| The influence of formulae on the dielectric properties of (1-z) (Ba1-x-ySrxCay)TiO3· z(Bi2O3·3TiO2) series middle-high voltage ceramic capacitors has been investigated by means of orthogonal design experiments. The major and secondary influencing factors and the influencing tendency of various factors' levels for the dielectric properties of this ceramics have been obtained. The order of major and secondary influencing factors is SrTiO3, Bi2O3 -3TiO2 and CaTiO3 for dielectric constant, and Bi2O3-3TiO2, SrTiO3 and CaTiO3 for dielectric losses and CaTiO3 , SrTiO3 and Bi2O3-3TiO2 for breakdown voltage. At the same time, the optimum comprehensive properties formulae (X=0.3, Y=0.1 , Z=0.03) and the formulae for the lowest dielectric constant and the highest breakdown voltage( X=0.4, Y=0.15, Z=0.04) have been obtained in the experimental conditions. The performance of the former ceramic capacitors which was sintering at 1240 ℃ for 60 minutes is ε r=3802, tg δ =0.42% , Eb=9.2 kv/ mm; the latter which was sintering at 1220℃ for 60 minutes is ε r=2089, tg δ =0.06%, Eb=16.9 kv/mm.The influence of the dopants ZnO, ZrO2 and Nb2O5 on the dielectric properties for middle-high voltage ceramic capacitors has also been discussed. It is found that doping ZnO and Nb2O5 can suppress the grain to grow up validly and improve the sintering and microstructure of the capacitor ceramics. It was found that a bit of doping ZnO can sharply increase the breakdown voltage of (1-z)(Ba1-x-ySrxCay)TiO3 · z(Bi2O3·3TiO2) series ceramic capacitors and a bit of doping Nb2O5 can lower the dielectric losses of this kind of material. The multiple dopants ZnO , ZrO2 and Nb2O5 can clearly improve the dielectric properties of the ceramic based on (1-z)(Ba-1x-ySrxCay)TiO3 · z(Bi2O3·3TiO2)for middle-high voltage capacitors . The dielectric properties of 0.98(Ba0.7Sr0.2Ca0.1)TiO3·0.02(Bi2O3·3TiO2) sample doped with ZnO, ZrO2 and Nb2O5 are as follows: εr=3469,tgδ=0.4%, Eb=9.4kv/mm.These properties are obviously higher than those of undoped (ε r= 2108, tgδ=3.1%, Eb=7.4kv/mm) . The influencing mechanism of varlous components on the dielectric properties of this kind of dielectric ceramics has been studied, thus providing the basis for preparation of ceramic capacitors with high dielectric constant, low dielectric losses and high breakdown voltage.The influence of burning system on the properties and structure of the ceramic capacitors has been studied Under the certain temperature system, the optimum sintering temperature of the ceramics was primarily decided by the content of Bi2O3·3TiO2. The sintering temperature dropped with the adding of Bi2O3·3TiO2. At the range of suitable sintering temperature, slow heating and low temperature sintering can obtain fine grain and dense structure .It results in the improving of the breakdown voltage for the middle-high voltage ceramic capacitors.The influence of the synthesizing temperature of BaTiO3 on the dielectric properties has also been studied. The results showed that the optimum synthesizing temperature of BaTiO3 is 1150℃. The ceramic capacitors prepared with the BaTiO3 powder, which was synthesized under this temperature condition, has better dielectric properties.The synthesizing of the powder and the grain phase of the products have been investigated with DTA and X-ray. The synthesizing temperature has also been decided by the analyses results. The influences of the burning system on the microstructure and denseness of the dielectric ceramics have been studied with SEM. Different burning systems lead to different microstructure and denseness, so the dielectric properties is different.
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