Crystal structure and dielectric properties of a new Na2O-Nd2O3-CeO2 ceramic system at microwave frequencies

Abstract

Na2O-Nd2O3-CeO2 ceramic systems of the form Na3x−1Nd1−xCeO3 (x=0.4, 0.5, and 0.6) were prepared via a solid-state reaction method. X-ray diffraction analyses indicated that the samples with x=0.4, 0.6 and those with x=0.5 formed Nd0.25Ce0.75O1.875 and Nd0.5Ce0.5O1.75 solid solutions, respectively, which resulted from a large degree of Na+ ion evaporation. Both the Nd0.25Ce0.75O1.875 and Nd0.5Ce0.5O1.75 phases belonged to the same cubic structure with an Fm-3m (225) space group. Additionally, the microstructures, sintering behaviors, and microwave dielectric properties were considered to be strongly related to the Na content in the Na3x−1Nd1−xCeO3 ceramics. A relatively large degree of Na+ ion evaporation could increase the negative temperature coefficient of the resonant frequency (τf) for these ceramic systems. Moreover, after sintering at 1380°C for 2h, the x=0.6 specimen possessed a low permittivity (εr) of approximately 9.13, a moderate quality factor (Q×f) of approximately 23,800GHz (at 9.14GHz) and a negative τf value of approximately −61.7ppm/°C. As a result, it could be a promising microwave dielectric material for achieving a near-zero τf value by solidifying one or more microwave dielectric ceramics with a high positive τf value.