Effect of TiO2 and Al2O3 doping on sintering behavior and microwave dielectric properties of Ba4(Sm0.5Nd0.5)28/3Ti18+xO54+2x ceramics

The effects of TiO2 and Al2O3 doping on the phase formation, the microstructure and microwave dielectric properties of Ba6-3x (Sm1-y ,Nd (y) )(8+2x) Ti18O54 (x = 2/3 and y = 0.5; BSNT) ceramics were investigated. X-ray diffraction patterns showed that the main crystal phase of BSNT + xTiO(2) (x = 0-2) ceramics sintered at 1,280 and 1,300 A degrees C for 5 h was Ba(Sm, Nd)(2)Ti4O12, accompanied by a small number of second phases: Ba2Ti9O20 and TiO2 (x a parts per thousand yen 1.0), while the new phase BaAl2Ti5O14 appeared and the two phases Ba2Ti9O20 and TiO2 disappeared in BSNT - 2TiO(2) ceramic doped with a parts per thousand yen2 wt% Al2O3 successively as identified by scanning electron microscopy and energy dispersive spectroscopy analysis. The TiO2 and Al2O3 working as sintering aids conduced effectively to promote the densification and grain growth, and thus decreasing the sintering temperature, so when the amounts of TiO2 was increased, Q x f and tau (f) values increased continuously. The BSNT - 2TiO(2) ceramics doped with y wt% Al2O3 decreased the density and dielectric constant, increased the Q x f value remarkably and the tau (f) values was adjusted from 25.3 to -7.3 ppm/ A degrees C. When doped with 1.5 wt% Al2O3 sintered at 1,260 A degrees C for 5 h, the ceramics obtained the excellent microwave dielectric properties: epsilon (r) = 74.3, Q x f = 11,928 GHz, and tau (f) = +5.39 ppm/ A degrees C.