Effects of holding time on microwave properties of Mg_4Nb_2O_9 ceramics by the solid-state process

摘要

Corundum-type magnesium niobate (Mg_4Nb_2O_9) ceramics were synthesized by the conventional solid-state method, the effect of holding time during calcination and sintering process on microwave properties was studied in detail. The xrd results showed that the major phases were identified as the ordered corundum structure Mg_4Nb_2O_9 with minor secondary phases of orthorhombic-symmetry Mg_5Nb_4O_(15). The morphology was obviously affected by holding times at sintering process and the relationships between the morphology and microwave properties were discussed. The results indicated that holding time at calcination process had negligible effect on the microstructure and microwave properties, while holding time at sintering process could obviously affect the microstructure and microwave properties of Mg_4Nb_2O_9. When calcination at 1100°C for 2h and sintered at 1350°C for 6h, the optimal microwave properties were ε_r~13, Q?f~130,000GHz and τ_f~50 ppm/°C.