Preparation And Properties Of Silicon Nitride Matrix Composite Ceramics Added With High Dielectric Material

CaTiO₃-Si₃N₄ composite ceramics and BaTiO₃-Si₃N₄ composite ceramics which have good comprehensive performance were prepared by adding CaTiO3 and BaTiO3 to Si3N4 by gas pressure sintering respectively.CaTiO₃-Si₃N₄ composite ceramics added with 15 wt.% CaTiO3 and BaTiO₃-Si₃N₄ composite ceramics added with 15 wt.% BaTiO3 were prepared by using the gas pressure sintering process at the sintering temperature of 1650 ?,1700 ?,1750 ?,under the sintering pressure of 4 MPa and the holding time of 2 hours.The results show that the flexural strength,dielectric constant and dielectric loss of the ceramic material increase with the increase of sintering temperature.The increase of sintering temperature promotes to the densification of Si3N4 based composite ceramics and improves the dielectric properties of ceramics.Thus,the final sintering temperature was determined to be 1750 ?.CaTiO₃-Si₃N₄ composite ceramics were prepared by gas pressure sintering at the sintering temperature of 1750 ?,under the sintering pressure of 4MPa and the holding time of 2 hours.The effects of the addition of CaTiO3 on the mechanical properties,dielectric properties and microstructure of the composite ceramics were studied.The experimental results show that when the introducing content of CaTiO3 reaches 15 wt.%,the flexural strength,elastic modulus,fracture toughness,density,porosity and shrinkage rate of the composite ceramics reaches the maximum value: 246 GPa,6.9 MPa·m1/2,3.29 g/cm3,2.7%,20.43%,respectively.The dielectric constant increases from7.6 to 9.6 with the increase of the content of CaTiO3 and the dielectric constant of the sample is almost constant at the test frequency of 10 12 GHz.The overall dielectric loss decreases with the increase of CaTiO3 and the dielectric loss change between 0.0034 and 0.016.The silicon nitride-based composite ceramics doped with 15 wt.% CaTiO3 satisfies the requirements of Si3N4-based composite ceramics with ? greater than 8,tan? less than 0.01 and flexural strength higher than 580 MPa.BaTiO₃-Si₃N₄ composite ceramics were prepared by gas pressure process at the sintering temperature 1750 ?,under the sintering pressure 4MPa and the holding time for 2 hours.The experimental results show that when the introducing content of BaTi O3 reaches 15 wt.%,the flexural strength,elastic modulus,fracture toughness,density,porosity and shrinkage rate of the composite ceramics reaches the maximum value: 814 MPa,243 GPa,8.21 MPa·m1/2,3.29 g/cm3,1.9%,19.08%,respectively.The dielectric constant increases from7.0 to 8.9 with the increase of the content of BaTiO3 and the dielectric constant of the sample is almost constant at the test frequency of 10 12 GHz.The overall dielectric loss decreases with the increase of BaTiO3 and the dielectric loss change between 0.002 and 0.024.The silicon nitride-based composite ceramics doped with 15 wt.% CaTiO3 satisfies the requirements of Si3N4-based composite ceramics with ? greater than 8,tan? less than 0.01 and flexural strength higher than 580 MPa.