Research And Modification On The Dielectric Properties Of TiO₂-based Microwave Dielectric Ceramics

High sintering temperature(1500°C) and large temperature coefficient of resonant frequency(465 ppm/°C) seriously hindered the practical application and development of Ti O2 microwave dielectric ceramics as microwave components. In this paper, with the purpose of lowering the sintering temperature of Ti O2 microwave dielectric ceramic and improving its dielectric properties, we put forward the general rules for the design and modify of dielectric performance to regulate the dielectric properties of Ti O2 microwave dielectric ceramic.Firstly, the effects of nano Cu O on the sintering characteristics and dielectric properties of Ti O2 microwave dielectric ceramics were investigated. Nano Cu O significantly lowered the sintering temperature of Ti O2 microwave dielectric ceramics to 950°C. With 1wt% nano Cu O was added, sintered at 950°C for 2h, the Ti O2 microwave dielectric ceramics had the following dielectric properties: εr=106,Q×f=24808,?f =371 ppm/°C. On this basis, it was found that the Q×f value of Ti O2 microwave dielectric ceramics doped with 1wt% nano Cu O was much higher than that doped with 1 wt% micron Cu O prepared under the same process conditions. There were two reasons for this phenomenon. First, the characteristics of nano Cu O greatly improved the sintering behavior of Ti O2 microwave dielectric ceramics. Second, compared to the micron Cu O, the addition of nano Cu O led to a less extent of lattice disorder and the Ti O2 microwave dielectric ceramic had relative high crystal symmetry, as a result, the intrinsic loss of the Ti O2 microwave dielectric ceramic doped with nano Cu O was lower.Then, the 0.9Ti O2-0.1Li1/2Nd1/2Ti O3-1wt%Cu O microwave dielectric ceramics were prepared by the solid state reaction method. It was found that the temperature coefficient of resonant frequency(?f) of the Ti O2 microwave dielectric ceramic was significantly decreased, but the Q×f values were also seriously deteriorated due to the existence of the new impurity and sintering defects. Therefore, the dielectric properties of Ti O2 microwave dielectric ceramics weren’t effectively improved by this method.Finally, the method of ion substitution was used to decrease the ?f of Ti O2 microwave dielectric ceramics. With the substitution of(Ni1/3Nb2/3)4+ for Ti4+, the(Ni1/3Nb2/3)1-xTixO2(0.3≤x≤0.5) microwave dielectric ceramics were prepared and they did possess good dielectric properties. For example, when x=0.5, that is, when the chemical composition was 9Ti O2-7Ni Nb2O6, the microwave dielectric ceramics had quite good comprehensive dielectric properties: εr=80.7,Q×f=11745,?f=185ppm/°C, which meant that the dielectric properties of Ti O2 microwave dielectric ceramics were successfully improved. Moreover, we also investigated the crystal structure, lattice vibration mode of the(Ni1/3Nb2/3)1-xTixO2(0.3≤x≤0.5) microwave dielectric ceramics, and established reasonable relationship between the structure and its microwave properties.