Piezoelectric sensitivity and hydrostatic response of novel lead-free 2–0–2 composites with two single-crystal components

This paper reports the piezoelectric performance and important related hydrostatic parameters of 2–0–2 composites based on lead-free ferroelectric and piezoelectric single crystals with 4mm symmetry. We demonstrate that ferroelectric domain-engineered alkali niobate-tantalate based single crystals provide large values of the piezoelectric coefficients g_3j ^∗ and related parameters when used in a 2–0–2 composite system with a relatively wide range of volume fractions of single-crystal components. An ‘aspect-ratio effect’ as a result of the presence of inclusions of a piezoelectric Li₂B₄O₇ single crystal in a polymer medium is studied for the first time for a case where the elastic compliance s₁₂ in the single crystal/polymer layer of the composite passes through zero. It is observed that changes in the aspect ratio and volume fraction of the Li₂B₄O₇ inclusions influence the hydrostatic piezoelectric coefficient g_h ^∗, squared figure of merit d_h ^∗g_h ^∗ and electromechanical coupling factor k_h ^∗ of the composite, and large values of g_h ^∗∼10² mV·m/N, d_h ^∗g_h ^∗∼ (10⁻¹¹–10⁻¹⁰) Pa⁻¹ and k_h ^∗≈ 0.6–0.7 are achieved. A link between max k_h ^∗ and a change in sgns₁₂ is first described for the 2–2-type composite, and a comparison of the hydrostatic parameters of the novel and related composites is made. The present results show the potential of lead-free 2–0–2 composites that are suitable for piezoelectric sensor, energy-harvesting and hydroacoustic applications.