Acoustic Mode Behavior in Ferroelectric Phase Transition of Li Doped ZnO Semiconductor and its Photoinduced Effect

Abstract

Acoustic phonon behavior and photoexcited effect in Li-doped ZnO ceramics were investigated at around the ferroelectric phase transition point Tc = 350 K by Brillouin scattering using a Sandercock-type tandem Fabry-Perot interferometer. The temperature dependence of Brillouin scattering spectra was obtained from 300 K to 500 K through Tc. A bunch of longitudinal-acoustic (LA) phonons did not show any anomaly at around Tc accompanied to the ferroelectric phase transition, although the LA mode is coupled to the spontaneous polarization in the ferroelectric phase with point group of 6 mm. The result indicates that the mechanism of the ferroelectric phase transition is not an order-disorder type related to size mismatch of the doped Li cation. No photoinduced effect was observed in the LA phonon bunch around Tc under ultraviolet (UV) excitation with energies higher than the band gap energy, although the intensity of base line in Brillouin scattering spectrum increased under UV. The component of base line includes an emission spectrum and /or a central peak component, which might be related to an electronic ferroelectricity.