LAUSR

The dependence of microwave dielectric properties on the isovalent substitution of (Sn1/24+W1/26+)5+ (electronegativity difference from O2−, X = 2.16) and (Ti1/24+W1/26+)5+ (X = 1.95), with higher electronegativity differences than Nb5+ (X = 1.6) at Nb5+-sites of Mg4Nb2O9 ceramics was investigated. As expected from the electronegativity values, the quality factor of the specimens reached the highest value (274000 GHz) at X = 0.05 because Mg4Nb1.95(Sn1/2W1/2)0.05 O9 had a higher average bond valence than the other specimens. The dielectric constants (K) of the specimens were affected by the theoretical dielectric polarizability. The K value of specimens decreased with increasing x because Nb5+ has a higher dielectric polarizability (3.97 Å3) than the substitution ions such as (Sn1/2W1/2)5+ (3.015 Å3) and (Ti1/2W1/2)5+ (3.065 Å3). The effects of the structural characteristics with isovalent substitution on the microwave dielectric properties are also discussed.