Manganese doping effects on interband electronic transitions, lattice vibrations, and dielectric functions of perovskite-type Ba _0.4Sr _0.6TiO ₃ ferroelectric ceramics

The Ba _0.4Sr _0.6-x Mn _x TiO ₃ (BSMT) ceramics with different Mn composition (from 1% to 10%) have been prepared via the conventional solid-state reaction sintering. The X-ray diffraction analysis shows that the ceramics are polycrystalline with the single perovskite phase. The lattice vibrations and optical properties have been investigated using Raman scattering, spectroscopic ellipsometry (SE), and infrared reflectance spectra. It was found that the optical bandgap for the BSMT ceramics is varied between 3.40 and 3.65 eV. The three first-order Raman-active phonon modes can be observed, and the frequency of the A ₁(LO ₃)/E(LO) mode shows a blue shift of 8 cm ^-1 with the Mn composition, which can be attributed to the distortion of the TiO ₆ octahedron. With increasing Mn composition, the frequency of the infrared-active TO ₄ mode decreases from 532 to 520 cm ^-1, owing to the local variation of the lattice constant induced by the Mn incorporation. Moreover, the optical functions of the ceramics from the far-infrared to ultraviolet region are obtained based on the SE and reflectance spectra, which is useful for the potential applications in ferroelectric-based optoelectronic devices.