Effects of Ball Milling Time on the Microwave Properties of Mg4Nb2O9 Ceramics by the Solid-State Process

Corundum-type magnesium niobate (Mg4Nb2O9) ceramics were synthesized by the conventional solid-state method, the effect of ball milling time on microwave properties was studied in detail. Xrd results showed that the major phase was identified as the ordered corundum structure Mg4Nb2O9 with minor secondary phase of orthorhombic-symmetry Mg5Nb4O15. The morphology was obviously affected by ball milling times at sintering process, and then the relationships between the morphology and microwave properties were discussed. The results indicated that ball milling times at sintering process could obviously affect the microstructure and microwave properties of Mg4Nb2O9 ceramics. When ball milling time was 10h, the Mg4Nb2O9 ceramics were prepared with the conditions of calcination at 1100°C for 2h and sintered at 1350°C for 6h, and the optimal microwave properties were er~13, Q·ƒ~120,000GHz and ƒ~-60ppm/°C.