Physical effects caused by the presence of interfaces between the domains of coexisting ferroelectric and antiferroelectric phases in solid solutions with small difference in free energies of the ferroelectric and antiferroelectric states are discussed in this review. There exist a number of solid solutions in which the two-phase state of domains of the coexisting phases may occur under certain conditions. We present here results of investigations of some effects directly caused by the presence of the interfaces between the domains of the coexisting ferroelectric and antiferroelectric phases. The phenomenological model describing the inhomogeneous state of coexisting domains of the ferroelectric and antiferroelectric phases is presented. Experimental studies of such inhomogeneous state are discussed using two systems of the PbZr1-yTiyO3-based solid solutions. Detailed discussion of the process of local decomposition of solid solutions in the vicinity of ferroelectric-antiferroelectric interphase boundaries and formation of the mesoscopic system of segregates in the vicinity of these interphase boundaries and corresponding experimental results are presented. Results on influence of the system of segregates on dielectric and piezoelectric properties, and also on a dielectric relaxation are presented and discussed. The effects caused by the application of a DC electric field are considered and corresponding experimental results are presented. The experimental results demonstrating the possibility of control of piezoelectric parameters by an external electric field in materials with the antiferroelectric to ferroelectric phase transition via the intermediate state of the coexisting domains of these phases are given.

Department of Chemistry, University of Patras, GR-26500 Patras, GreeceSamples of conducting nanocomposites of polyaniline (PANI) and polypyrrole (PPy) with zeoliteconcentrations from 0 to 50% w/w and ZnO from 0 to 40% w/w were synthesized through oxida-tive polymerization. Their d.c. conductivity was measured under He atmosphere from 80 to 350 Kand their thermal stability was studied by heating them at 70 C for times from 0 to 600 h underenvironmental conditions. The experimental results are consistent with a granular metal structurein which conductive grains are embedded in an insulating matrix and thermal degradation is dueto the corrosion–like shrinking of them with thermal treatment. In the PANI/zeolite composites theconductivity and the thermal stability remain practically unchanged with increasing zeolite content.On the contrary, in PPy/zeolite composites these properties improve with increasing zeolite concen-tration. Moreover, SEM images and XRD patterns of PANI/ZnO composites reveal that a number ofthe ZnO particles are expelled from the matrix, although in PPy/ZnO composites ZnO is completelyencapsulated into the polymer. These differences can be attributed to the stronger bond betweenPANI chains which justify the formation of crystalline conductive grains in it, in contrast to the muchweaker packing of polymer chains in the amorphous PPy.