Dielectric properties of ferroelectric powders and microcomposites

Dielectric spectra of microcomposites depend both on volume fractions and internal geometry. They consist of the bulk modes corresponding to the percolated clusters and geometrical modes of finite size clusters at higher frequencies. The ferroelectric-dielectric composite does not exhibit full softening of the soft mode below the percolation threshold of the ferroelectric material. Its spectrum strongly varies with the internal structure with high frequency shifts of dielectric and ferroelectric modes. Even nore dramatic changes are observed in the ferroelectric-metal composite. Increasing the volume fraction of metal the surface plasmons shift to the far-infrared frequency range and start to interfere with the soft mode. It leads to the high increase of the Curie constant. The analysis is based on the quasistatic approximation and its correction due to the eddy currents is also discussed.