Modification And Mechanism Of Ba(Mg_1/3Nb_2/3)O₃ Based Microwave Dielectric Ceramics

Microwave medium ceramic refers to the ceramic applied as a medium material and completes certain functions in microwave frequency band circuit,and is a new functional ceramic material developed in the past 30 years.The advent of the 5G era has put forward higher requirements for the dielectric properties of microwave media ceramics:adjustable dielectric constants（ε_r）,low dielectric loss（high Q×f）and low resonance frequency temperature coefficients（τ_f）.Ba(B’_1/3B’’_2/3)O₃-type(B’=Zn²⁺,Mg²⁺,Ni²⁺,Co²⁺;B’’=Ta⁵⁺,Nb⁵⁺),the composite calcium-titanium-type ceramic is one of the high-frequency microwave medium ceramics that has been studied more.Among them,tantalum-based composite calcium and titanium ore materials such as Ba(Mg_1/3Ta_2/3)O₃ and Ba(Zn_1/3Ta_2/3)O₃ are of great concern because of their excellent dielectric properties.However,the Ta₂O₅is expensive and difficult to meet the growing production demand for microwave ceramic devices.Ba(Mg_1/3Nb_2/3)O₃ has good microwave performance:ε_r=32,Q=5600（10.5 GHz）,τ_f=+33 ppm/℃,and is expected to be a candidate for tantalum-based microwave media ceramics.However,there is still a big gap between the microwave dielectric performance of BMN ceramics and the performance of Ta-based microwave medium ceramics,and the resonant frequency temperature coefficient is a large positive value（+33 ppm/℃）,which is a major obstacle to the commercial application of Ba(Mg_1/3Nb_2/3)O₃ceramics.Based on the combination of theoretical analysis and literature research,this paper uses ionic substitution and two-phase composite method to make a modified study of Ba(Mg_1/3Nb_2/3)O₃ ceramics.On the basis of Ba(Mg_1/3Nb_2/3)O₃ ceramic mixed with quantitative Basn O₃,the Mg₄Nb₂O₉phase was further introduced,and the influence of Mg₄Nb₂O₉ on Ba(Mg_1/3Nb_2/3)O₃-based ceramic crystal structure,sintering performance and microwave dielectric performance was studied.The results show that the addition of Mg₄Nb₂O₉ phase reduces the sintering density temperature of Ba(Mg_1/3Nb_2/3)O₃-based ceramics and improves the microwave dielectric performance of ceramics.Ceramics get the best dielectric performance when the Mg₄Nb₂O₉complex-phase volume x is 0.045 and the sintering temperature is 1450℃:ε_r=28.78,Q×f=97 000 GHz,τ_f=5.2 ppm/℃.Under the chemical metering ratio of 0.974Ba(Mg_1/3Nb_2/3)O₃-0.026Mg₄Nb₂O₉,Ta⁵⁺was doped for B-site substitution.The effects of B-bit replacement on Ba(Mg_1/3Nb_2/3)O₃-based ceramic crystal structure,sintering properties and microwave dielectric properties are studied.Experiments show that a small amount of Ta⁵⁺plus can improve the Q×f value of ceramics,when the Ta⁵⁺plus ion doping x=0.1,sintering temperature of 1360℃,the Q×f value of ceramics reached a maximum of 104 000 GHz;The replacement of Ta⁵⁺plus effectively reduces theτ_f value of the ceramic,and when the amount of Ta⁵⁺plus ions is x=0.4,theτ_f value of the ceramic is reduced to 11.04 ppm/℃.Under the 0.9Ba(Mg_1/3Nb_2/3)O₃-0.1Ba Sn O₃ chemical metering ratio,the effect of A-site substitution on the microstructure,sintering characteristics and microwave dielectric properties of Ba(Mg_1/3Nb_2/3)O₃ based ceramics was investigated by adding trace Ca²⁺to replace Ba²⁺.The sintering temperature of 1490℃is the best performance when the Ca²⁺plus doping concentration is 1 mol%,with the highest performance:ε_r=30.43,Q×f=76 000 GHz,τ_f=24.65 ppm/℃,the resonant frequency temperature coefficient of the ceramicτ_f with a minimum value of 19.1 ppm/℃when Ca²⁺plus doping is 0.5 mol%.Ba(Mg_1/2W_1/2)O₃has a calcium-titanium structure similar to Ba(Mg_1/3Nb_2/3)O₃ and has a large negative temperature coefficient（τ_f=-25 ppm/℃）.According to the method of cross-series mixing of complex-phase ceramics,the introduction of a moderate amount of Ba(Mg_1/2W_1/2)O₃in the Ba(Mg_1/3Nb_2/3)O₃ system can adjust the resonant frequency temperature coefficient close to zero.The two-phase composite method is used to prepare（1-x）Ba(Mg_1/3Nb_2/3)O₃-x Ba(Mg_1/2W_1/2)O₃composite ceramic by incorporating Ba(Mg_1/2W_1/2)O₃.The results show that when Ba(Mg_1/2W_1/2)O₃complex phase mass x=0.15,sintering temperature is 1520℃,ceramics have a maximum Q×f value of 85 000 GHz,ε_r=30.38,τ_f=13.59 ppm/℃.