The dielectric properties of La(Mg_(0.5)Ti_(0.5))O _3 ceramics studied by Raman-scattering, infrared reflectivity spectroscopy, and first-principles calculations

摘要

La(Mg_(0.5)Ti_(0.5))O_3 (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 OI and OII 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.