Temperature-dependent dielectric loss in BaTiO₃: Competition between tunnelling probability and electron-phonon interaction

The temperature-dependent impedance spectroscopy, optical absorption spectroscopy, and Raman spectroscopic measurements have been carried out on BaTiO₃ in the temperature range from 350 K to 430 K in order to understand the possible correlation between dielectric loss measured in terms of loss tangent (tan(δ)), band gap (Eg) and electron-phonon coupling parameter (λ_e-ph). It has been observed that in the tetragonal phase tan(δ) increases marginally, whereas in cubic phase tan(δ) shows a decreasing trend with increasing temperature. It has been observed that λ_e-ph increases with temperature and shows a sudden increase by almost two-fold at tetragonal to cubic transition temperature. The marginal increase in the value of tan(δ) with temperature in tetragonal phase is understood by considering the competition between the tunnelling of electron from valence to the conduction band and electron-phonon coupling, whereas; decrease in the value of tan(δ) in the cubic phase as a function of temperature may be due to the dominating contribution of electron-phonon coupling. Present investigations clearly establish the strong correlation between the temperature dependence of dielectric loss, the value of band gap, and electron-phonon interaction.