The effective electromechanical properties andanisotropy factors of novel lead-free 1–3-type compositesare studied to demonstrate their large piezoelectricanisotropy and considerable level of electromechanicalcoupling. The composites studied contain two single-crystal components and a polymer component. The firstpiezo-active component is a domain-engineered [001]-poled single crystal based on ferroelectric alkali niobates-tantalates, and this component is in the form of a system oflong rods that are parallel to the poling axis OX3. Thesecond single-crystal component is a system of spheroidalpiezoelectric Li2B4O7 inclusions aligned in a continuousand relatively large polymer matrix. The single-crystalrods are surrounded by a single crystal / polymer matrix,and the connectivity of the composite is 1–0–3. It is shownthat the conditions d * /| d * | 3 5, which indicates a large 33 31degree of anisotropy of the piezoelectric coefficients, and k* /|k* |35and k*/|k*|35,whichindicatealargeanisotropyof the electromechanical coupling factors, can be achievedsimultaneously in specific ranges of the component volumefractions and inclusion aspect ratios. Moreover, in thesame volume-fraction and aspect-ratio ranges, largeelectromechanical coupling factors (k* » k* » 0.8–0.9) are 33 talso achieved. In this context, the important role of the elastic properties of the continuous anisotropic matrix is discussed. The properties and anisotropy factors of the lead-free 1–3-type composites are compared to similar parameters of conventional lead-containing piezoelectric materials, and the advantages of the composite system studied are described.
Preparation and Characterization of Lead-Free Piezoelectric Ceramics