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Influence of Chemical Composition and Y2O3 on Sinterability, Dielectric Constant, and CTE of -SiAlON

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Different types of dense -Si6−zAlzOzN8−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 -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 -Si4Al2O2N6 exhibited a BD of ∼3.06 g/mL, AP of ∼0.01%, WA capacity of ∼0.01%, ∼94.43%-SiAlON phase, a hardness of ∼1317 kg/mm2, a fracture toughness of ∼3.30 MPa·m1/2, 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.
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Document Type: Research Article

Affiliations: Centre for Silicon Carbide, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500 005, Andhra Pradesh, India

Publication date: January 1, 2008

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