Effect of filler content on the dielectric properties of PTFE/ZnAl2O4-TiO2 composites

ZnAl2O4-TiO2 (ZAT)/polytetrafluoroethylene (PTFE) composites were prepared by powder processing method. The structure and microstructure of the composites were analyzed using X-ray diffraction and scanning electron microscopic techniques. The effect of different volume fraction of ZAT (0-0.6) on the dielectric properties of the composites was investigated at I MHz and at the microwave frequency of 7 GRz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ZAT content. The samples with 60 vol.% of ZAT filler showed a relative permittivity of 3.9 and dielectric loss of 0.009, respectively, at 7 GHz. The variation of relative permittivity and dielectric loss showed only a very small variation with temperature in the range 25 degrees-70 degrees C for various ZAT/PTFE composites. The relative permittivity obtained experimentally were compared with that of the theoretical values predicted using modified Lichtenecker, Jayasundere-Smith, and Series mixing formulae. They were found to agree well with the predicted values for low filler content.