About anomalous properties of porous piezoceramic materials with metalized or rigid surfaces of pores

Abstract

The electromechanical properties of piezoelectric materials can be modified for some specific applications, e.g., hydrophone sensing applications, by incorporating a controlled porosity into them. This work investigates the effective moduli of a newly developed piezoelectric composite, fabricated using a novel approach, in which micro-and nanoparticles of specific metals or stiffer polymers were added to pore-forming agents and transported into ceramic matrices. This technique results in a porous piezocomposite with a metalized pore boundary. According to Newnham’s classification, it is a three-phase piezocomposite with connectivity 3–0–0. We considered a simple unit cell model composing of a cube of the piezoceramic material with a compound spherical pore at its center. The compound pore consists of a spherical vacuum pore and a spherical layer on its boundary. The spherical layer models the material deposited at the interface between the piezoceramic matrix and the pore. Based on the characteristics of this spherical layer, we studied porous piezocomposite with mechanically weak electrically conductive, mechanically hard dielectric, and mechanically hard electrically conductive pore surface. We assumed that this spherical layer is filled with a piezoelectric material. Very high dielectric permittivity moduli simulate the electrical conductivity, very high elastic stiffness moduli modulate the mechanical rigidity, while the piezoelectric moduli are negligible. We developed specific algorithms in ANSYS APDL to calculate the effective moduli of different composites understudy using the finite element method and the theory of effective moduli, considering the Hill–Mandel principle for energy conservation, under certain essential boundary conditions. Our simple unit cell model used for the main calculations was analogous to the model of the corresponding periodic composite. The findings of this basic model were also compared to a more complicated 3–0 random porosity composite model. We confirmed that the effective moduli versus porosity trends in both models are similar. We verified the numerical expectations by studying analytically the homogenization problem of an isotropic dielectric composite. The findings of this work confirm that the effective moduli of the developed piezocomposites significantly depend on the characteristics of material deposited between the piezoceramic and pore phases. The results of this study suggest that there may be several functional applications for these new piezocomposites.