Study on Ba0.7Sr0.3TiO3 Series Capacitor Ceramics with High Dielectric Constant and Low Temperature Changing Rate of Relative Permittivity

Study on Ba0.7Sr0.3TiO3 Series Capacitor Ceramics with High Dielectric Constant and Low Temperature Changing Rate of Relative Permittivity
　　In this article the barium-strontium titante preparation techniques in recent yearshave been summarized. The results of rare-earth oxide(such as Dy2O3、CeO2、La2O3、Y2O3 and Yb2O3 etc.), and the additions of MgO、Bi4Ti3O12 and Bi2Sn2O7 on dielectricproperties and microstructure are studied. The results show that the samples with highdensity, low pore rate and close homogeneous grain possess the high electric breakdownstrength and suited for X7R character. The Block neodymium magnet influences of technological parameter on theceramic properties have been investigated. Moreover, with the aids of SEM and XRD,the samples are analysed, and the results are used to discuss the machanism ofimproving characteristics.The following experiment results have been achieved:In barium-strontium titanate based ceramic, doping small rare earth oxide Dy2O3and Y2O3 can keep back the growth of crystal grain, producing close grain effect,making curie summit in entire work temperature range scatter and spread, get higherdielectric constant and good capacity temperature property, raising the compressionstrength of barium-strontium titanate based ceramic substantially.
　　When the content ofY in barium-strontium titanate ceramics is O.6wt% sintering at 1250℃, relativedielectric constant is more than 4000; from-25 up to 80℃, the change of temperaturedependence of relative permittivity is less than 20%; electric breakdown strength E ismore than 6kV/mm.In barium-strontium titanate based ceramic, doping small rare earth oxide CeO2and La2O3 can inhibit the grain growth and reduce the size of grain, and the dielectricperprities of barium-strontium titanate ceramics can be improved by adding properamount of La3+ and Ce4+ dopants. But replacement mechanism of Ce4+ and La3+ forbarium-strontium titanate is different. Dielectric perproties of Ce-doped BST ceramicsis better than that of La-doped. When the content of Ce4+ in barium-strontium titanateceramics is O.9wt% sintering at 1250℃, relative dielectric constant is more than 3000;from-25 up to 80℃, the change of temperature dependence of relative permittivity isless than 35%; electric breakdown strength E is more than 4kV/mm.X-ray diffraction analysis shows that the crystal structure of barium- http://www.chinamagnets.biz/  strontiumtitanate ceramics is not affected by Yb-doping. With the increase of sinteringtemperature, the dielectric constants of barium-strontium titanate ceramics becomeelevation.
　　When the content of Yb3+ in barium-strontium titanate ceramics is 0.9wt% sintering at 1250℃, relative dielectric constant is more than 10000; electric breakdownstrength E is more than 7kV/mm.The temperature dependence of dielectric constant is depressed and broadens withMgO doped. And XRD paterns show a single perovskite phase on samples. When thecontent of Mg2+ in barium-strontium titanate ceramics is 0.2wt% sintering at 1250℃,relative dielectric constant is more than 4500; from-25 up to 80℃, the change oftemperature dependence of relative permittivity is less than 25%; electric breakdownstrength E is more than 6.5kV/mm.The results show that Bi4Ti3O12 and Bi2Sn2O7 parcel crystal grain and are filledwith between grains, forming the complex and not even structure of ceramic body.Different phases restricts barium-strontium titanate ferroelectric phases, making thedepth of potential well of B position cation change shallow. In the broad temperaturescope, polarization is easily located by electric field, which showε-T characteristiccurve rather smooth. When the content of Bi2Sn2O7 in barium-strontium titanateceramics is 30wt% sintering at 1150℃, relative dielectric constant is more than 1500;from-55 up to 125℃, the change of temperature dependence of relative permittivity isless than 15%. Block neodymium magnet The results of Ba/Sr ratio on dielectric properties and microstructure are studied.The results show the optimized matching of Ba/Sr ratio is very important to dielectricperproties of BST ceramics.A kind of perfect ceramic material for capacitors is obtained by the selections ofdopants and processing. Its main electrical performances are:ε≥3500; tgδ≤0.01; from-25 up to 80℃, the change of temperature dependence of relative permittivity is lessthan 15%; electric breakdown strength E is more than 5.5kV/mm.