Lead-Free Multilayer Piezoceramic Composites: Effect of Cosintering on Electromechanical Properties

The macroscopic electromechanical behavior of lead-free multilayer composites was characterized from room temperature to 150 °C. The polar seed component consisted of a nonergodic relaxor (Bi_1/2Na_1/2)TiO₃-7BaTiO₃, with an electric-field-induced long-range ferroelectric order, whereas the nonpolar matrix was an ergodic relaxor Bi_0.5(Na_0.75K_0.25)_0.5 TiO₃-6BiAlO₃ that undergoes a reversible electric-field-induced macroscopic nonpolar-to-polar transition. Microstructural evidence of the effects of cosintering are demonstrated through examination of grain size, interdiffusion, and pore structure. By manipulating the sintering interactions between the two constituents, namely, diffusion paths and residual stresses, both internal mechanical and electrical fields, as well as compositional gradients can be used to enhance the unipolar strain over that expected by a rule of mixtures approximation, thereby improving the properties needed for application of such materials to actuator systems.