Dielectric properties of PTFE loaded with micro- and nano-Sm2Si2O7 ceramics

The present study compares the dielectric and thermal properties of PTFE loaded with Sm2Si2O7 filler of varying filler size. The composites were prepared by powder processing technique followed by hot pressing. The variation of the dielectric properties with filler content (0-0.25 v(f)) was studied at 1 MHz and 9 GHz. The microstructural study using scanning electron microscopy showed that the nano size fillers were uniformly dispersed in the matrix as compared to that of the micron size. The PTFE loaded with 0.25 v(f) micro Sm2Si2O7 composites showed a relative permittivity and dielectric loss of 3.51, 0.00155 whereas for nano Sm2Si2O7 composites with same volume fraction the values were 4.35, 0.04861 respectively at 1 MHz. The experimental values of relative permittivity were compared with various theoretical models, and the modified Lichtenecker equation and Effective Medium Theory were found to be in good agreement for both the composites even for higher filler content. Furthermore, the comparison of thermal expansion coefficient of the PTFE/Sm2Si2O7 composites implies a much lower CTE value for nano fillers.