Optical phonons in ferroelectric-semiconductor Zn0.8Li0.2O single crystal studied by micro-Raman scattering

Micro-probed Raman scattering spectra of ferroelectric-semiconductor Zn0.8Li0.2O single crystal have been observed as a function of temperature for several scattering geometries. The crystal orientation of the small single crystal has been determined by an angular dependence study of the peak intensity of the spectra at room temperature. Observed peak frequencies are in agreement with those of the pure ZnO wurtzite crystal. Though the shape of the Raman spectra does not change extremely near the phase transition temperature, the temperature dependence of the peak position shows a small cusp like anomaly. In the low frequency region, no new modes or mode softening were observed. These results indicate that the ferroelectric-phase transition in Zn0.8Li0.2O system is induced by the electronic origin rather than the ionic instability.