Compositional effects of Nb site on microwave dielectric properties of Mg4(Nb,Ta,Sb)2O9 ceramics

The relationships between the structural characteristics and the microwave dielectric properties of the specimens with stoichiometric and non-stoichiometric substitutions were investigated. A single phase with a corundum structure was observed for all compositions of specimens sintered at 1400 degrees C for 5 h. The microwave dielectric properties of the sintered specimens strongly depended on the type and content of pentavalent cations (e.g., Na5+, Ta5+, Sb5+) in Mg-4(NbxTaySbz)O-9 ceramics. The Qf value of specimens with stoichiometric substitutions at the Nb site of Mg4Nb2O9 depended on the B-site (i.e., Nb site) bond valence, whereas that of specimens with non-stoichiometric substitutions depended on the packing fraction of the unit cell. The dielectric constants (K) of the specimens did not change remarkably with the composition, and the temperature coefficient of resonant frequency (TCF) depended on the average octahedral distortion.