Crystal structure, microwave dielectric properties and antenna simulation of low-permittivity Eu2CaMGa4O12(M = Ti, Sn, Zr) garnets

Abstract

The rattling of cations plays a vital role in energy loss mechanisms and is a fundamental approach for tuning dielectric performance. In this work, phase-pure garnets with the general formula Eu<inf>2</inf>CaMGa<inf>4</inf>O<inf>12</inf> (M = Ti, Sn, Zr) were successfully synthesized. The Eu<inf>2</inf>CaZrGa<inf>4</inf>O<inf>12</inf>, Eu<inf>2</inf>CaSnGa<inf>4</inf>O<inf>12</inf>, and Eu<inf>2</inf>CaTiGa<inf>4</inf>O<inf>12</inf> ceramics were obtained through sintering at 1400°C–1500°C for 6 h. The ceramics sintered at 1450°C exhibited favorable microwave dielectric performance with low ε<inf>r</inf> values of 10.74 (for Sn), 12.34 (for Zr) and 13.66 (for Ti), high Q×f values of 83,500 GHz (for Sn), 72,800 GHz (for Zr) and 59,200 GHz (for Ti), as well as negative τ<inf>f</inf> values of −60.60 ppm/°C (for Sn), −57.20 ppm/°C (for Zr) and −48.20 ppm/°C (for Ti). In Eu<inf>2</inf>CaMGa<inf>4</inf>O<inf>12</inf> (M = Ti, Sn, Zr) ceramics, the “rattling” effect of Eu³⁺and Ga³⁺dominated a slight overall structural expansion, which, in turn, led to the higher ε<inf>r</inf> compared to the theoretical prediction (ε<inf>r(C-M)</inf>) and contributed to the negative τ<inf>f</inf>. The variation in the Q × f values of the ceramics exhibited a negative correlation with the FWHM of the A<inf>1g</inf> Raman mode. Furthermore, due to the ultra-low loss of Eu<inf>2</inf>CaSnGa<inf>4</inf>O<inf>12</inf> ceramic, a dielectric resonator antenna was designed. This demonstrates the promising potential of the ceramics for 5G communication applications.