Structural characteristics and microwave dielectric properties of a new Sm2O3-Nd2O3-MgO-CeO2 ceramic system

Sm2O3-Nd2O3-MgO-CeO2 ceramic systems of the form Sm1-xNdx(Mg0.5Ce0.5)O3 (0.0 ≤ x ≤ 1.0) were synthesized by a conventional solid-state reaction method, and the phase structural characteristics, microstructures, sintering behaviors and microwave dielectric properties were investigated systematically. X-ray diffraction analyses revealed that a cubic fluorite-type structure with Fm-3m (225) space group was identified as the main crystalline phase in the composition range of x = 0.0-1.0, while some secondary phases were also detected in all the Sm1-xNdx(Mg0.5Ce0.5)O3 samples. The phase structural characteristics of Sm2O3-Nd2O3-MgO-CeO2 quaternary ceramic systems were significantly affected by a certain amount of Mg2+ ion volatilization, detected by the typical EDS data. Additionally, both an example of EDS analysis in the second phases regions and some details of the diffraction peaks implied that the unknown phases were mainly composed of MgO phase. Furthermore, for the microwave characteristics, the relative permittivity (εr) was closely related to the dense degree and phase compositions, and also, the quality factor (Q × f) had been strongly depended on the compactness and lattice defects in these investigated ceramics. Wherein, after sintering at 1450 °C for 4 h, the x = 0.0 sample demonstrated the excellent microwave dielectric performance: εr ∼16.6, Q × f ∼111,280 GHz (at 7.938 GHz) and τf ∼ −56.7 ppm/°C. These results also indicated that the Ce1-xLnxO2-δ (Ln = Sm and Nd) solid solutions could be a good candidate for dielectric resonators, filters and other microwave electronic device applications.