Microstructures and microwave dielectric properties of (1 − x)(Sr0.4Na0.3La0.3)TiO3–xLnAlO3 (Ln = Sm, Nd) ceramic systems

(1 − x)(Sr0.4Na0.3La0.3)TiO3–xLnAlO3 (Ln = Sm, Nd) (0.25 ≤ x ≤ 0.4) ceramics were prepared through the conventional solid-state route. The X-ray patterns revealed that a single phase with perovskite-like structure was obtained in the range of 0.25 ≤ x ≤ 0.4 for the specimens with SmAlO3. However, a small amount of second phase was detected in the specimens with NdAlO3 at x = 0.4 when the sintering temperature was 1520 °C. The dielectric constant (ɛr) linearly decreased with an increasing of LnAlO3 content due to the smaller dielectric polarizability of LnAlO3 than that of (Sr0.4Na0.3La0.3)TiO3. The quality factor (Q·f) was strongly depended on microstructures of these ceramics. And the temperature coefficient of the resonant frequency (τf) shifted to near zero and negative direction with a rise of x, which resulted from the decrease in atomic bond length. Moreover, the effects of different sintering conditions on dielectric properties were studied for the (1 − x)(Sr0.4Na0.3La0.3)TiO3–xNdAlO3 (x = 0.4) ceramics sintered at 1580 °C. The excellent microwave dielectric properties with a near-zero τf ∼ 1.2 ppm/°C, ɛr ∼ 45.2 and Q·f ∼ 38,000 GHz (at 5.01 GHz) could be obtained for x = 0.4 after being sintered at 1580 °C for 4 h.