Preparation And Study Of Performance For RETaO₄ Microwave Dielectric Ceramics

With the development of modern electronic and communication systems,as a new electronic materials,microwave dielectric ceramics(MWDCs)have been broadly applied to daily life because of the proper dielectric constant,low dielectric loss and near-zero temperature coefficient of resonant frequency.At present,most study focus on the serialized permittivity and low dielectric loss.However,in practical application,a nearzero τf can broaden the operating temperature zone of the device greatly,and keep a great property in a wide temperature field.Therefore,this thesis chooses the intermediary electrical constant RETaO4 ceramics as the research object,and the relationship between microwave dielectric properties and crystal structure have been studied systematacially.And two excellent RETaO4 ceramics with a neao-zero τf were obtained.The detailed research are as follows:Among all the RETaO4 ceramics,the rare-earth element La,Er,Dy,Nd,Sm,Ho,Yb,Gd and Ce were chosen for further study.Then the RETaO4 ceramics mentioned above were obtained through the traditional solid state sintered method.The phase composition,microstructure and microwave dielectric properties were studied.The results show that ErTaO4,DyTaO4,GdTaO4,YbTaO4 with stable structure have been prepared,meanwhile,the microwave dielectric properties of these ceramics mentioned above are quite well.Then,YbTaO4 ceramics was chosen to studied further because of the near-zero τf value.Then,the phase composition,microstructure and microwave dielectric properties of YbTaO4 ceramics were studied.With the increasing of the sintering temperature,no more other phase can be found.After the refine of the XRD of YbTaO4 ceramics.The relationship between microscopic crystal structure and microwave dielectric properties was studied by the results of Rietveld and the complex chemical bond theory:the εr,Q ×f,and τf of YbTaO4 ceramics were related to the bond ionic,lattice energy and bond energy respectly.At the sintering temperature of 1675℃,the best microwave dielectric properties were gained:εr=18.52,Q×f=21928 GHz,τf=1.28 ppm/℃.At last,the effects of Sm3+on HoTaO4 ceramics were studied to adjust the temperature drift to a near-zero value,and the phase composition,microstructure and microwave dielectric properties of composited ceramics were studied.The results show that at the sintering temperature of 1600℃,the Ho0.2Sm0.8TaO4 ceramics gained its best microwave dielectric properties:εr=19.71,Q×f=23451GHz,τf=-1.02 ppm/℃.