Size effects on the dielectric properties of barium titanate (BaTiO3) at microwave frequencies

Dielectric measurements on BaTiO3 ceramics and BaTiO3 powder-polypropylene composites were carried out in the microwave frequency range. Lumped impedance, cavity perturbation, and post resonance techniques were employed through 5 GHz. Ceramic BaTiO3 exhibited a large relaxation with a peak in the loss centered at 771 MHz. Dielectric dispersion was also evident in the composites fabricated with similar to 1 mu m TAM HPB BaTiO3 powder, which exhibited a loss peak at 1.5 GHz. Composites fabricated with similar to 0.1 mu m Cabot BT-8 hydrothermal powder, showed a broader relaxation over the measured frequency range, with a loss peak centered at 3.2 GHz. The shift in relaxation frequency can be attributed to the reduction in particle size and subsequent modulation of the domain structure.