| Summary: | In this work, Y<sub>2.95</sub>R<sub>0.05</sub>MgAl<sub>3</sub>SiO<sub>12</sub> (R = Yb, Y, Dy, Eu, Sm) microwave single-phase dielectric ceramics were successfully prepared via a conventional ceramic sintering technology by doping a series of rare earth elements (Yb, Y, Dy, Eu, Sm) with different ionic radii for the first time. The effects of A-sites occupied by rare earth elements on the microwave dielectric properties of Y<sub>2.95</sub>R<sub>0.05</sub>MgAl<sub>3</sub>SiO<sub>12</sub> were studied using crystal structure refinement, a scanning electron microscope (SEM), bond valence theory, P-V-L theory, and infrared reflection spectroscopy. It was found that the ionicity of the Y-O bond, the lattice energy, the bond energy, and the bond valance of the Al<sub>(Tet)</sub>-O bond had important effects on the microwave dielectric properties. Particularly, the optimum microwave dielectric properties, <i>ε<sub>r</sub></i> = 9.68, <i>Q</i> × <i>f</i> = 68,866 GHz, and <i>τ<sub>f</sub></i> = −35.8 ppm/°C, were obtained for Y<sub>2.95</sub>Dy<sub>0.05</sub>MgAl<sub>3</sub>SiO<sub>12</sub> when sintered at 1575 °C for 6 h, displaying its potential for 5G communication.
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