• Changlai Yuan

      Articles written in Bulletin of Materials Science

    • Electrical properties of Ba0.7Bi0.3Fe0.9Sn0.1O3–BaCo$_{0.02}^{II}$ Co$_{0.04}^{III}$Bi0.94O3 thick film thermistors with wide-range adjustable parameters

      Changlai Yuan Yun Yang Ying Luo Ling Yang Guohua Chen Xinyu Liu

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      A novel (1−𝑥)Ba0.7Bi0.3Fe0.9Sn0.1O3-𝑥BaCo$_{0.02}^{II}$ Co$_{0.04}^{III}$Bi0.94O3 (0.2 ≤ 𝑥 ≤ 0.9) negative temperature coefficient (NTC) thick film thermistors with high thermistor constant was prepared by screen printing. The values of room-temperature resistivity, thermistor constant and activation energy of the thick film thermistors, increasing with the addition of Ba0.7Bi0.3Fe0.9Sn0.1O3, are in the range of 35.5 𝛺cm-1.34 M𝛺 cm, 2067–6139 K and 0.177-0.527 eV, respectively. This means that the electrical properties of the thick films are adjustable at a wide range, depending on the compositions. Impedance analysis shows that the magnitude of thick film bulk resistance is mainly attributed to the contribution of grain boundary.

    • Effects of LiF on microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics

      Fei Liu Changlai Yuan Xinyu Liu Jing Jing Qu

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      The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics were investigated. The LiF addition enhanced the sintering temperature of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics from 1200 to 1300°C, because the LiF addition could compensate the evaporation of Li during the sintering process. It was found that the bulk density and dielectric constant (𝜀r) gradually decreased, the quality factor (𝑄f) greatly increased and the temperature coefficient of resonant frequency (𝜏f) shifted to a near-zero value with the increase in LiF addition. Obviously, excess Li addition could efficiently improve the microwave dielectric properties. In addition, 0.25Ca0.8Sr0.2 TiO3–0.75Li0.5Nd0.5TiO3 + 4.0 wt% LiF ceramics sintered at 1350°C for 4 h exhibited good microwave dielectric properties of 𝜀r ∼ 123.4, 𝑄f ∼ 2209 GHz (at 2.43 GHz) and 𝜏f ∼ 12.3 ppm °C–1.

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