Significantly enhanced microwave-millimeterwave properties of cordierite ceramics: Roundness regulation of Si-Al hexagonal ring, analysis of far-infrared reflectance and terahertz time-domain spectroscopy

Ultra-low permittivity (ε_r：4–5) Mg₂Al_4–x(Ge_0.5Mg_0.5)_xSi₅O₁₈ (0.12 ≤ x ≤ 0.28) and Mg₂Al_4–y(Mn_0.5Mg_0.5)_ySi₅O₁₈ (0.1 ≤ y ≤ 0.3) cordierite ceramics were fabricated by solid-state reaction method. The improvement in [(Si₄Al₂)O₁₈] hexahedral ring roundness significantly enhances the quality factor through the substitution of complex ionic pairs of Ge_0.5Mg_0.5/Mn_0.5Mg_0.5 for Al lattice sites in the [(Si₄Al₂)O₁₈] hexahedral ring of these cordierite ceramics. Excellent microwave dielectric performances of Mg₂Al_3.8(Ge_0.5Mg_0.5)_0.2Si₅O₁₈ and Mg₂Al_3.8(Mn_0.5Mg_0.5)_0.2Si₅O₁₈ ceramics sintered at 1400 °C were demonstrated using the Hakki-Coleman resonant method with ε_r = 4.676, Q×f = 186, 503 [email protected] GHz and 199,476 GHz @ 27.434 GHz, τ_f = −20.02 ppm/°C and ε_r = 4.807, Q×f = 101,420 [email protected] GHz and 143,005 GHz @ 27.366 GHz, τ_f = −26.44 ppm/°C, respectively. These results present the potential application of high-quality cordierite in future B5G/6 G millimeter and terahertz communication frequency bands.