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Aluminum nitride (AlN) ceramics were sintered with spark plasma sintering (SPS) technique using Y 2 O 3 (Sm 2 O 3 )–CaF 2 as the sintering additives. The purification effect of sintering additives, dielectric properties, microstructure and polarization mechanism of AlN ceramics were investigated. The densification process curves indicate that both sintering additive and special SPS sintering mechanism are conductive to reducing the sintering beginning temperature. The results of lattice parameters of AlN ceramics suggest that suitable sintering additives have prominent purification effect on the crystal lattice of AlN ceramics. Dielectric constant increases with Y 2 O 3 (Sm 2 O 3 ) content increasing, and the AlN ceramic containing 2 wt.% Sm 2 O 3 -1 wt.% CaF 2 exhibits the lowest dielectric loss. Oxygen impurities, dislocation and amorphous layer in the crystal structure of AlN ceramics increase dielectric loss of AlN ceramics. The space charge polarization caused by secondary phases and other defects might be the main polarization mechanism of AlN ceramics. [ABSTRACT FROM AUTHOR]