Deconvolution of Phonon-Phonon and Electron-Phonon Interactions from Phonon Line Width in Zr-Substituted BaTiO3

Abstract

Recently, one to one correlation between the electronic disorder, i.e., Urbach energy (Eu) and phonon width (Γ), has been observed [J. Phys. Chem. C 2022 126, 13946, Phys. Rev. B 2021 104, 245205], suggesting that scaling of electronic disorder and phonon line width has a common origin. It is believed that the introduction of finite perturbation into the crystal structure via chemical impurity such as doping or defect results in the potential fluctuations, which introduce states within the forbidden region of the band gap called Urbach tail states. Furthermore, such chemical impurities and defects act as a scattering center for the phonon waves, thereby affecting the phonon propagation length and phonon lifetime and altering phonon line shape. If the energy of discrete phonon mode lies within the energy spread of electronic continuum (which can be contributed by Urbach tail states), then there exists finite probability of electron-phonon coupling, whose signature can be realized by finite asymmetry of the interfering Raman mode and the asymmetry can scale with Eu. Hence, it is natural to expect that the Raman phonon line shape has information on phonon-phonon (pp) and electron-phonon (eph) interactions. Therefore, the total phonon width (Γtotal) at a given temperature “T” may be represented as Γtotal (T) ≈ Γpp(T) + Γeph(T). Here, we present temperature-dependent optical absorption spectroscopy and Raman spectroscopy measurements on Zr-substituted BaTiO3 to separate out the contribution of pp and eph to the total phonon width. Present studies are useful to understand the correlation of electronic and vibrational properties and their response toward the introduction of disorder into the system. © 2023 American Chemical Society.