Study On BaTiO₃ Based X7R Materials Of Chip Multilayer Ceramic Capacitors With High Voltage

With the help of the orthogonal design experiment, the single factor variable experiments doped with Bi₄Ti₃O₁₂ and Dy₂O₃, the influence of various components on the dielectric performance,TC characteristic, sintering temperature of barium titanate based high voltage capacitor ceramics with X7R specification has been investigated.The influencing mechanism of various components on the dielectric properties of barium titanate based capacitor ceramics is studied. These provide the basis for preparation of barium titanate based capacitor ceramics with high voltage and X7R specification.The behavior of the capacitor ceramic with high voltage and X7R specification reached the level as follows: the dielectric constant e is 1324.2, dielectric loss is 0.0070,the sample density is 5.9415g·cm^-3, the rate of insulation resistance is 6289.13GΩ·cm,the sintering temperature is 1120℃,ΔC/C do not exceed ±15%, the compression strength is larger than 10kv/mm, the size of crystal grain is about 1μm.Doping CdO helps Nb₂O₅ and Dy₂O₃ dissolve and diffuse, reducing material's sintering temperature effectively, raising dielectric constant ,improving the shape look of crystal grain of ceramics, restraining crystal grain from growing up. Excessive Nb₂O₅ segregates in crystal boundary, preventing crystal boundary from moving, restraining the growth of crystal grain, thus forming close grain structure. Ca²⁺ and Zr⁴⁺ respectively enter into some Ba²⁺ andTi⁴⁺ location in the crystal lattice, reducing the dielectric constant peak value in the curie point, making curie temperature moving towards low temperature, restraining crystal grain growing up ,elevating dielectrical constant.Bi₄Ti₃O₁₂ glass phases parcel crystal grain and are filled with between grains, forming the complex and not even structure of ceramic body. Different phases restricts barium titanate ferroelectric phases, making the depth of potential well of B position cation change shallow. In the broad temperature scope, polarization is easily located by electric field,which show ε-T characteristic curve rather smooth.In barium titanate based ceramic, doping small rare earth oxide Dy₂O₃ can keep back the growth of crystal grain, producing close grain effect, making curie summit in entire work temperature range scatter and spread, get higher dielectric constant andgood capacity temperature property,satisfy X7R property, raising the compression strength of barium titanate based ceramic substantially.Nanometer (Bao.7oSro.25Cdo.o5)Ti03 powder is prepared by a sol-gel method from Ba(CH3COO)2-Sr(NO3)2-Cd(NO3)2-Ti(OC4H9)4-H2O-CH3COOH-CH3CH2OH system. Heat treatment in 950°C can form perovskite structure,which is low 250°C³00°C than traditional solid phase synthesis. The average particle size of the powder body is 70 run , the specific surface area is 16.30m2/g,but have certain level aggregate phenomenon.The (Bao.7oSro.2sCdo.o5)Ti03 ceramics which grain size approximately 1 n m are prepared using (Bao.7oSro.25Cdo.o5)Ti03 namometer powder. The dielectric performance of the sample sintered in 1300°C in 1kHz and 25°C is as follows: dielectrical constant 6=1558.4, dielectric loss tan8=0.0170.The dielectric performance of the sample sintered in 1320"C in 1kHz and 25 "C is as follows: dielectrical constant ï¿¡=2592.4, dielectric loss tan8=0.0185. With decrease of the grain size,the temperature representing the maximum dielectric constant decreases while the maximum dielectric constant increases.