Preparation And Properties Of SrTiO₃-based Microwave Dielectric Ceramics

With the rapid development of microwave communication technology,microwave medium components are developing towards miniaturization,low power consumption and high stability.Microwave dielectric ceramics with high dielectric constant,low dielectric loss and excellent temperature stability are urgently needed.Strontium titanate?SrTiO₃?,as a kind of microwave dielectric ceramics,exhibits relatively high dielectric constant?>300?.However,the lower quality factor and poor temperature stability severely limit its application.In this article,B-site and A-site doping and system compounding were carried out by traditional solid-state method based on SrTiO₃.The microstructure and morphology of ceramics were studied in detail.The relationship between phase composition,crystal structure,chemical bond characteristics and properties of ceramics was established.The influence mechanism of microwave dielectric properties of SrTiO₃-based ceramics was analyzed.A series of highperformance microwave dielectric ceramics were developed.Firstly,in order to reduce the dielectric loss of SrTiO₃ ceramics,B-site donor and acceptor doping were implemented by utilizing(Al_0.5Nb_0.5)⁴⁺with a similar radius to that of Ti⁴⁺ions.The effects of doping on the structure were investigated by characterization of crystal structure and microstructure.By analyzing the defect equation and leakage loss,the relationship between grain size and microwave dielectric properties was established,and the changing mechanism of quality factor and leakage current was analyzed.SrTi_0.9(Al_0.5Nb_0.5)_0.1O₃ ceramics with optimum dielectric properties were prepared sintered at 1350?:?_r=185,Qf=9077 GHz?@2.9 GHz?and?_f=587 ppm/?.The Qf value of SrTiO₃ microwave dielectric ceramics was increased by twice while the relatively high?_r was maintained.Secondly,in order to adjust the temperature coefficient of resonance frequency of SrTiO₃ ceramics,A-site donor doping was carried out by using La³⁺ions with a similar radius to that of Sr²⁺ions.The phase transition and A-site ordering degree were analyzed by characterizing the phase composition and microstructure.The correlation mechanism between lattice restoring force and microwave dielectric properties was established based on the calculation of B-O bond length and B-site bond valence.SrTi_0.9(Al_0.5Nb_0.5)_0.1O₃ with optimum dielectric properties were prepared sintered at1350?:?_r=89.3,Qf=15243 GHz?@4.3 GHz?and?_f=160 ppm/?,and the?_f value was reduced by one order of magnitude compared with SrTiO₃ microwave dielectric ceramics?1600ppm/??.Lastly,in order to optimize the microwave dielectric properties of Sr_0.055La_0.63TiO₃,LaAlO₃ with negative?_f values was combined with the ceramics.The mechanism between the microwave dielectric properties and components was identified by the phase analysis of composite system.The relationship between composition and microwave dielectric properties was established by calculating the theoretical results of?_r and?_f.0.9Sr_0.055La_0.63TiO₃-0.1LaAlO₃ systems with optimum dielectric properties were prepared sintered at 1350??_r=77.3,Qf=16577 GHz?@4.4 GHz?,?_f=98 ppm/?.The composite systems maintained high dielectric constant and quality factor,and the?_f value of Sr_0.055La_0.63TiO₃ microwave dielectric ceramics was further suppressed.