Low dielectric loss BST/PTFE composites for microwave applications

Ba0.3Sr0.475Ce0.03La0.12Ti0.997Mn0.003O3/Polytetrafluoroethylene (PTFE) composites were prepared using powder processing technique. The effects of the ceramic filler volume fraction and the coupling agent on the phase composition, microstructure, dielectric and thermal properties of the composites were investigated in this paper. The ceramic filler dispersion in the PTFE matrix, thus the dielectric loss, permittivity, and dimensional thermal stability of the composite was considerably improved by the modification of BST filler surface using phenyl trimethoxy silane (PTMS) coupling agent. Variation of the dielectric permittivity of the composite with composition was well fitted by the effective medium theory (EMT) model in the experimental compositional range. The obtained silane-treated composite with 0.5 V-f BST exhibits extremely low dielectric loss: epsilon(r) = 16, tan delta = 5.4 x 10(-4) @1 MHz and 5.16 +/- 0.6 x 10(-3) @ 10 GHz. The CTE of the composites was reduced to 43 ppm/degrees C.