Correlation of Phase Structure, Defect Relaxation, and Microwave Dielectric Properties in Low-Loss MgTiO₃ Ceramic...

Low-loss microwave dielectrics are of significant importance for the miniaturization and integration of microwave devices. In this paper, the ceramics of nominal composition MgTiO₃ (n = 3-6) are synthesized, and the correlations among their phase compositions, defect behaviors, and microwave dielectric properties are systematically investigated. The analyses indicate that the MgTiO₃ ceramics are a biphasic system consisting of hexagonal ilmenite-structured MgTiO₃ and cubic spinel-structured Mg₂TiO₄. The Rietveld refinement results demonstrate that as the n value increases, the content of the MgTiO₃ phase gradually increases, while that of the Mg₂TiO₄ phase decreases. The results of the thermally stimulated depolarization current (TSDC) indicate that the oxygen vacancy-related defects are considered to be the main types of defects in MgTiO₃. As the value of n increases, the increase of the MgTiO₃ phases with a more stable crystal structure leads to a gradual decrease in the concentration of oxygen vacancies. The MgTiO₃ ceramics exhibit excellent microwave dielectric properties at n = 6: ε_r = 17.55, Q × f = 284,600 GHz, and τ_f = -46.39 ppm/°C. In addition, the relationship between the dielectric constant and the electric field distribution is solved utilizing high-frequency structure simulator (HFSS) software, and the Q × f values are also predicted. The low-frequency dielectric temperature spectra and direct current pulse charge/discharge tests show that the low-loss MgTiO₃ ceramics can be good candidates for microwave capacitors even when operated under high-temperature conditions.