Effects of structural characteristics on microwave dielectric properties of MgTi1-x(Mg1/3B2/3)xO3 (BÂ =Â Nb, Ta)

The dependence of the microwave dielectric properties of MgTi1-x(Mg1/3B2/3)xO3 (B = Nb, Ta, 0.03 ≤ x ≤ 0.20) ceramics on their structural characteristics was investigated. A single phase with the ilmenite structure was confirmed through the entire range of compositions. As the (Mg1/3B2/3)4+ content increased at the Ti4+ sites, the unit-cell volume and the average octahedral distortion increased, while the tolerance factor decreased. These results could be attributed to the decrease of both quality factor (Qf) and temperature coefficient of resonant frequency (TCF) of the specimens. MgTi1-x(Mg1/3B2/3)xO3 ceramic specimens with B = Ta5+ showed lower dielectric constant (K) and higher Qf value than those with B = Nb5+ because of their high degree of average covalency. Although the dielectric polarizability of (Mg1/3B2/3)4+ was larger than that of Ti4+, the K value of the specimens decreased linearly with (Mg1/3B2/3)4+ substitution because of the decrease of relative densities of the specimens.