Tungsten bronze type structure, atmosphere sensitivity and microwave dielectric properties of Ba4(CexSm1−x)9.3Ti18O54 ceramics

The phase structure, ions valence state and microwave dielectric properties of Ba 4 (Ce x Sm 1− x ) 9.3 Ti 18 O 54 (0 ≤ x ≤ 0.9, BCST) ceramics sintered in air and nitrogen have been investigated. BCST ( x ≤ 0.1) ceramics sintered in air only exhibited peaks associated with tungsten bronze phase structure. A secondary CeO 2 phase appeared for x = 0.5, while CeO 2 and Ba 2 Ti 9 O 20 phases coexisted for the ceramics with x = 0.9. In contrast, ceramics fired in nitrogen exhibited tungsten bronze phase structure for all compositions from x = 0 to 0.9 within the solid solution. The chemical structure analysis exhibited that, all the sample possessed mixed ion valance states of Ce 4+ /Ce 3+ and Ti 4+ /Ti 3+ cations upon oxygen vacancy formations. It is found that incorporation of cerium could significant improve the Q × f values of BCST ceramics sintered in nitrogen with good microwave dielectric properties ( Q × f ∼7536 GHz, ε r ∼78, and τ f ∼24.61 ppm/°C) at x = 0.5.