Non-monotonic concentration dependence of electromechanical properties of piezoactive 2-2 composites

The paper reviews the experimental and theoretical non-monotonic dependences of electromechanical properties on the volume concentration of one of the components in two-component piezoactive 2-2 composites. Specific attention is focused on the evolution of piezoelectric coefficients e(ij)* and d(ij)*, their anisotropy and electromechanical coupling factors k(ij)*, k(p)* and k(t)*. This evolution is analysed in terms of the ratios between some electromechanical constants of the components. Important results are concentrated in systems of analytical conditions for reaching max e(31)* > 0 and max k(t)*. These systems are written in terms of introduced 'basic' constants and other parameters depending on the electromechanical properties of the components, and the fulfillment of these conditions is analysed in connection with known experimental data of the components.