Influence of chemical composition and Y₂O₃ on sinterability, dielectric constant, and CTE of β-SiAlON

Abstract

Different types of dense β-Si_6-zAl_zO_zN_8-z (z=1, 1.5, 2, 2.5, 3, 3.5, and 4) ceramics have been prepared following a conventional reaction sintering process at 1675°-1700°C using α-Si₃N₄, α-Al₂O₃, AlN, and 3-7-wt% Y₂O₃ as raw materials. Sintered materials were thoroughly characterized for bulk density (BD), apparent porosity (AP), water absorption (WA) capacity, phase formation, microstructure, coefficient of thermal expansion (CTE), hardness, fracture toughness, three-point bent strength, and dielectric constant at 16-18 GHz frequency. Characterization results suggest that an increase in z value, Y₂O₃ concentration, and sintering temperature leads to an increase in β-SiAlON phase formation, BD, grain size, fracture toughness, and dielectric constant, and as a consequence, AP, WA capacity, hardness, and three-point bend strength of the materials decrease. These materials also exhibited stable and low dielectric constants (5.67-7.67) between 16 and 18 GHz frequency. The β-Si₄Al₂O₂N₆ exhibited a BD of ~3.06 g/mL, AP of ~0.01%, WA capacity of ~0.01%, ~94.43%β-SiAlON phase, a hardness of ~1317 kg/mm², a fracture toughness of ~3.30 MPa·m^1/2, a three-point bend strength of ~226 MPa, a CTE of 3.628 × 10⁻⁶°C⁻¹ between 30° and 700°C, and a dielectric constant of ~7.206 at 17 GHz after sintering at 1675°C for 4 h with 7-wt% Y₂O₃.