Structural and microwave dielectric properties of the (1−x) Li₃NbO₄−x Ca_0.8Sr_0.2TiO₃ thermally stable ceramics

The ceramic system of (1−x) Li₃NbO₄−x Ca_0.8Sr_0.2TiO₃ prepared by solid reaction route has been found to possess excellent dielectric properties. Li₃NbO₄ was combined with Ca_0.8Sr_0.2TiO₃ to obtain a two-phase ceramic system and to achieve a thermally stable material. As x value varied from 0.1 to 0.4, the temperature coefficient of resonate frequency values (τ_f) ranged from +119.1 ppm/°C to −30.7  ppm/°C. At x = 0.2, the 0.8 Li₃NbO₄–0.2 Ca_0.8Sr_0.2TiO₃ ceramic sintered at 1075 °C for 4 h exhibited outstanding microwave dielectric properties with a relative dielectric constant (ε_r) ∼21.7, a quality factor (Q × f) value ∼49,276 GHz (at 6.1 GHz), and a τ_f ∼5.2 ppm/°C, which represented a promising candidate for microwave dielectric applications. Moreover, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were included in our work to help identify and analyze the phase assemblage and the microstructure of the sintered ceramics. - Highlights: • (1−x) Li₃NbO₄−x Ca_0.8Sr_0.2TiO₃ ceramics were prepared by mixed oxide route. • The τ_f of Li₃NbO₄ was modified to near 0 ppm/°C by incorporating Ca_0.8Sr_0.2TiO₃. • The excellent dielectric properties of ε_r = 21.7, Q × f = 49,276 GHz were achieved. • The optimized sintering temperature of the ceramics was 1075 °C.