Reseach Of Properties And Microstructures For Al₂O₃-TiO₂ Low Permittivity Microwave Dielectric Ceramics

Al₂O₃-TiO2 low permittivity microwave dielectric ceramics have been studied in this thesis. At beginning, TiO2 is added into Al₂O₃ ceramics to modulate the value ofÏ„f ; in addition, in order to reduce the sintering temperature and improve microstructures as well as dielectric properties, different kinds of additives are studied. Details are as follows:The influence of Nb₂O₅ on microstructures and dielectric properties of 0.9Al₂O₃-0.1TiO2 ceramics have been studied. It is interesting to find that Nb5+ and Al3+ can substitute for Ti2+ and form Ti0.8Al0.1Nb0.1O2,which can reduce the sintering temperature and accelerate sintering speed. It shows that when 0.5%wt Nb₂O₅ is doped into ceramics, sintering temperature can be reduced 150℃and dielectric properties can be improved a lot. After calcining at 1200℃and sintering at 1400℃,εr can reach 10.38,Qf can increase to 15500GHz,whileÏ„f is about 9.6 ppm/℃.SiO2 is the second kind of additives. When added into ceramics, SiO2 can react with Al₂O₃ to form glass phase, which can improve sintering process and reduce the sintering temperature; SiO2 can prevent the formation of Al2TiO5 in some extent, but it will deteriorate dielectric properties. It is shows that when 0.8%wt SiO2 is added into ceramics, sintering temperature can be reduced 100℃.After calcining at 1200℃and sintering at 1450℃,εr is 8.2 ,Qf will fall to 9200GHz,whileÏ„f is about–3.1 ppm/℃.Li3AlB2O6 (LAB) glass of low melting temperature is used to provide glass phase directly, which will exist in the way of liquid phase at higher sintering temperature to improve sintering process. It shows that when 1%wt LAB is added into ceramics, sintering temperature can be reduced 150℃, but the introduction of LAB will lead rich amount of TiO2 on surface and inhomogeneous microstructure. After calcining at 1200℃and sintering at 1450℃,εr can reach 10.3,Qf can increase to 14500GHz,whileÏ„f is about 15.6 ppm/℃.