Raman study of an electric-field-induced phase transition in (formula presented)

Electric-field-induced structural transition of a single crystal (formula presented) grown in the (001) direction was studied by use of Raman scattering spectroscopy. By comparing the changes in Raman spectra induced by the electric field with the temperature-dependent changes, we could confirm that the structural transition to tetragonal phase is initiated at a threshold electric field (formula presented) and completed at higher transition field (formula presented) In the electric-field range from (formula presented) to (formula presented) it is found that rhombohedral and tetragonal phases coexist. The lower threshold field (formula presented) is found to coincide with the field at which the strain rises abruptly in the strain electric-field hysteresis loop while the upper threshold field (formula presented) corresponds to the electric field where a slope change is observed in the high-field saturation region beyond the hysteresis loop.