Bond characteristics and microwave dielectric properties of temperature-stable (1-x)Mg₂TiO₄-xLi_4/3Ti_5/3O₄ (0.15 ≤ x ≤ 0.9) spinel solid solutions

In this work, spinel-structured (1-x)Mg₂TiO₄-xLi_4/3Ti_5/3O₄ (0.15 ≤ x ≤ 0.9) ceramic samples were fabricated by a conventional solid-state method. The samples exhibited a disordered-to-ordered-to-disordered structural transition with an increase in the x value. The compositional dependence of microwave dielectric properties of the samples was discussed with respect to the chemical bond characteristics. The dielectric constant (ε_r) was proved to be affected by the molar volume molecular polarizability and average bond ionicity (Af_i). The quality factor (Q × f) was mainly dependent on the defect (i.e., Ti³⁺ and oxygen vacancy) population in the samples. Moreover, the temperature coefficient of the resonance frequency (τ_f) was confirmed to be affected by the Ti–O bond energy. The optimal microwave dielectric properties (ε_r = 26.0, Q × f = 36,500 GHz, and τ_f = 2.4 ppm/ºC) were achieved at x = 0.75.