The Research Of LaAlO₃-SrTiO₃ Microwave Dielectric Ceramic

With the rapid development of modern communication technology and higher requirement for all kinds of communication equipments, it demands that the microwave dielectric ceramicmaterials widely used in communication components should have a higher performance.LaAlO3 ceramic is a kind of typical middle εr, middle Q×f value microwave dielectric ceramic material with excellent dielectric properties. However, monocrystal LaA103 ceramics remain problems such as low εr, negative τy, high sintering temperature, narrow sintering temperature range and so on, which limit popularization and applicationin industry. Therefore, this paper aiming at low εr and negative τf and in order to find the best composition and process, reduce the sintering temperature and optimize microwave dielectric properties of the material, SrTiO3 and LaAlO3 were mixed with determined ratio and doped with Pr6O11 Nd2O3, MnC03 to discuss the influence of doping amounts on the microstructure and microwave dielectric properties basing on the analysis of the microstructure of LaA103 monocrystal in the paper.Firstly, analytical pure raw material La2O3, Al2O3, SrCO3, TiO2 were mixed with stoichiometric ratio to synthesize LaAlO3 and SrTiO3clinkers respectively and the optimalcalcining process were determine:LaAlO3 was calcined at 1200℃ and held 10h;SrTiO3 was calcined at 1150 ℃ and held 6h.The microwave dielectric ceramics of xLaAlO3-(1-x)SrTi03 doped by 0.5wt%Pr6O11 were prepared by mixing LaA103 and SrTiO3 clinker with solid phase method. The results show that xLaA103-(1-x)SrTi03 form solid solution with perovskite structure. The τf of the material moved along the negative direction, er decline and Qxf value increase first and then decrease with the increase of LaA103 contents; When x=50.82wt%, τf of the ceramics samples sintered at 1600℃ is nearlist close to zero and it have the optimal microwave dielectric properties of εr=37.81, Q×f=36165GHz and τf=0.56ppm/℃.However, Q×f value of the material needs to be improved furthermore. Therefore, 50.82 wt%LaA103-49.18wt%SrTiO3 was doped with different content of Pr6O11 in order to analysis the influence of the doping amount on its structure and properties. The results show that under the high temperature, Pr6O11 decomposed into Pr2O3 and O2 and Pr3+have an A substitution of La3+ to form (Pr, La) AlO3 substitutional solid solution causing the lattice distortion and thereby reducing the sintering temperature of the material. O2 released can filleffectively in oxygen vacancy of system in sintering process and decrease internal defects of the material. With the increase of Pr6O11 doping amount, εr of the material fell slightly, Q x f value increased firstly and then decreased and τf deviate to positive direction.When the Pr6O11 doping amount is lwt%, the ceramic sintered at 1580℃ have the optimal comprehensive microwave dielectric properties of εr= 37.25,Q×f= 42300 GHz and τf= 0.92ppm/℃.In order to reduce the sintering temperature of the material furthermore, 50.82wt%LaAlO3-49.18wt%SrTiO3 was doped Nd2O3 and analysis the influence of doping amount on structure and properties were analysized. The results show that Nd3+ has A substitute of La3+ by doping Nd2O3 and (La,Nd)AlO3 solid solution was formed. The sintering temperature can be reduce effectively, the system εr increases first and then decreases, Qxf value declines witha certain degree, and τf deviate to positive direction. When Nd2O3 doping amount is 3 wt%, the ceramics sintered at 1560 ℃ with holding 6h have the best microwave dielectric properties of εr= 37.72, Q×f=41900 GHz and τf=0.5 ppm/℃.In addition,50.82wt%LaAlO3-49.18wt% SrTiO3 was doped with MnC03 and the influence of doping amount on the structure and properties was analysized in order to bind weak bound electron coming from the LAST ceramic under the high temperature and improve the material Q×f value furthermore. The results show that, doping MnCO3 can bind effectively the weakly bound electron coming from the system and maintain the balance between the Ti3+and Ti4+in the system. But adding excessive MnC03 can lead to the expansion of the cell. When MnCO3 doping amount is 0.3wt%, the material have optimal comprehensive dielectric properties of εr=40.56、Q×f=43500GHz and τf=5.1ppm/℃.