The dielectric properties of La(Mg_0.5Ti_0.5)O ₃ ceramics studied by Raman-scattering, infrared reflectivity spectroscopy, and first-principles calculations

La(Mg_0.5Ti_0.5)O₃ (LMT) ceramics were prepared by either the solid-state reaction (LMT)_SS or the citric-acid chemical method (LMT)_CA. A combination of Raman scattering, infrared reflectivity, and first-principles calculations was carried out to elucidate the correlation between lattice dynamics and the dielectric properties of these materials. Twelve Raman-active phonons are observed in both samples, displaying similar frequency positions. Interestingly, the A _g phonon (g₁₁ mode) of (LMT)_SS at about 717cm^-1 involving the oxygen octahedron breathing vibrations demonstrates a narrower linewidth, suggesting its better crystallinity. Furthermore, an infrared-active u₂ phonon band due to the vibrations of O_I and O_II layers, which possesses the largest oscillator strength, exhibits stronger intensity for (LMT)_SS, as compared with those for (LMT)_CA. Additionally, the Q × f values (the product of dielectric Q values and measurement frequency) of (LMT) _SS estimated from either microwave cavity or infrared spectroscopic measurements are larger than those of (LMT)_CA. These results indicate that the better coherence of lattice vibrations in (LMT)_SS leads to its higher Q × f value, providing evidence for a strong connection between optical spectroscopic behavior and microwave dielectric characteristics in these materials.