Crystal structure, sintering behavior and microwave dielectric properties of CaxY3−xAl5−xTixO12 (0 ≤ x ≤ 2.0) solid solution ceramics

A novel Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution with garnet structure was synthesized by solid-state reaction technique. Ca 2+ and Ti 4+ substituted for Y 3+ and Al 3+ , respectively. Ca 2+ /Ti 4+ doping reduced the sintering temperature of Ca x Y 3−x Al 5−x Ti x O 12 ceramics to 1450 °C, and it also improved corresponding densification process. Meanwhile, the doping strongly influenced microwave dielectric properties. For the samples sintered at 1550 °C for 3 h, the dielectric constant (ε r ) increased from 7.2 to 34.7 by increasing Ca 2+ /Ti 4+ content, and at the same time the quality factor (Q × f) values increased from 12,000 to 45,200 GHz and then slightly declined to 41,000 GHz. The temperature coefficient of resonant frequency (τ f ) values of these samples increased monotonically from − 40 to + 31 ppm/°C by increasing Ca 2+ /Ti 4+ content. Therefore, Ca x Y 3−x Al 5−x Ti x O 12 solid solution ceramics with x = 1.5 sintered at 1550 °C for 3 h showed optimum microwave dielectric properties: ε r  = 32.6, Q × f = 45,200 GHz and τ f  = + 7 ppm/°C. Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution ceramics with garnet structure were new promising aluminate ceramics for microwave dielectric application.