Synthesis And Thermal Expansion Properties Research Of ZrMgMo₃O₁₂/BaTi₄O₉ And ZrMg_1-xAl_xMo_3-xV_xO₁₂

Since the negative thermal expansion(NTE)materials had been found,they have attracted more and more attentions because of the great application prospect in solving the problem of thermal expansion coefficient matching problems of materials.And NTE materials have been made great progress in the mechanism of thermal shrinkage and the practical applications.Besides,the fabrication of new NTE materials has also been widely studied.Along with the progress of research on NTE materials,its application research becomes more and more important.Nevertheless,there are still many problems need to be addressed in the aspects of application scope and depth,such as the application and popularization of NTE materials.However,if we want to study the application and promotion of materials,besides of the performance of the material itself,we also could composite different materials to combine the good performance or improve poor performance of them.In this work,on the one hand,according to the relationship of coefficient of thermal expansion(CTE)and dielectric performance parameters of microwave dielectric ceramics ?f =-(? + 1/2 ??),we composited ZrMgMo3O12 which had good negative expansion performance and microwave dielectric ceramic BaTi4O9.The preparation,microstructure,structure,thermal expansion properties were studied.In addition,we studied on the thermal expansion performance of ZrMg1-xAlxMo3-xVxO12 by the method of ion substitution,which is a novel thermal expansion material.The results are as follows:(1)ZrMgMo3O12/BaTi4O9 composites were prepared by a solid state sintering method.The results of experiment and analysis showed that the optimum sintering temperature was 873K,and it would bring the other hybrid above 873K The addition of ZrMgMo3O12 influenced the microstructure of BaTi4O9,resulting in the microstructure of the composites as irregular blocks and particulates.The CTE and?f of BaTi4O9/ZrMgMo3O12 decreased with the content of ZrMgMo3O12 increasing.When content of ZrMgMo3O12 reached 50%,the CTE would be 2.68×10-6/K,which is only 33%of that of BaTi4O9 and its ?f is-4.29×10-6/K.(2)The changes in dielectric properties of composite samples can be mainly attributed to the changes of microstructure,which caused complex polarization mechanism and density changes.And if regulated by the CTE was greater than the temperature coefficient of dielectric constant(??)owing to the formula of ?f =-(?+1/2??).(3)ZrMgi-xAlxMo3-xVxO12(x=0.2,0.3,0.5,0.6,0.7,0.8)samples had been prepared by a solid state sintering method.The results of the experiments and analysis show that the ZrMgi-xAlxMo3-xVxO12(x=0.3,0.6,0.7)exhibit the NTE properties when the temperature in the range 279-300K,273-313K and 273-320K,respectively.The CTE of the ZrMg1-xAlxMo3-xVxO12(x=0.3,0.6,0.7)are-2.58×10-6/K,-3.18×10-6/K and-3.81×10-6/K respectively.The spatial structure of the samples is still orthogonal structure at room temperature.Moreover,ZrMgi-xAlxMo3-xVxO12(x=0.2)belongs to the orthogonal crystal system and its space group is Pmmn.And its crystal cell parameters are a=13.08811 A,b=9.51821 A and c=9.42391A respectively.The microstructure consists of global,polyhedral and rod-like particulates,which have the sizes of 2-6 ?m and ZrMgi-xAlxMo3-xVxO12 possess better compactness than ZrMgMo3O12.