Research On Low-temperature Preparation And Doping Modification Of BaTiO₃ Based Ceramics

According to the recent development of temperature stable MLCC Sintered at intermediate temperature, the influences of Bismuth layer compound(CaBi₄Ti₄O₁₅, Bi₄Ti₃O₁₂), rare-earth（La2O₃、CeO₂）, and CaO-B₂O₃-SiO₂（CBS） addition on sintering characteristics and crystal structure, dielectric properties of BaTiO₃（BT） system ceramics were investigated using X-ray diffraction（XRD）,scanning electron microscope （SEM）,differential thermal analysis （DTA）, impedance analyzer. The results are as follows:The effects of CaBi₄Ti₄O₁₅ （CBT） addition on the crystal structure and dielectric properties of BT ceramic were investigated. The results show that the curie point was shifted to a high level, and dielectric properties at high temperature were improved by doping CBT. The best properties can be obtained for 0.5 mol% CBT doped sample. The dielectric constant of 1803 and dielectric loss of 2.76% at room temperature were achieved. The variation of dielectric permittivity for BT ceramic is about -17.30% at -55℃, 121.17% at 125℃. The as-prepared ceramic material is not satisfied with X7R specification. Furthermore, the effects of doping rare-earth oxide on the phase structure, sintering characteristic and dielectric properties were investigated based on BT-CBT system. The results show that the ratio of c/a decreased, the Curie point was shifted to low temperature and dielectric peak broadened with adding La2O₃. However, the ratio of c/a and the Curie temperature remained invariable by adding CeO₂. The BT-CBT ceramic doped with 1.0 mol% La2O₃ and 0.01 mol% CeO₂ has a dielectric constant of 2150, dielectric loss of 1.9%, and volume resistivity of 1.92×1010Ω.cm, respectively. The variation of dielectric permittivity as compared with room temperature was about -14.78 at -55℃and -11.44% at 125℃for 1.0 mol% La2O₃ and 0.01 mol% CeO₂ co-doped BT-CBT ceramic sample. The as-prepared ceramic material is satisfied with EIA X7R specification.The effects of Bi₄Ti₃O₁₂ （BIT） addition on the crystal structure, microstructure, sintering characteristics and dielectric properties of BT ceramic were investigated. The results show that the sintering characteristic of BT ceramics was improved by BIT doping. With the increase of BIT doping amount（≤3.0mol%）, the c/a ratio increase and dielectric constant decrease. Second phase Bi2Ti2O7 appearred for 5.0mol% BIT doped sample, and dielectric property deteriorated. With 3.0mol% BIT doping, the BT ceramic sample sintered at 1250℃possess a better property, a room dielectric constant of 1803 and dielectric loss of 1.52% and volume resistivity of 1.92×1010Ω.cm were achieved, and the variation of dielectric permittivity for BT ceramic is about -17.30% at -55℃, 13.42% at 125℃and -11.53% at 150℃. The ceramic materials have great potential as EIA X8R-type multilayer ceramic capacitors due to the“clock-wise effect”. Further more, the effects of CBS doping on microstructure and dielectric property of BT-BIT were also studied. The results show that CBS doping play an important role on reducing sintering temperature and suppressing Curie peak. And the dielectric constant decreased with increasing CBS content. All of CBS doped BT-BIT ceramic samples are satisfied with X8R. However, 3.0wt% CBS doped BT-BIT is better by considering dielectric constant and dielectric loss. The sample exhibits low sintering temperature （1130℃）, high dielectric constant （1789） ,low dielectric loss（1.15%）, high volume resistivity （9.67×1012）. The variation of dielectric permittivity for 3.0wt% CBS doped BT-BIT ceramic is about -12.10% at -55℃, 6.17% at 125℃, -10.78% at 150℃.The as-prepared ceramic material is satisfied with EIA X8R specification.The effects of BIT addition on the crystal structure, sintering characteristics and dielectric properties of BT-Nb2O5-ZnO （BTNZ） system ceramic were investigated, and the influences of CBS addition on the microstructure and dielectric property of BTNZ systems were investigated by doping CBS based on BIT-BTNZ ceramics satisfying X7R type. The results show that BIT doping didn’t change the crystal of BTNZ ceramics, and no second phases come out. It was found that the ratio of c/a was increased, the internal stress structure was modified, and the Curie point was shifted to high temperature and as well as the dielectric temperature stability of BTNZ was improved with increasing BIT content. The dielectric graph shows obvious“double-hump”effect. A dielectric constant of 1327 and dielectric loss of 2.07% at room temperature for 1.0wt%BIT doped BTNZ ceramic sintered at 1230℃were achieved. The variation of dielectric permittivity for BTNZ ceramic is about -7.95% at -55℃, 0.11% at 125℃by doping 1.0wt% BIT. the as-prepared ceramic material is satisfied with EIA X7R specification. The addition of CBS glass can reduce sintering temperature. The dielectric constant and the variation of dielectric permittivity decreased with the increase of BIT content, which indicates that CBS doping play a role on suppressing dielectric peak. 5.0wt% CBS doped BTNZ-BIT sample is satisfied with EIA X8R. The variation of dielectric permittivity for BT-BIT ceramic is about -9.56% at -55℃, 5.93% at 125℃, -8.59% at 150℃. The sample shows medium dielectric constant （εr=1091）, low dielectric loss （tgδ=1.28%）, high volume resistivity （1.46×1011） and low sintering temperature （1050℃）, therefore, the ceramic material has great potential as BaTiO₃-based X8R multilayer ceramic capacitors at low temperature by optimizing technological condition.