Phase compositions and crystal structure of Sn-deficient Ca2Sn2Al2O9 microwave dielectric ceramics with high Q×f values

The phase compositions and microwave dielectric properties of Sn-deficient Ca 2 Sn 2 Al 2 O 9 ceramics in this study were explored. The CaSnO 3 and SnO 2 second phases existed at Ca 2 Sn 2- x Al 2 O 9-2 x ( x  = 0) ceramic. Single-phase Ca 2 Sn 2 Al 2 O 9 ceramics were obtained at 0.08 ≤  x  ≤ 0.1, and the orthorhombic structure with the Pbcn space group of Ca 2 Sn 2 Al 2 O 9 was verified. For multi-phase Ca 2 Sn 2- x Al 2 O 9-2 x (0 ≤  x  ≤ 0.06) ceramics, their microwave dielectric properties were mainly affected by second phase contents, and their Q  ×  f values increased gradually with the rise in x . High Q  ×  f (105,700 GHz at 12.99 GHz) was obtained by the Ca 2 Sn 2- x Al 2 O 9-2 x ( x  = 0.08) ceramic with high intrinsic Q  ×  f (175,000 GHz). The large deviation between measured Q  ×  f values and fitted intrinsic Q  ×  f values could be ascribed to the Sn 4+ vacancies of the Sn-deficient Ca 2 Sn 2 Al 2 O 9 ceramics. The Ca 2 Sn 2- x Al 2 O 9-2 x (0 ≤  x  ≤ 0.1) ceramics presented large negative τ f values, and this τ f was mainly affected by τ ε . Meanwhile, the Ca 2 Sn 2- x Al 2 O 9-2 x ( x  = 0.08) ceramic achieved optimal microwave dielectric properties ( ε r  = 8.3, Q  ×  f  = 105,700 GHz at 12.99 GHz and τ f  = −63.7 ppm/°C), indicating the good feature of this material for millimetre-wave applications.