Microwave dielectric properties of 0.2SrTiO3-0.8Ca0.61Nd0.26Ti1−xAl4x/3O3 ceramics

The phase structure, microstructure and the dielectric properties of 0.2SrTiO3-0.8Ca0.61Nd0.26Ti1−xAl4x/3O3 (0.2 ≤ x ≤ 0.5) ceramics sintered at 1420–1580 °C with conventional solid-state route had been investigated. It was found that the orthorhombic perovskite phase with a small amount of unknown second phase was obtained in the compositional range of 0.2 ≤ x ≤ 0.5. Partial substitution of Ca2+ and Nd3+ by Sr2+ on the A site resulted in a slight increase in the dielectric constant (ɛr) for Ca0.61Nd0.26Ti1−xAl4x/3O3 ceramics. With an increasing of x, the interchange of Ti4+ and Al3+ on the B site caused the increase in quality factor (Q·f). Moreover the temperature coefficient of the resonant frequency (τf) gradually reduced to close to zero with a rise of x from 0.2 to 0.5. And the variation of the τf values with the change of tolerance factor (t) and oxygen octahedral distortion (Δ) was discussed as well. An optimized microwave dielectric properties with ɛr ∼ 48.3, Q·f ∼ 40,700 GHz (at 4.98 GHz) and τf ∼ 3.6 ppm/°C could be obtained as x = 0.5 after being sintered at 1520 °C for 4 h.