Low dielectric loss ceramics in the Mg4Nb2O9-ZnAl2O4-TiO2 ternary system

This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg(4)Nb(2)O(9)-(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 (0.7Mg(4)Nb(2)O(9)-(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 tau(f) of -60.8 ppm/degrees C were obtained from 1300 degrees C sintered 0.7Mg(4)Nb(2)O(9)-0.15ZnAl(2)O(4)-0.15TiO(2). These results show that 0.7Mg(4)Nb(2)O(9)-0.15 ZnAl2O4-0.15TiO(2) ceramic is a good candidate for microwave electronic device applications.