First-principle calculation and far infrared measurement for infrared-active modes of Ba(Mg1/3Ta2/3)O3

Abstract

A complex perovskite Ba(Mg1/3Ta2/3)O3 (BMT) ceramic sample with an almost ideal ordering of B-site cations was prepared by the conventional solid-state reactions and its infrared (IR) reflective spectrum in the range 50-5000 cm-1 was measured at room temperature. IR symmetry coordinates and their polar directions of the BMT sample were analyzed based on group theory. Eigenfrequencies, intensities, and transverse optical mode and longitudinal optical mode splitting of 16 IR vibrational modes were obtained based on the first-principle calculation and these modes were represented by the linear combinations of the symmetry coordinates. Far infrared reflection spectrum of BMT ceramic sample was fitted by the four-parameter semiquantum model (FPSQ) and assigned based on the calculation results. Generally, the heavier atoms with lower valence have more contributions to the lower frequency modes, while lighter atoms or higher valence atoms often have more contributions to the higher frequency modes. FPSQ fitting shows that the modes Eu(5) (∼241 cm -1) and Eu(4) (∼220 cm-1) dominated by the vibration of high-valence cation Ta5+ in [TaO 6] octahedra play the most important role for dielectric constant ε and dielectric loss tan δ. © 2010 The American Ceramic Society.