Structural and microwave dielectric properties of temperature-stable Ca1-xEuxMo1-xNbxO4 ceramics for dielectric resonator antenna applications

Abstract

Ca1-xEuxMo1-xNbxO4 (0.1 ≤ x ≤ 0.7) ceramics were synthesized through the co-substitution of Ca2+ and Mo6+ in CaMoO4 using Eu3+ and Nb5+. All samples exhibited tetragonal scheelite structures within the range of 0.1 ≤ x ≤ 0.6. However, at x = 0.7, a monoclinic fergusonite structure was observed, as the [Nb/MoO4] tetrahedron at the B-site transforms into a [Nb/MoO6] octahedron. As the substitution amount increases, εr (11.39–16.40), Q×f (21,950–82,930 GHz), and τf (−47.72 to +8.01 ppm/℃) all show a gradual increase. Notably, the τf value of this system can shift from negative to positive. The structural influence mechanism on the microwave dielectric properties in Ca1-xEuxMo1-xNbxO4 ceramics was clarified through various analytical methods, including ion polarizability, P-V-L chemical bond theory, bond valence theory, density of states (DOS), and electron localization function (ELF). Additionally, a resonant antenna designed and simulated using Ca0.4Eu0.6Mo0.4Nb0.6O4 meets the requirements for satellite communication.