Anti-reduction of Ti4+ in Ba4.2Sm9.2Ti18O54 ceramics by doping with MgO, Al2O3 and MnO2

Abstract The anti-reduction of Ti 4+ ions in Ba 4.2 Sm 9.2 Ti 18 O 54 (BST) ceramics at high sintering temperature over 1300 °C was investigated. MgO, Al 2 O 3 and MnO 2 were added separately to suppress the reduction of Ti 4+ ions so as to improve the microwave dielectric properties of BST ceramics. The microstructure of BST ceramics was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to study the electroconductivity of BST ceramics and valency changes of Ti ions. The results showed that MgO or Al 2 O 3 , when acting as an acceptor, could effectively suppress the reduction of Ti 4+ ions and significantly improve the Q × f values of BST ceramics at the cost of dielectric constant. Meanwhile, MnO 2 as an oxidant had also improved the Q × f values but with no decrease in dielectric constant. Excellent microwave dielectric properties were achieved in Ba 4.2 Sm 9.2 Ti 18 O 54 ceramics doped with 0.2 wt.% Al 2 O 3 sintered at 1340 °C for 3 h: ɛ r = 76.9, Q × f = 10,120 GHz and τ f = −22.7 ppm/°C.