The Study of Non-Reducible High Temperature Stable Dielectric Ceramics

• Main Authors: Jian-Hua Li, 李建樺
• Other Authors: 王錫福
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/hgzq5k

博士 === 國立臺北科技大學 === 材料科學與工程研究所 === 107 === This study investigated non-reducible temperature-stable dielectric ceramics that were non-reducible when sintered and had stable dielectric properties at high temperatures (≥150°C). On the basis of the specifications established by the EIA (Electronic Industries Alliance, U.S.A.) for high dielectric constant capacitors (class II), the materials examined in this study were (1) an X8R dielectric ceramic (−55°C–150°C, ΔC25°C ≤ 15%) and (2) an X9R dielectric ceramic (−55°C–200°C, ΔC25°C ≤ 15%). These two dielectric ceramics that could be applied to different temperature ranges were investigated from different perspectives of material design. Their applicability for use on multilayer ceramic capacitors were tested. To examine the non-reducible X8R dielectric ceramic, BaTiO3+0.05 mol% MnCO3+1.37 mol% BaSiO3 was used as a host material to investigate the effects of varying amounts of additives (0.3–0.6 mol% Sc2O3 and 0–2.0 mol% MgO) on the crystal structure and dielectric properties. The analysis results from the transmission electron microscopy revealed that when the content of Sc2O3 doped reached 0.45 mol%, a core-shell structure with a Sc concentration gradient was formed within the BaTiO3 grains, thereby effectively inhibiting the influence of the dielectric constant on temperature change and satisfying the X8R specification. Optimal properties were exhibited when 0.45 mol% Sc2O3 and 1 mol% MgO were doped, which resulted in a dielectric constant of 1744 and dielectric loss of 0.58%. Additionally, the TCC (Temperature Coefficient of Capacitance) was−3.9% at -55°C and −8.5% at 150°C. Favorable insulating properties of 2.8 × 1012 Ω–cm and 1.7 × 1011 Ω–cm were exhibited at the temperatures of 25°C and 150°C, respectively. The non-reducible X9R dielectric ceramic used in this study was a composite dielectric ceramic system (BT-5.26BLT) composed of 94.76 mol% BaTiO3 and 5.26 mol% Ba2LiTa5O15. The effects of various amounts of additives (MnCO3: 0–2 mol%; CaCO3: 0–3 mol%; Li2TiO3: 0–7 mol%; and SiO2: 0-1 mol%) on the crystal structure and dielectric properties of this material system were investigated. X-ray diffraction and scanning electron microscope analyses were conducted to reveal the effects of each additives on the variation of sintered ceramic crystal structures. The results indicated that when components in the sintered ceramic influenced one another and intensified their characteristics, the material’s dielectric temperature properties were stabilized and satisfied the X9R specification. The best composition was determined to be the host material with 5.0% Li2TiO3, 1.5% MnCO3, 2.0% CaCO3 and 1.0% SiO2, which resulted in a dielectric constant of 800 and dielectric loss of 1.4%. Additionally, the TCC was −3.6% at -55°C and −9.2% at 200°C. Favorable insulating properties of 1.2 × 1011 Ω–cm and 7.5 × 109 Ω–cm were exhibited at 25°C and 200°C, respectively.