Abstract
We report on the experimental and theoretical study of the lattice dynamics in Ba0.7Sr0.3TiO3 in 20–900 K temperature range. Complex dielectric response in the terahertz and far infrared range was evaluated from the time-domain THz transmission spectra and infrared reflectivity by means of damped harmonic oscillator models in classical and factorized form of the dielectric function. The anisotropic dielectric function in the ferroelectric phases was extracted using the Bruggeman model of the effective medium approximation. The fitted parameters of the temperature-dependent Slater-type vibrations (soft mode and central mode, CM) were compared with those obtained from ab initio simulations. The role of the lattice phonons and CM in the dielectric anomaly is discussed.
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