Phase-Selective Growth of Ferroelectric and Antiferroelectric NaNbO₃ Thin Films

Ferroelectric and antiferroelectric materials play a critical role in electrical, optical, and thermal devices due to their electric field-controlled polarization switching capability. Controlling phase formation during thin film growth is essential for the design of these devices. In this study, we separately stabilized pure ferroelectric rhombohedral (N phase) and pure antiferroelectric orthorhombic (P phase) structures by precisely controlling the growth conditions of 70 nm-thick NaNbO₃ (NNO) thin films on (111)-oriented Nb-doped SrTiO₃ substrates. Through reciprocal space mappings and quarter-order diffraction measurements, a twinning structure within the NNO P-phase film is resolved. An antiferroelectric-to-ferroelectric phase transition, accompanied by a substantial enhancement in the electromechanical coupling response, is observed in the NNO P-phase film. Importantly, a phase diagram is constructed to delineate the growth window for each phase. This work provides a framework for synthesizing NNO thin films with controlled phases and offers a strategy for designing functional ferroelectric and antiferroelectric devices.