Lead-free 0–3-type composites: From piezoelectric sensitivity to modified figures of merit

Effective piezoelectric properties, electromechanical coupling factors (ECF) and figures of merit (FOM) are studied in lead-free 0–3-type composites based on novel ferroelectric 0.965( K 0 . 4 8 Na 0 . 5 2 ) ( Nb 0 . 9 6 Sb 0 . 0 4 ) O3–0.035 Bi 0 . 5 Na 0 . 5 Zr 0 . 1 5 Hf 0 . 7 5 O3 ceramic. Systems of prolate ceramic inclusions are surrounded by a large polymer matrix that can be either monolithic (in the 0–3 composite) or porous (in the 0–3–0 composite). Non-monotonic volume-fraction dependences of the effective piezoelectric coefficients g 3 j ∗ , ECF k 3 j ∗ , squared FOM d 3 j ∗ g 3 j ∗ and their modified analogs for stress-driven systems are analysed, and examples of the high longitudinal piezoelectric sensitivity ( g 3 3 ∗ > 100 mV ⋅m/N) are considered. A role of microgeometrical factors, that promote the large effective parameters and anisotropy of properties in the 0–3-type composites, is highlighted. New “aspect ratio — volume fraction” diagrams are first built to describe conditions for high piezoelectric sensitivity, large modified FOM and their anisotropy in the studied composites. These advanced materials can be of value for piezoelectric sensor, energy-harvesting and related applications.