| MgZrNb2O8 ceramics attracted wide attention due to their good microwave dielectric properties.In this thesis,MgZrNb2O8 ceramics were synthesized through conventional solid-state process and analysed the effect of different ions substitution on lattice structure and microwave dielectric properties,and investigated the internal factor influencing the microwave dielectric properties of ceramics samples.Analysed the effect of Ta5+substitution on lattice structure and microwave dielectric properties.The Ta5+substituted ceramics samples have a higher sintering temperature of 1300oC.With the increase of Ta5+substitution amount,the unit cell decreased,the dielectric constant?r decreased,the quality factor Q×f increased and the temperature coefficient of resonant frequency?f decreased.Analysed the effect of Sn4+substitution on lattice structure and microwave dielectric properties.At the sintering temperature of 1260oC,ceramics samples demonstrated high density and pure phase.With the increase of Sn4+substitution amount,unit cell volume decreased,?r decreased,Q×f increased and?f decreased.Analysed the effect of A-site Ni2+and Co2+ions substitution on lattice structure and microwave dielectric properties.Due to the different ionic radii of Ni2+and Co2+,the unit cell volume and microwave dielectric properties also show different change trend.When the substitution amount of Ni2+is 0.08,ceramics samples have the best microwave dielectric properties:?r=24.58,Q×f=74534.1GHz,?f=-49.11ppm/oC;When the substitution amount of Co2+is 0.02,ceramics samples have the best microwave dielectric properties:?r=25.18,Q×f=70709GHz,?f=-46.09ppm/oC.Based on MgZr0.85Sn0.15Nb2O8 with optimal microwave dielectric properties,analysed the change of crystal structure and microwave dielectric properties of MgZr0.85Sn0.15Nb2O8 ceramics with the increase of sintering temperature.The increase of sintering temperature caused the unit cell volume of ceramics samples decreased first and then increased.It also induced the change of microwave dielectric properties:the dielectric constant?r increased,the quality factor Q×f increased first and then decreased,the temperature coefficient of resonant frequency?f rised first and then falled.Analysed the internal factor influencing the microwave dielectric properties:dielectric constant is related to bond ionicity and ions polarizability,quality factor is related to lattice energy and packing fraction,temperature coefficient of resonant frequency is related to bond energy and bond valence. |
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