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 g3j∗ 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 gh∗, squared figure of merit dh∗gh∗ and electromechanical coupling factor kh∗ of the composite, and large values of gh∗∼102 mV·m/N, dh∗gh∗∼ (10−11-10−10) Pa−1 and kh∗≈ 0.6-0.7 are achieved. A link between max kh∗ 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.