Tunable rattling effect and microwave dielectric properties in orthorhombic AEu2O4 (A = Sr, Ba) ceramics for dielectric resonator antennas

Abstract

The challenges of achieving high efficiency, high frequency, high selectivity, and low delay in dielectric resonator antennas are critical for 5 G/6 G communications. Therefore, adjusting the strength of the rattling effect emerges as a primary factor governing the overall microwave dielectric polarization and loss in these materials. In this work, AEu<inf>2</inf>O<inf>4</inf> (A = Sr, Ba) ceramics with an orthorhombic structure were successfully synthesized by solid-phase sintering method. SrEu<inf>2</inf>O<inf>4</inf> (1475 °C) exhibited the microwave dielectric properties of ε<inf>r</inf> = 20.1, Q×f = 28,963 GHz, and a near-zero τ<inf>f</inf> of −9.9 ppm/°C, while BaEu<inf>2</inf>O<inf>4</inf> (1500 °C) demonstrated relatively lower ε<inf>r</inf> and higher Q×f values of 18.4 and 57,994 GHz, respectively, along with a negative τ<inf>f</inf> of −36.3 ppm/°C. Compared with the measured permittivity ε<inf>r</inf>, the theoretical permittivity ε<inf>r(C-M)</inf> (18.0) of SrEu<inf>2</inf>O<inf>4</inf> is underestimated, which is mainly related to the under-bonding of Sr-O and Eu(2)-O. The strong rattling effect of Sr-O and Eu(2)-O is the main reason for obtaining the near-zero τ<inf>f</inf> value in SrEu<inf>2</inf>O<inf>4</inf>, while the mitigated rattling effect of Eu(1)-O in BaEu<inf>2</inf>O<inf>4</inf> results in an increased Q×f value. Meanwhile, Q×f values correlate with lattice energy, electrical properties, covalent bonding, and structural stability. Moreover, a dielectric resonant antenna was designed and simulated with BaEu<inf>2</inf>O<inf>4</inf> to meet the requirements of satellite communication.