectric ceramics. The d*33/d*31 ratio plays the key role in the formulated conditions over the wide volume-fraction range of the ceramic component and at varying the aspect ratio of the air pores and porosity in the matrix. A correlation between the elastic anisotropy of the porous matrix and minima of three anisotropy factors (k*33/k*31, k* t /k* p and N*33/N*31) is first revealed and discussed.