The Influence of CuO on Temperature-Dependent Capacitance Characteristics in SrTiO3-PbTiO3-Bi2O3-nTiO2 Ceramics

摘要

As we know, the current oil-immersed or thin film power capacitors used in electronic capacitive voltage transformer (ECVT) have the hidden danger of flammable, explosive, and easy pollution, so it is necessary to find their suitable substitutes in the future. High voltage ceramic capacitors have many advantages such as good electromagnetic compatibility, small volume and high withstand voltage, so it can be used as the voltage dividing capacitor of ECVT. However, the capacitance of the ceramic capacitors will become unstable when the ambient temperature changes, which will cause the fluctuation of the voltage dividing ratio of ECVT and greatly reduce its measurement accuracy. In order to obtain the ceramic capacitors with good temperature stability, a new kind of SrTiO3-PbTiO3-Bi2O3-nTiO2(SPBT) ceramics was prepared by mixed sintering, and the effects of CuO on the capacitance-temperature characteristics and microstructure of SPBT ceramics were investigated. In this study, we first synthesized two sets of SPBT ceramic materials with low and high Curie temperature by equimolar exchange of Sr and Pb elements, then M-SPBT ceramic materials were made by mixing low and high Curie temperature ceramic materials at a ratio of 7:3, finally, the different amounts of CuO were doped into the M-SPBT ceramic materials for good temperature stability. The results show that the sintered M-SPBT ceramics doped with 0.4 wt% CuO obtains the best temperature stability ($Delta mathrm{C}/mathrm{C} < pm 5%$, −45 °C ∼ 85 °C), moreover, its dielectric constant is more than 1000 and dielectric loss is as low as 0.29% at 25 °C, besides, it also obtains the denser microstructure compared with undoped. Furthermore, it is suggested that CuO is an effective additive that can improve the temperature stability of M-SPBT ceramics. When 0.4 wt% CuO is added, Cu^{2+ may occupy Ti4+ site due to their close values of ionic radius, this migration will make the number of strontium vacancies in the lattice of M-SPBT ceramics reduced by electrovalent compensating replacement, so the excessive interdiffusion of Sr2+ and Pb2+ in the sintering process is suppressed, which effect a lot on broadening of Curie peak, the temperature change rate of capacitance and dielectric loss can be decreased accordingly. Thus, owing to its high dielectric constant, lower dielectric loss and flat temperature-dependent capacitance characteristics, this new M-SPBT ceramics will be a promising material for voltage dividing capacitor of ECVT.}