| The X7R performance requirement of EIA(Electronic Iudustries Association) specifies with a stable temperature coefficient of capacitance (TCC) should be within±15%of its 25℃value over—55℃to 125℃. Barium titanate is one of the most excellent dielectric ceramic materials widely used in MLCC (Multilayer Ceramic Capacitor). In recently years, the ceramics with high dielectric constant develop fast because it has flattenε-T curve, small size, and the characteristics of difficult to aging and low price.Some composite oxides have the low eutectic point, when they dope BaTiO3 powders, they can promote liquid phase sintering, enhance densitification, decrease sintering temperature, and improve temperature characteristic of ceramics. In a previous study on the basis of Zn-B-Si-O doping BaTiO3, we prepared dual sintering aids of Li-Ti composite oxides (Li2O-TiO2, abbreviated as LTO) and ternary sintering aids of Li-Ti-Si composite oxides (Li2O-TiO2-SiO2, abbreviated as LTSO) nano-composites sintering aids via sol-gel process, and investigated the effect of sol pH value and calcining temperature on the microstructure and phase composition of sintering aids, and use them dope X7R type BaTiO3 ceramics. Then we prepared the BaTiO3 based ceramics with high dielectric constant and stable temperature characteristic.1. We synthesis LTO and LTSO nano-composite sintering aids, and study the effect of sol pH value, oxides ratio and calcining temperature as factors on dispersibility, powders size and phase composition. When the sol pH value was 3 and the calcining temperature was 600℃, the sintering aids have the best dispersibility and the smallest powders size (about 10 nm); and the optimal experiment condition was sol pH value with 4 and calcining at 550℃, then the powders have the best dispersibility and the smallest powders size (about 10 nm).2. LTO powers as sintering aids, X7R type BaTiO3 based ceramics were prepared by solid method, and studied the effect of ratio ([Li2O]/[TiO2]) on phase composition and dielectric properties of BaTiO3 ceramics. When the ratio of Li2O and TiO2 was 0.5:1, the highest room temperature permittvity reached 4429, the max TCC is—10.4%, which met X7R standard. 3. We studed the effect of content of sintering aids on phase composition, microstructure and dielectric properties. If the content of sintering aids was little, it can not promote densitification sintering of ceramics; however, superfluous sintering aids can produce glass phase, which deteriorated dielectric properties. When BaTiO3 based ceramic sintering at 1240℃, the optimal content of sintering aids was 0.025%(ω), the highest room temperature permittvity reached 4543, the max TCC is only—9.0%, which met X7R standard; sintering temperature enhancing, the permittvity increased, but the sintering temperature was too high, which was not in favor of sintering and permittvity decreased. When BaTiO3 based ceramic sintering at 1260℃, the highest room temperature permittvity reached 5150, the max TCC is—11.6%, which met X7R criterion..4. LTSO powders as sintering aids, X7R type BaTiO3 base ceramics were prepared by solid method. When the ratio of Li2O, TiO2 and SiO2 was 2:1:1, as sintering aids, LTSO nano-composites can decrease sintering temperature, improve densification and dielectric constant of X7R type BaTiO3 ceramics; LTSO doped X7R type BaTiO3, when ceramic sintering at 1260℃and the content of LTSO sintering aids, the highest room temperature permittvity reached 4653.5. When the content of sintering aids was 0.05%(ω), the dielectric properties of ceramics could be also improved via increasing sintering temperature. The results indicated that the effect of sintering temperature on dielectric constant was not obvious when the sintering temperature was higher than 1260℃. Based on an overall consideration of various factors, the optimal sintering temperature was 1280℃, and the mainly performances of BaTiO3 based ceramics satified X7R standared:the highest room temperature permittvity was 5260, and the max TCC was 9.7%...
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