Effect of secondary phases' structure on the dielectric properties of β-SiAlON

This study investigates the effect of secondary phases microstructure on mechanical and dielectric properties in beta silicon aluminum oxy-nitride (beta-SiAlON) produced by pressureless sintering at temperatures of 1650 degrees C-1750 degrees C from a mixture of silicon nitride (Si3N4), alumina (Al2O3), aluminum nitride (AlN) and yttrium oxide (Y2O3). beta-SiAlON obtained at and above 1700 degrees C sintering temperature, which showed a fully dense structure with a good combination of hardness and strength of 21-23 GPa and 870-890 MPa, respectively. Surprisingly, the dielectric constant of beta-SiAlON was found to increase significantly from 6.4 to 8.2 with an increase in the sintering temperature from 1700 to 1750 degrees C. Transmission electron microscopy revealed the presence of secondary crystalline phase yttrium rich silicon aluminum oxynitride in the specimen sintered at 1750 degrees C, whereas yttrium rich amorphous interface structure was found in the specimen sintered at 1700 degrees C, suggesting the importance of controlling grain boundary structures in beta-SiAlON.