Ni4Nb2O9 ceramics prepared by the reaction-sintering process

Fabrication of Ni4Nb2O9 ceramics via a reaction-sintering process was investigated. A mixture of raw materials was sintered into ceramics by bypassing calcination and subsequent pulverization stages. Ni4Nb2O9 phase appeared at 1300 °C and increased with increasing soak time. Ni4Nb2O9 content was found >96% in 1350 °C/2 h sintering pellets. A density of 5.71 g/cm3 was obtained for pellets sintered at 1350 °C for 2 h. This reaches 96.5% of the theoretical density. As the sintering temperature increased to 1350 °C, an abnormal grain growth occurred and grains >100 μm could be found. ɛr of 15.4–16.9 are found in pellets sintered at 1200–1300 °C. Q × f increased from 9380 GHz in pellets sintered at 1200 °C to 14,650 GHz in pellets sintered at 1250 °C.