Twelve modified figures of merit of 2–2-type composites based on relaxor-ferroelectric single crystals

Abstract

Twelve modified figures of merit are studied for the first time for 2–2-type composites based on relaxor-ferroelectric single crystals such as [001]-poled (1 – x)Pb(A1/3Nb2/3)O3 – xPbTiO3, where A = Mg or Zn. These modified figures of merit are related to the piezoelectric coefficients d3j* of the composite (j = 1, 2 and 3) and characterise the effectiveness of energy harvesting and transduction along the three co-ordinate axes OXj of a piezoelectric composite under a constant mechanical stress or strain. The volume-fraction dependencies of the modified figures of merit are analysed for parallel-connected 2–2 and 2–2–0 composites, and the effect of porosity (i.e. the volume fraction and shape of air pores in each polymer layer) on these figures of merit is considered for 2–2–0 composites. Linkages between the modified figures of merit and traditional energy-harvesting figures of merit d3j*g3j* are discussed for the studied 2–2-type composites. New diagrams are developed to indicate important volume-fraction ranges that correspond to a large anisotropy of exemplar modified figures of merit. Due to the large effective parameters and large anisotropy of specific figures of merit, the studied composites are of interest in piezoelectric sensor, transducer and energy-harvesting applications.