Preparation And Microwave Dielectric Properties Of Magnesium Tantalate Based Ceramics With Ultra-high Q Values

Microwave dielectric ceramics are a kind of functional ceramics,which have suitable permittivity??_r?,high Qf values,and near zero resonance frequency temperature coefficient??_f?.It has been widely used to make various resonators,dielectric waveguides,microwave antennas,microwave filters?diplexers?,dielectric substrates and dielectric capacitors.In recent years,with the rapid development of 5G communications and satellite communications,traditional microwave dielectric ceramics such as Ba Ti₄O₉,?Zr,Sn?Ti O₄,Ba O-Ln₂O₃-Ti O₂ haven't been able to meet the urgent application requirements of new generation communication technology.So it is necessary to develop new microwave dielectric ceramics with low?_r?<20?,ultra-high Qf value??100000 GHz?and?_fnear zero.However,although low?_r microwave dielectric ceramics have super-high Qf values,its negative?_f can not meet the latest development requirements.It is necessary to be compounded with ceramics with high Qf value and positive?_f,and adjust the?_f to near zero.Therefore,it is urgent to research and develop microwave dielectric ceramics with high Qf values and positive?_f to meet the great demand of current communication technology.In this paper,Mg Ta₂O₆ ceramics were taken as the research object.The preparation process,composition design,structure and dielectric properties control of those single-phase and multi-phase systems were mainly studied.The following important research results were obtained:?1?The preparation process and microwave dielectric properties of single-phase Mg Ta₂O₆ ceramics were studied.It was clear that the residual Ta₂O₅ phase in Mg Ta₂O₆ceramics was the main reason for its low dielectric properties;the residual Ta₂O₅ phase can be effectively eliminated by adding B₂O₃ and Mg O,and then single-phase Mg Ta₂O₆ceramics can be prepared which microwave dielectric properties were significantly improved,especially the Qf values which increased from 60000 GHz to 185000 GHz.?2?The effects of Zn substitution at A site on the phase composition and dielectric properties of Mg Ta₂O₆ ceramics were investigated.The results showed that when the amount of Zn substitution is less than 0.6,the Mg O₆ or Ta O₆ octahedron in the lattice structure of Mg Ta₂O₆ ceramics is distorted,but the lattice structure is not changed.In this range,the dielectric constant of ceramics increases from 28 to 31,the Qf values decrease from 185000 GHz to 160000 GHz and the?_f decreases from 53 ppm/?to 50ppm/?.When the amount of Zn substitution is more than 0.6,the lattice structure of Mg Ta₂O₆ ceramics is changed from the tetragonal phase to the Zn Ta₂O₆ orthogonal phase,and the dielectric constant of ceramics increases from 31 to 34,Qf values decreases from 160000 GHz to 70000 GHz,?_f also decreases from 50 ppm/?to 0ppm/?.?3?The effects of Sn/Zr substitution at the B position on the composition and dielectric properties of Mg Ta₂O₆ ceramics were studied.The results showed that when the Sn/Zr substitution amount is less than 0.05,the lattice structure of Mg Ta₂O₆ceramics is not changed.The dielectric constants of Mg Ta₂O₆ ceramics are gradually reduced from 28 to 25,the Qf values are reduced from 185000 GHz to 150000 GHz,and the?_f is reduced from 53 ppm/?to 30 ppm/?.When Sn/Zr substitution amount is in the range of 0.05?0.4,the lattice structure of Mg Ta₂O₆ ceramics is dramatically changed and various phases are formed.The dielectric constants of ceramics are reduced from 25 to 18,Qf values decrease rapidly from 150000 GHz to 80000 GHz,and?_f also decreases rapidly from 30 ppm/?to-60 ppm/?.?4?The effects of A-B synergistic substitution?Ga-Sn or Sn-Sn?on the composition and dielectric properties of Mg Ta₂O₆ ceramics were also studied.The results showed that the lattice structure of Mg Ta₂O₆ ceramics is not changed,but the Mg O₆ or Ta O₆octahedron is distorted when Ga-Sn co-substitution amount is less than 0.2.The dielectric constants of Mg Ta₂O₆ ceramics gradually decrease from 28 to 25,the Qf values decrease from 185000 GHz to 140000 GHz,the?_f decreases from 53 ppm/?to15 ppm/?.When Sn-Sn co-substitution amount is less than 0.2,there are similar structural distortion results with Ga-Sn co-substitution in Mg Ta₂O₆ ceramics.The dielectric constants of Mg Ta₂O₆ ceramics with the increase of Sn-Sn co-substitution are reduced from 28 to 22,the Qf values are rapidly reduced from 185000 GHz to 70000GHz,and?_f decreases rapidly from 53 ppm/?to 5 ppm/?.?5?The influence of A,B substitution and A-B synergistic substitution on the composition and dielectric properties of Mg Ta₂O₆ ceramics were investigated.Among them,the dielectric constant is affected by the crystal phase composition whose changing trend can be predicted by Clausius-Mossotti?C-M?equation;the Qf values are affected by the crystal phase composition,porosity and grain boundary loss,which can be increased by reducing the porosity,and grain boundary loss under the condition of constant crystal phase composition.?_f is affected by Mg?Ta?O₆ octahedron distortion and Mg?Ta?-O covalent bond strength.The greater the distortion degree of Mg?Ta?O₆octahedron,the stronger the change of?_f,and the higher the strength of the octahedron covalent bond,the closer the?_f is to zero.Meanwhile,the microwave dielectric properties of ceramics are predicted based on the resonant polarization model and the relationship between the distortion of ceramic lattice structure and the dielectric properties of ceramics.A new method to predict the dielectric properties of materials is established by replacing infrared reflection spectrum with Raman spectrum,which provides a new way for the study of microwave dielectric ceramics.?6?The dielectric properties of Mg Ta₂O₆ based composite ceramics were studied.The microwave dielectric ceramics with tunable dielectric constant,high Qf values and near-zero?_f were successfully prepared.When Mg Ta₂O₆ and Mg₄Ta₂O₉ are complexed,the two crystal phases do not react,the composite magnesium tantalate microwave dielectric ceramics with excellent properties of?_r=18,Qf=210000 GHz,?_f=0 ppm/?were prepared.When Mg Ta₂O₆ ceramics and Zn₂Si O₄ceramics are complexed,the two crystal phases react and a kind of microwave dielectric ceramic with high Qf values of?_r=14,Qf=129000 GHz,?_f=5.3 ppm/?was prepared.These kinds of multiphase ceramics have the highest Qf and the most profitable application potential.