Visualization of the phonon evolution behavior in NaNbO3 single crystal during field-induced phase transition by in situ Raman spectroscopy

NaNbO3 (NN) is a significant lead-free alternative for pulse power systems or nonvolatile memories due to its antiferroelectric P phase at room temperature. However, a comparable free energy between P phase and another ferroelectric Q phase leads to an irreversible transition from P to Q phase just under a weak electric field, which results in the unobservable double hysteresis loops. In addition, recent studies reveal that the critical field needed during the transition process is inconsistent between in situ microstructure characterization and macroscopic polarization measurement. Consequently, the intricate field-induced phase transition in NN is perplexing. Based on high sensitivity of Raman spectroscopy to symmetry breaking in lattices, this work systematically investigates the in situ Raman spectra of NN single crystals, analyzing the evolution and depolarization behavior of various phonons under an electric field. Correspondingly, the transition from P to Q phase is determinately identified, accompanied by in-depth understanding of the phonon dynamics of field-induced phase transition. This present work provides a reliable experimental foundation for further probing on the transition mechanism of ferroelectric/antiferroelectric order in dielectrics, as well as facilitating the performance control and application development of NN-based devices.