Tailoring the order-disorder transition and microwave dielectric properties of Ba[(Ni0.6Zn0.4)1/3Nb2/3]O3 ceramics by Mg-substitution

Effects of Mg-substitution on the structure, microstructure and microwave dielectric properties of Ba[(Ni0.6Zn0.4)1/3Nb2/3]O3 ceramics have been systematically investigated. Mg-substitution enhances the densification and promotes the homogenization of grain distribution. Single phase of 1:2 ordered complex perovskite structure forms in the entire composition range of Ba[(Ni0.6−x/2Zn0.4−x/2Mgx)1/3Nb2/3]O3 ceramics. Mg-substitution increases the 1:2 cations ordering degree and the ordering domain size. With increasing x, the Q × f value increases significantly, a slight decrease occurs in εr, and τf undergoes a small positive shift. Raman spectra reveal that Mg-substitution enhances the coherency of the A1g(O) vibration mode and thus improves the Q × f value. Post-densification annealing has been performed to further increase the cations ordering degree and improve the microwave dielectric properties for x = 0.3. With increasing the annealing temperature, the ordering degree increases monotonically, while the Q × f value increases first and then decreases, meanwhile εr decreases slightly and τf exhibits a negative shift. A good combination of microwave dielectric properties has been achieved for x = 0.3: εr = 32.0, Q × f = 56,500 GHz, τf = 8.4 ppm/°C.