Tungsten bronze type structure, atmosphere sensitivity and microwave dielectric properties of Ba_4(Ce_xSm_(1-x))_(9.3)Ti_(18)O_(54) ceramics

摘要

The phase structure, ions valence state and microwave dielectric properties of Ba_4(Ce_xSm_(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_2Ti_9O_(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 Qxf 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/℃) at x = 0.5.