Dielectric response of BaTiO3-filled epoxy resin processed by dipping

LEANDRO RAMAJO; MARIA MARTA REBOREDO; MIRIAM SUSANA CASTRO

Foz do Iguazú, Brasil

Simposio; Encontro da SBPMat; 2004

The dielectric behaviour of composite materials (epoxy resin – barium titanate) was analysed as a function of ceramic content. Epoxy and Nb2O5-doped BaTiO3 were chosen because of their good dielectric properties. The ceramic was milled in isopropilic medium using a planetary mill with ZrO2 balls for 90 min to obtain better dispersion during the mixing. Particles size distributions were determined and lattice parameters were characterised by X-Ray Diffraction, while the resin was characterised by scanning differential calorimetry (DSC). Epoxy was diluted using tetrahydrofuran (THF, 60% wt) as solvent in order to reduce matrix viscosity and to facilitate the mixing step. Once the ceramic particles were mixed with the resin, dipping technique was used to obtain the composite films onto glass plates on which gold electrodes were deposited by sputtering. After that, the system was cured at 100ºC during 2 hours. Dielectric measurements were performed from 25 Hz to 1 MHz and 25ºC to 120ºC. It was found that the final materials had high permittivities and a strong dependence with the filler concentration. The peaks (a) were shifted to higher frequencies because relaxation processes were influenced by interfacial polarisation effect, known as Maxwell-Wagner-Sillar. Electrical relaxation a generated by resin dominions was detected in the composites and it was influenced by temperature (principally near the resin glass transition temperature, Tg).