Modified BCZN particles filled PTFE composites with high dielectric constant and low loss for microwave substrate applications

The modified 0.7Ba (Co1/3Nb2/3)O-3-0.3Ba(Zn1/3Nb2/3)O-3 (BCZN) powders filled PTFE composites were synthesized by hot-pressing. The influences of BCZN content on the microstructure, dielectric, thermal, mechanical properties and moisture absorption were investigated systematically. The modified BCZN powders filled PTFE composites exhibited better microstructure and dielectric properties compared with untreated powders. Various mathematic models were utilized to predict the dielectric constant of different composites and the effective medium theory (EMT) showed perfect consistency with the experimental results. The modified BCZN/PTFE composites possess the best comprehensive properties at the powders content of 50 vol% with high dielectric constant (epsilon(r)) of 7.7, low loss (tan delta) of 0.0014, acceptable temperature coefficient of dielectric constant (tau(epsilon)) of -125.6 ppm/degrees C and temperature coefficient of resonant frequency (tau(f)) of 29.4 ppm/degrees C at 7 GHz, low moisture absorption of 0.07% and low coefficient of thermal expansion (CTE) of 33 ppm/degrees C. All the results show modified BCZN/PTFE composites are the potential materials for microwave substrate applications.