AGGREGATE LINEAR PROPERTIES OF FERROELECTRIC CERAMICS AND POLYCRYSTALLINE THIN-FILMS - CALCULATION BY THE METHOD OF EFFECTIVE PIEZOELECTRICMEDIUM

The effective dielectric, piezoelectric, and elastic constants of poly crystalline ferroelectric materials are calculated from single-crystal data by an advanced method of effective medium, which takes into acco unt the piezoelectric interactions between grains in full measure. For bulk BaTiO3 and PbTiO3 polarized ceramics, the dependences of materia l constants on the remanent polarization are reported. Dielectric and elastic constants are computed also for unpolarized c- and a-textured ferroelectric thin films deposited on cubic or amorphous substrates. I t is found that the dielectric properties of BaTiO3 and PbTiO3 polycry stalline thin films strongly depend on the type of crystal texture. Th e influence of two-dimensional clamping by the substrate on the dielec tric and piezoelectric responses of polarized films is described quant itatively and shown to be especially important for the piezoelectric c harge coefficient of BaTiO3 films. (C) 1998 American Institute of Phys ics. [S0021-8979(98)01815-5].