• Fei Liu

      Articles written in Bulletin of Materials Science

    • 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.

    • Sintering behaviour and microwave dielectric properties of a new complex perovskite: ($1−x$)(Sr$_{0.3}$Ca$_{0.427}$Nd$_{0.182}$)TiO$_{3−x}$SmAlO$_3$ ceramics

      JING JING QU FEI LIU XING WEI CHANG LAI YUAN XIAN PEI HUANG

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      Structural features and microwave dielectric properties of ($1−x$)(Sr$_{0.3}$Ca$_{0.427}$Nd$_{0.182}$)TiO$_{3−x}SmAlO$_{3}($0.05 \le x \le 0.4$) ceramics were investigated. X-ray diffraction patterns illustrated that solid solutions with the orthorhombic perovskite were shown to be formed in the ranges of $0.05 \le x \le 0.4$. Moreover, the dielectric constant ($\epsilon_r$) of sintered ceramics had a quasi-linear decrease with the increase in SmAlO$_3$ content. A certain amount of Sm and Al substitution for A- and B-sites could substantially improve the quality factor ($Qf$) of the ceramics. Increasing the oxygen octahedral distortion led to a decrease in the temperature coefficient of the resonant frequency ($\tau_f$) from 216.3 to $−$34.8 ppm $^{\circ}$C$^{−1}$. Additionally, optimized microwave dielectric properties can be achieved for the specimens using 0.75(Sr$_{0.3}$Ca$_{0.427}Nd$_{0.182}$)TiO$_3$–0.25SmAlO$_3$ ceramics [$\epsilon_r \sim 58.3$, $Qf \sim 18800$ GHz (at 4.65 GHz) and$\tau_f \sim 2.3$ ppm $^{\circ}$C$^{−1}$] after being sintered at 1500$^{\circ}$C for 4 h.

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