EFFECTS OF GRAIN SHAPE ANISOTROPY, POROSITY, AND MICROCRACKS ON THE ELASTIC AND DIELECTRIC-CONSTANTS OF POLYCRYSTALLINE PIEZOELECTRIC CERAMICS

A theoretical approach is proposed to estimate the effects of grain shape anisotropy on the overall response of polycrystalline piezoelectric ceramics. The self-consistent approach is applicable to a polycrystal with arbitrary grain shapes, orientations, and anisotropy, but emphasis is placed on the effective bulk and shear moduli and the dielectric constant of a polycrystal consisting of randomly oriented piezoelectric grains. Because typical piezoelectric ceramics often contain substantial porosity, the effects of randomly oriented pores of various shapes on the overall electroelastic properties are considered. Analytical predictions are compared to simplified predictions which ignore the effects of piezoelectricity at the grain level and the effects of grain shape. Analytical predictions are in good agreement with measurements for unpoled, porous BaTiO3 polycrystals. A FORTRAN computer program developed to implement the theory is available upon request from the author. (C) 1995 American Institute of Physics.