| With the rapid development of communication technology,microwave dielectric ceramics occupy a more and more important position in microwave communication.Microwave components should be miniaturized,integrated and low-cost.Therefore,higher and higher microwave dielectric properties are required.Ca0.61Ln0.26TiO3?Ln=La,CLT?has a high dielectric constant??120?but relative low quality factor?Qf10000GHz?and large temperature coefficient of the resonant frequency(?f800×10-6/°C)while Ln(Mg0.5Ti0.5)O3?Ln=La,Nd,Sm;LnMT?has a high quality factor value?Qf35000GHz?but negative resonant frequency temperature coefficient(?f-65×10-6/°C)and low dielectric constant??25-34?.So,in this work,CLT and LnMT are combined to obtain medium dielectric constant,high Qf value and near zero resonance frequency temperature coefficient.The?1-x?CLT-x LnMT?x=0.30.6,molar ratio?microwave dielectric ceramics were prepared by solid state reaction.The phase composition was determined by XRD and the microstructure was observed by SEM.The effects of LnMT and microwave sintering temperature on the microstructure and microwave dielectric properties of?1-x?CLT-x LnMT ceramics were investigated.Meanwhile,the grain growth kinetics of 0.6CLT-0.4LMT ceramics prepared by conventional sintering and microwave sintering were studied,respectively.The results show that,within the composition range,perovskite structure has been formed in?1-x?CLT-x LnMT ceramics.The relative densitis of?1-x?CLT-x LMT,?1-x?CLT-xNMT and?1-x?CLT-x SMT ceramics are higher than 90.5%,95.2%and95.5%,respectively.The lattice constant and cell volume of?1-x?CLT-x LnMT ceramics increase with the increasing x,i.e.the amount of LnMT.With the increase of x,the dielectric constant of?1-x?CLT-x LnMT ceramics decreases as predicted by mixed rule in parallel;as well as the temperature coefficient of resonance frequency decreases;however,Qf value changes greatly.Some ceramics with good comprehensive microwave dielectric properties were obtained:?=47,Qf=19257GHz?f=7.9×10-6/°C?0.6CLT-0.4LMT?;?=51,Qf=13852GHz,?f=-1.9×10-6/°C?0.65CLT-0.35LMT?;?=53,Qf=12846GHz,?f=1.1×10-6/°C?0.65CLT-0.35SMT?.As to conventional sintering?CS?,with the increase of sintering temperature,the grain growth kinetics index of 0.6CLT-0.4LMT ceramics decreases from 3.24?1550°C?to 2.27?1625°C?;the growth activation energy increases with the extending of holding time.On the other hand,as for microwave sintering?MS?,with the increase of sintering temperature,the grain growth kinetics index of 0.6CLT-0.4LMT ceramics decreases from 3.48?1475°C?to 2.13?1550°C?;the growth energy increases first and then decreases with the increase of holding time.In a word,the growth kinetics index of 0.6CLT-0.4LMT ceramics reduced from 2.99?CS?to 2.64?MS?.The growth activation energy of microwave sintering and conventional sintering is655.29kJ/mol and 889.17kJ/mol respectively.It indicates that the grain growth of0.6CLT-0.4LMT ceramics was promoted significantly during the microwave sintering process,compared with conventional sintering. |
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