Abstract

This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg₄Nb₂O₉-(0.3-x)ZnAl₂O₄-xTiO₂ ternary system. Crystalline phases and microstructure of Mg₄Nb₂O₉-ZnAl₂O₄-TiO₂ dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti⁴⁺ substituted Nb⁵⁺ in the Mg₄Nb₂O₉ structure, which promoted the decomposition of Mg₄Nb₂O₉ to form the second phase, Mg₅Nb₄O₁₅, during sintering. The synergistic effect of ZnAl₂O₄-TiO₂ co-doping promoted the Mg₄Nb₂O₉ ceramic densification. The sample (0.7Mg₄Nb₂O₉-(0.3-x)ZnAl₂O₄-xTiO₂) with x = 0.15−0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl₂O₄, Mg₄Nb₂O₉ and Mg₅Nb₄O₁₅, due to the NbO₆ octahedra distortion resulting from the substitution of Al³⁺/Ti⁴⁺ for Nb⁵⁺ in Mg₄Nb₂O₉ and Mg₅Nb₄O₁₅. The long-range order of the NbO₆ octahedra was enhanced by co-doping ZnAl₂O₄ and TiO₂, thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τf of −60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg₄Nb₂O₉-0.15ZnAl₂O₄-0.15TiO₂. These results show that 0.7Mg₄Nb₂O₉-0.15 ZnAl₂O₄-0.15TiO₂ ceramic is a good candidate for microwave electronic device applications.