Bond characteristics and microwave dielectric properties of temperature-stable (1-x)Mg2TiO4-xLi4/3Ti5/3O4 (0.15 ≤ x ≤ 0.9) spinel solid solutions

In this work, spinel-structured (1-x)Mg2TiO4-xLi4/3Ti5/3O4 (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 (εr) was proved to be affected by the molar volume molecular polarizability and average bond ionicity (Afi). 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 (τf) was confirmed to be affected by the Ti–O bond energy. The optimal microwave dielectric properties (εr = 26.0, Q × f = 36,500 GHz, and τf = 2.4 ppm/ºC) were achieved at x = 0.75.