MnTi co-doping in Mg2Al4Si5O18 ceramics enhances Q factor and improves temperature stability with a τf value closer to zero

Abstract

Co-doping of ions effectively modulates structures and properties of functional ceramic materials. This study fabricated the Mg₂Al₄Si_5−x(Mn_0.5Ti_0.5)_xO₁₈ (0 ≤ x ≤ 0.16) ceramic via solid-state reaction method and achieved remarkable dielectric properties, with values of ε_r = 4.907, Q × f = 159 681 GHz, and τ_f = −21.075 ppm °C⁻¹. The intricate connection between microwave dielectric characteristics and crystalline framework received comprehensive examination through the lens of the complex chemical bond theory. The dielectric constant (ε_r) of Mg₂Al₄Si_5−x(Mn_0.5Ti_0.5)_xO₁₈ (0 ≤ x ≤ 0.16) ceramics primarily depends on material density, bond ionization, and ionic polarization capacity. The quality factor (Q × f) rose 2.24-fold due principally to enhanced lattice energy, with this Q × f value also correlating to the symmetry of [Si₄Al₂] and [O₆] hexagonal rings within the pyroxene crystal structure. The temperature coefficient of the resonant frequency (τ_f) is mainly attributed to the bond energy and deformation of the [MgO₆] octahedra. This study innovatively employs (Mn_0.5Ti_0.5)⁴⁺ to co-dope the Si⁴⁺ sites in Mg₂Al₄Si₅O₁₈ based on ionic radius matching, achieving synergistic optimization of Q × f and τ_f. These findings offer critical guidance for developing silica ceramics featuring elevated Q × f values and near-zero τ_f characteristics for 6G communication systems.