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Study on the Lead-free Low Loss Y5P-152 High Voltage Ceramics

Author: ChenYaDong
Tutor: RanJunGuo;ZuoChunHua
School: Sichuan University
Course: Materials Engineering
Keywords: low dielectric loss lead-free ceramics SrTiO3 doping modification technics dielectric properties
CLC: TQ174.75
Type: Master's thesis
Year: 2006
Downloads: 32
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Abstract


Environmental issues are critical for everybody around the world. Usingenvironment-friendly material is of fundamental significance for environmentprotection. Low dielectric loss lead-free ceramics get increasingly more atten-tion due to their environment-friendly properties.By strictly controlling every step in the preparation process and applyin-g analytical techniques such as SEM, the effect of Sr-Bi-Ti ceramics prepar-ation on dielectric properties was studied. Combining different stir grind ti-me and rotational speed, sintering temperature and soaking time, the bestset of parameters was determined. It was found that too long stir grind tim-e or too high rotational speed can not decrease the size of ceramic particlesbut bring more impurities into the ceramic and then worsen its dielectricproperties. On the other hand, too short stir grind time or too low rotationa-1 speed may result in oversized particles. Both sintering temperature and so-aking time have a mutually restricting and supplementary relationship. Highsintering temperture should be combined with a short soaking time whilelow sintering temperature should be combined with a long soaking time. Th-e optimized sintering temperature is between 1190℃~1220℃and the opti-mized soaking time is 2 hours.Futhermore, this thesis studied how the amount of Bi2O3·TiO2 affected the dielectric properties and proposed a mechanism behind this effect. Itwas found that Bi2O3·TiO2 can dramatically increase the dielectric constantof ceramics if it is lower than 10mol%. Higher amount of Bi2O3·TiO2 candecrease the dielectric constant and increase the dielectric loss. Also, by lo-wering the Sr/Ti ratio Bi2O3·TiO2 incorporation can decrease the sintering te-mperature. Doping modification research indicate that mixing small amountof MgTiO3 can make the ceramics structure more tightly, reduce defect, incr-ease the dielectric constant and decrease the variation of dielectric constantagainst temperature. Mixing Dy2O3 and MnO2 can decrease the size of cer-amic particles. Dy2O3 can increase dielectric constant if it’s between 0.6wt%~0.8wt%. MnO2 can reduce the dielectric loss and increase break downvoltage of capacitor materials if its concentration is about 0.3 wt%. Combin-ed doping of Nb2O5, SiO2 between 0.1wt%~0.2wt% can prevent the sizeof ceramic crystals to be too large while lower the variation of dielectricconstant against temperature.Based on a series of experiment on different recipe and preparation tec-hnology, we finally get the ceramics with a dielectic constantεr≥1450,dielectric loss tgδ≤0.15%, break down voltage Eb≥10KV/mm[DC], Eb≥4KV/mm [AC] are prepared, and the temperature dependence of dielectric co-nstant can well satisfy the Y5P specification, [(C-30℃-C25℃</sub>/C25℃, (C85℃-C25℃/C25℃]≤±10%. This result is on the advanced level domestically andwill set up a good starting point for the independent development of a newgeneration of lead-free low loss high voltage ceramic capacitors.

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