Bond characteristics and microwave dielectric properties of (Li0.5Ga0.5)2+ doped Mg2Al4Si5O18 ceramics

Abstract Cordierite ceramic is one kind of important electronic materials for radio frequency circuit. In this work, Mg2-x (Li0.5Ga0.5)xAl4Si5O18 (0 ≤ x ≤ 0.1) ceramics with pure cordierite phase, were successfully synthesized via the traditional solid state reaction method. The dependence of microwave dielectric properties on the crystal structure was analyzed in detail by the complex chemical bond theory (P–V-L theory) and classical dielectric polarizability theory. The dielectric constant (er) was mainly related to the density, bond ionicity and ionic polarizability of Mg2-x (Li0.5Ga0.5)xAl4Si5O18 ceramics. The quality factor (Q × f) was in relationship to the lattice energy, atomic packing fraction and centrosymmetry of [Si4Al2O18] hexagonal ring in cordierite crystal structure. The temperature coefficient of resonant frequency (τf) value was dominated by the bond energy and distortions of [MgO6] octahedron. The maximum values of Q × f = 50,560 GHz and er = 4.72 were obtained for undoped Mg2Al4Si5O18 and Mg1.98Li0.01Ga0.01Al4Si5O18, respectively.