Dielectric Properties of Porous Reaction-Bonded Silicon Nitride with Different Additives

The influence of additives on the dielectric properties of porous silicon nitride ceramics with 0.6-mm apertures and 56% porosity prepared by reaction sintering has been studied. The results show that high porosity and large apertures in porous silicon nitride ceramics lower the dielectric constant and dielectric loss compared with dense silicon nitride ceramic. α-Si₃N₄ additive is beneficial to decrease the dielectric constant and dielectric loss. Addition of Y₂O₃ and La₂O₃ powders may result in formation of Y-Si-O-N and La-Si-O-N phases, and enhance the volume fraction of β-Si₃N₄ phase. The transition of Y³⁺ and La³⁺ weakly associated ions and vacancies in the Y-Si-O-N and La-Si-O-N systems leads to higher dielectric constant and dielectric loss.