Effects of MgO additive on microwave dielectric properties of NdNbO4 ceramics.

NdNbO₄−x MgO (x = 0.5, 1.0, 2.0, 3.0, 4.0) ceramics with high Q × ƒ values were prepared via the conventional solid-state reaction. The effects of MgO additive on the microstructures and microwave dielectric properties of NdNbO₄ ceramics were investigated through various approaches. Microscopic analysis showed that the NdNbO₄ phase and MgO phase were coexisted, and the crystal structure of the two phases did not changed with the additional amount of MgO. The dielectric constant could be explained by bulk density as a function of sintering temperature and satisfied with the Lichtenecker logarithmic superposition rule. The Q × ƒ value increased quickly when the phase composition changed from single phase to multiphase and was afterwards linked to the grain growth. The change in the temperature coefficient of resonant frequency was not large and was consistent with that in the dielectric constant. When x = 3.0, MgO additive effectively stepped up the Q × ƒ value of NdNbO₄ to 1,35,000 GHz, which was fourfold of pure phase. [ABSTRACT FROM AUTHOR]