Low dielectric loss LNT/PEEK composites with high mechanical strength and dielectric thermal stability

Abstract (3‐Aminopropyl)triethoxysilane treated La _{(2− x )/3} Na _0.06 TiO ₃ ( x = 0.06) (LNT) microparticles filled polyetheretherketone (PEEK) composites were prepared using hot pressing process. The effects of variation of LNT ceramic filling fraction on dielectric properties, water absorption, thermal stability and mechanical strength were investigated. All composites demonstrate low water absorption (less than 0.4%) when the ceramic filling fraction is lower than 0.6V _f . The obtained composites exhibited dielectric permittivities varying from ~4 to ~22 as the ceramic fillers increased from 0.1 to 0.8 V _f and low losses (~10 ⁻⁴ @1 MHz, 3~5 × 10 ⁻³ at the frequencies of microwave (10 GHz) and millimeter wave (29‐50 GHz), respectively). The mechanical strength, dimensional and dielectric thermal stability of the composite are remarkably improved by the addition of LNT ceramic fillers. A composite with near zero temperature coefficients of dielectric permittivity or resonant frequency and flexural strength of ~140 MPa could be obtained. The out‐of‐plane coefficient of thermal expansion (CTE) could be reduced to ~20 ppm/°C as the ceramic filler loading reached 0.7 V _f .