Optimized phase compositions and microwave dielectric properties of low loss Ca2Sn2Al2O9-based ceramics by M4+ substitution
The traditional solid-state reaction method was used to prepare Ca 2 Sn 2− x M x Al 2 O 9 (M = Ti, Zr, and Hf) ceramics. Then, the impact of an M 4+ substitution of Sn 4+ on the phase transition, crystal structural parameter, and microwave dielectric properties of Ca 2 Sn 2− x M x Al 2 O 9 (0 ≤ x ≤ 0.4) ceramics were investigated. Ti 4+ could not replace the Sn 4+ of Ca 2 Sn 2 Al 2 O 9 due to its small ionic radius, and the Al-based second phases of Ca 2 Sn 2− x Ti x Al 2 O 9 ceramics were confirmed by the X-ray diffractometer and EDS map scanning results. With the Zr 4+ and Hf 4+ substitutions of Sn 4+ , the SnO 2 and CaSnO 3 second phases of Ca 2 Sn 2 Al 2 O 9 ceramic were inhibited, and the Ca 2 Sn 2− x M x Al 2 O 9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) single-phase ceramics with orthorhombic structure ( Pbcn space group) were obtained. New MO 2 (M = Zr and Hf) and CaAl 2 O 4 second phases appeared in the Ca 2 Sn 2− x M x Al 2 O 9 (M = Zr and Hf) (0.3 ≤ x ≤ 0.4) ceramics, and their contents increased gradually with the increase in x . The Ca 2 Sn 2− x M x Al 2 O 9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) ceramics exhibited high Q × f because of their pure phase compositions, and the Q × f of Ca 2 Sn 2 Al 2 O 9 ceramic was improved to 77 800 GHz (12.6 GHz) in the Ca 2 Sn 1.9 Zr 0.1 Al 2 O 9 ceramic. The Q × f values of Ca 2 Sn 2− x M x Al 2 O 9 single-phase ceramics were mainly controlled by r c (Sn/M–O) and r c (Al–O). The τ f values of single-phase Ca 2 Sn 2− x M x Al 2 O 9 ceramics were related to octahedral distortions. The Zr 4+ and Hf 4+ substitution of Sn 4+ optimized the phase compositions and microwave dielectric properties of the Ca 2 Sn 2− x M x Al 2 O 9 ceramics, and the Ca 2 Sn 1.9 Zr 0.1 Al 2 O 9 ceramic sintered at optimal temperature exhibited excellent microwave dielectric properties ( ε r = 8.67, Q × f = 77 800 GHz at 12.6 GHz and τ f = −69.8 ppm/°C).
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