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Mg2SiO4 and MgSiO3 ceramics with superior microwave dielectric properties are considered to be promising candidates for 5G applications. However, a slight deviation from the stoichiometric Mg/Si ratio will significantly influence their microwave dielectric properties, which will hinder their practical applications. In this work, the xMgO-SiO2 (x = 1~2) ceramics were synthesized by a solid-state reaction method. The influence of the Mg/Si ratio x on the crystalline phase, microstructure, and microwave dielectric properties was investigated through X-ray diffraction (XRD), a scanning electron microscope (SEM), and the resonant cavity method. The XRD patterns revealed the coexistence of Mg2SiO4 and MgSiO3 within the x range of 1~2, which was further demonstrated by the energy-dispersive X-ray spectra. The SEM images show a typical polycrystalline morphology of ceramics with an inhomogeneous grain size distribution. It is found that the microwave dielectric properties fluctuate at both sides of the x range while those remain relatively stable with minor changes at the intermediate components, indicating an obvious low composition dependence helpful for practical applications. Further, a demonstrator of a microstrip patch antenna for 5G applications using the 1.5MgO-SiO2 ceramic was designed and fabricated, and a return loss of −16.2 dB was demonstrated, which demonstrated the potential applications. [ABSTRACT FROM AUTHOR]

In this study, high-entropy Mg 1.8 R 0.2 Al 4 Si 5 O 18 (R Ni, Ni 1/2 Co 1/2 , Ni 1/3 Co 1/3 Zn 1/3 , Ni 1/4 Co 1/4 Zn 1/4 Cu 1/4 , Ni 1/5 Co 1/5 Zn 1/5 Cu 1/5 Mn 1/5) cordierite ceramics based on equimolar ratios were designed and synthesized through the solid-state reaction technique at high temperatures. The effect of various R-ionic substitutions at the octahedral site and their relationship with ionic polarization, chemical bonding, and configurational entropy were explored. These factors have greatly affected the microwave dielectric properties of Mg 1.8 R 0.2 Al 4 Si 5 O 18 ceramics. The presence of cation radius mismatch and electronegativity mismatch at [MgO 6 ]-octahedron lattice sites revealed lattice distortion resulting from multiple cation substitutions. As the entropy values increased, the temperature stability of microwave dielectric properties of Mg 1.8 R 0.2 Al 4 Si 5 O 18 ceramics improved. For R Ni 1/2 Co 1/2 , a higher Q×f of approximately 73,658 GHz @ 13 GHz, with ɛ r ∼4.44 and τ f ∼ −23.9 ppm/°C was obtained. In the case of R Ni 1/5 Co 1/5 Zn 1/5 Cu 1/5 Mn 1/5 , a near zero τ f (−10.7 ppm/°C), ɛ r = 4.68 and Q×f = 35,478 GHz @13 GHz were achieved, making it potentially suitable for practical applications. [ABSTRACT FROM AUTHOR]

In garnet phase ceramics Y 2.9 M 0.1 Al 4.9 Si 0.1 O 12 (M = Mg2+, Co2+, Zn2+, Mn2+, Ca2+, Sr2+, Ba2+), rattling effects occur when M = Mg2+, Co2+, Zn2+, Mn2+ ions with smaller ionic radius (<1Å) occupy the dodecahedron lattice lattices. This results in an abnormally high dielectric constant, in contrast to the larger ionic radius (>1 Å) of M = Ca2+, Sr2+ and Ba2+, which deviate from the theoretical values calculated using the Clausius-Mosotti formula according to each ion's polarizability. The optimal microwave dielectric properties for Y 2.9 Mg 0.1 Al 4.9 Si 0.1 O 12 was obtained by sintering at 1575 °C for 5 h (Q × f = 51,382 GHz, ε r = 9.74, and τ f = −30.12 ppm/°C). Additionally, a thermal stable Y 2.9 Mg 0.1 Al 4.9 Si 0.1 O 12 -6 wt%TiO 2 composite ceramic was developed. Based on this composite, a Wifi6E/7 patch antenna operating at 6.3 GHz and a millimeter-wave resonant antenna functioning at 27.1 GHz were designed and validated. This indicates the potential application prospects of garnet ceramics in 5G/6G radio communication technologies. [ABSTRACT FROM AUTHOR]