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

Abstract This study investigates the effect of secondary phases microstructure on mechanical and dielectric properties in beta silicon aluminum oxy-nitride (β-SiAlON) produced by pressureless sintering at temperatures of 1650 °C–1750 °C from a mixture of silicon nitride (Si 3 N 4 ), alumina (Al 2 O 3 ), aluminum nitride (AlN) and yttrium oxide (Y 2 O 3 ). β-SiAlON obtained at and above 1700 °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 β-SiAlON was found to increase significantly from 6.4 to 8.2 with an increase in the sintering temperature from 1700 to 1750 °C. Transmission electron microscopy revealed the presence of secondary crystalline phase yttrium rich silicon aluminum oxynitride in the specimen sintered at 1750 °C , whereas yttrium rich amorphous interface structure was found in the specimen sintered at 1700 °C, suggesting the importance of controlling grain boundary structures in β-SiAlON.