Modification of ZnAl2O4-based low-permittivity microwave dielectric ceramics by adding 2MO-TiO2 (M = Co, Mg, and Mn)

ZnAl2O4-based microwave dielectric ceramics with added 2MO-TiO2 (M = CO, Mg, and Mn) were synthesized using the solid-state reaction. The effects of 2MO-TiO2 additions on the microstructures, phase compositions, and microwave dielectric properties of the 0.79ZnAl(2)O(4)-0.21M(2)TiO(4) ceramics has been investigated. It can be observed from X-ray diffraction results that the single-phase solid solution in the 0.79ZnAl(2)O(4)-0.21Co(2)TiO(4) ceramics, and second-phase rutile, MgTi2O5, and ZnMn3O7 in the 0.79ZnAl(2)O(4)-0.21TiO(2), 0.79ZnAl(2)O(4)-0.21Mg(2)TiO(4), and 0.79ZnAl(2)O(4)-0.21Mn(2)TiO(4) ceramics, respectively, appear. The epsilon(r) and tau(f) values of the 0.79ZnAl(2)O(4)-0.21M(2)TiO(4) ceramics are weakly dependent on the M element (Co, Mg, and Mn). The epsilon(r) values of the 0.79ZnAl(2)O(4)-0.21M(2)TiO(4) ceramics (about 9.7) are lower than that of the 0.79ZnAl(2)O(4)-0.21TiO(2) ceramics (epsilon(r) = 11.6), whereas the tau(f) values of the former (about -65 ppm/degrees C) are higher than those of the latter (tau(f) = -0.4 ppm/degrees C. However, in contrast to the Q x f value of the 0.79ZnAl(2)O(4)-0.21TiO(2) ceramics (Q x f = 74000 GHz), the magnitude of the 0.79ZnAl(2)O(4)-0.21Co(2)TiO(4) ceramics increases to 94000 GHz and that of the 0.79ZnAl(2)O(4)-0.21Mg(2)TiO(4) ceramics improves more than twice, whereas the value of the 0.79ZnAl(2)O(4)-0.21Mn(2)TiO(4) ceramics undergoes a sharp decline and reaches a minimum of 23530 GHz at about 6.5 GHz.