Structural Characteristics And Microwave Dielectric Properties Of Ba(Mg_1/3Nb_2/3)O₃Ceramics

Microwave dielectric ceramics with high dielectric constant (εr) and high quality factor (Q) and small temperature coefficient of the resonance frequency of (τf), are a kind of functional ceramics. Microwave dielectric ceramics have been developed for near30years, are key material used in microwave components such as resonators, filters, the dielectric antenna and dielectric waveguide loops. As the rapid development of mobile communications and satellite communications, the dielectric loss of materials are demanded smaller in the high frequency. Civil microwave components are used at higher microwave frequency. Microwave dielectric ceramics requires not only excellent microwave properties but also low price. More and more attention to the Ba(B'1/3B"2/3)03(B'=Mg,Zn,Ni,Co; B"=Ta,Nb) composite ceramics, because of the low dielectric loss in the high frequency. But the cost of industrial greatly increased as the oxidation tantalum is very expensive. Instead, the oxidation niobium relatively inexpensive, and niobium acid salt ceramics has higher dielectric constant, lower the sintering temperature.The effect of process parameters and chemical ratios on the structure and the microwave dielectric properties of Ba(Mg1/3Nb2/3)03ceramics, which were prepared by the mixed oxide route. In this paper, the effect of microstructure on the microwave dielectric properties of Ba(Mg1/3Nb2/3)O3ceramics.the effect of B-site nonstoichiometry on the microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3ceramics was researched.The results of the study show that:An improvement of the degree of1:2ordering and sinterability was found in Mg-defieient Ba(Mg1/3Nb2/3)O3ceramics, because there existed Mg vaeancies promoted the movement of grain boundary, which can improved the sinterability and the degree of1:2ordering. The Mg-defieient makes the crystal cell parameters change, and make the crystal structure more close to the ideal of the six party perovskite structure.The nature of the B-site cation ordering and the associated defect process necessary to stabilize the ordered domains were investigated using the WO3-doped Ba(Mg1/3Nb2/3)O3. It was shown that only the1:2long-range ordering of the B-site cation existed in both undoped and WO3-doped Ba(Mg1/3Nb2/3)O3perovskites. The substitution of W6+for Nb5+in the WO3-doped Ba(Mg1/3Nb2/3)O3enhanced the degree of the1:2long-range ordering and produces the positively charged WNb· sites with a concomitant generation of niobium vacancies (VNb(?)) and mobile oxygen vacancies (Vo(?)) for the ionic charge compensation.