<i>In situ</i> Raman scattering investigation of field-induced phase transition behavior in Na1+<i>x</i>NbO3 ceramics via nonstoichiometric regulation

NaNbO3 is regarded as an ideal model for elucidating lattice distortion in dielectrics due to its complex structural phase transition under various external fields. In particular, it has garnered significant attention because of its irreversible electric-field-induced transition from antiferroelectric to ferroelectric phases and dielectric relaxation with varying temperatures. At present, numerous studies have explored the evolution of NbO6 octahedra in NaNbO3, while investigations into the role of Na+ remain scarce during phase transition. Moreover, traditional microstructure characterization techniques, such as x-ray diffraction, generally fail to capture the displacement details of lighter Na+ ions, making it particularly challenging to analyze their influence on the phase transition of NaNbO3. In this work, Na1+xNbO3 series with different Na contents are constructed by adjusting the nonstoichiometric ratio of A-site Na atoms. Based on in situ Raman spectra with varying electric fields and temperatures, an in-depth insight into the phase transition is realized, accompanied by revealing the related physical mechanism. The findings will make contribution to identify the regulation of Na+ on the phase transition in NaNbO3 from the perspective of phonon evolution, further clarifying the conversion origin among various electrical orders. In addition, it provides a critical foundation for the design and development of NaNbO3-based electronic devices.