Microwave Dielectric Properties of (Mg_1-xNi_x)(Ti_0.95(Mg _1/3Ta_2/3)_0.05)O₃ Ceramics

The effects of Ni2+ substitution for Mg2+-sites on the microwave dielectric properties of (Mg1-xNix)(Ti-0.95(Mg-1/3 Ta-2/3)(0.05))O-3 (0.01 <= x <= 0.05) (MNTMT) ceramics were investigated. MNTMT ceramics were prepared by conventional solid-state reaction. When the MgO / TiO2 ratio was changed from 1.00 to 1.02, MgTi2O5 was detected as a secondary phase along with the MgTiO3 main phase in the MNTMT specimens sintered at 1,400 degrees C for 4h. For the MNTMT specimens with MgO / TiO2 = 1.07 sintered at 1,400 degrees C for 4h, a single phase of MgTiO3 with an ilmenite structure was obtained from the entire range of compositions. The relative density of all the specimens sintered at 1,400 degrees C for 4h was higher than 95 %. The quality factor (Qf) of the sintered specimens depended strongly on the degree of covalency of the specimens, and the sintered specimens with x = 0.01 showed the maximum Qf value of 489,400 GHz. The dielectric constant (K) decreased with increasing Ni2+ content because Ni2+ had a lower dielectric polarizability (1.23 angstrom(3)) than Mg2+ (1.32 angstrom(3)). As Ni2+ content increased, the temperature coefficient of resonant frequency (TCF) improved, from -55.56 to -21.85 ppm/degrees C, due to the increase in tolerance factor (t) and the lower dielectric constant (K).