Far infrared reflection spectrum and IR-active modes of MgTiO3

Abstract

A MgTiO3 ceramic sample was synthesized by solid-state reactions and its far infrared (IR) reflection spectrum recorded. The IR-active vibrational modes of MgTiO3 were calculated using first-principle calculations and the modes were represented by linear combinations of the symmetry coordinates. Using the eigenfrequencies obtained by the density functional theory calculations as initial values, we fitted the infrared reflection spectrum using the four-parameter semiquantum (FPSQ) model and the Lorentz three-parameter classical model. The parameters (ΩjTO, ΩjLO, γjTO, γjLO in FPSQ fitting and Ωj, Sj, γj in the three-parameter model fitting) of seven of the eight modes predicted by group theory analysis were obtained. The transverse optical modes (in FPSQ) are assigned as 279cm−1 (Au), 383cm−1 (Au), 472cm−1 (Au), 673cm−1 (Au) and ∼262cm−1 (Eu), 317cm−1 (Eu), 416cm−1 (Eu), 531cm−1 (Eu). The modes Au (279cm−1), Eu (317cm−1), Au (472cm−1), and Eu (531cm−1), which contain larger components of cation vibrations, contribute most to the microwave dielectric constant and dielectric loss.