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 ≤ x ≤ 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 ≤ x ≤ 0.4. Moreover, the dielectric constant (ε 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 (τ f ) from 216.3 to −34.8 ppm • 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 [ε r ∼ 58.3, Qf ∼ 18800 GHz (at 4.65 GHz) and τ f ∼ 2.3 ppm • C −1 ] after being sintered at 1500 • C for 4 h. Keywords. (Sr 0.3 Ca 0.427 Nd 0.182 )TiO 3 ; SmAlO 3 ; microwave dielectric properties; oxygen octahedral distortion.
The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of 0.25Ca 0.8 Sr 0.2 TiO 3-0.75Li 0.5 Nd 0.5 TiO 3 ceramics were investigated. The LiF addition enhanced the sintering temperature of 0.25Ca 0.8 Sr 0.2 TiO 3-0.75Li 0.5 Nd 0.5 TiO 3 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 (ε r) gradually decreased, the quality factor (Q f) greatly increased and the temperature coefficient of resonant frequency (τ f) 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, 0.25Ca 0.8 Sr 0.2 TiO 3-0.75Li 0.5 Nd 0.5 TiO 3 + 4.0 wt% LiF ceramics sintered at 1350°C for 4 h exhibited good microwave dielectric properties of ε r ~ 123.4, Q f ~ 2209 GHz (at 2.43 GHz) and τ f ~ 12.3 ppm °C-1. Keywords. 0.25Ca 0.8 Sr 0.2 TiO 3-0.75Li 0.5 Nd 0.5 TiO 3 ; microwave dielectric properties; microstructures; LiF.
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