Synthesis, structure, and piezoelectric properties of ferroelectric and antiferroelectric NaNbO3 nanostructures

Abstract

NaNbO₃ cubes and nanowires have been synthesized by a hydrothermal-based method utilizing thin Nb foil and low-concentration NaOH solution with the presence of H₂O₂. The Na₂Nb₂O₆·H₂O precursor can be obtained under hydrothermal conditions at 200 °C for only 4 h. Both long-time hydrothermal treatment and calcination on the precursor nanowires can realize the transition from Na₂Nb₂O₆·H₂O nanowires to NaNbO₃ crystalline particles. However, the crystalline phases of the two products are different. NaNbO₃ microcubes obtained by long-time hydrothermal treatment are in the antiferroelectric phase with space group Pbma, while NaNbO₃ nanowires obtained by annealing Na₂Nb₂O₆·H₂O at 500 °C for 3 h are in the ferroelectric phase with space group P2₁ma. The experimental results from X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution electron microscopy (HRTEM) and Raman spectroscopy proved the difference between the crystalline phases of NaNbO₃ microcubes and nanowires. Piezoelectric force microscopy (PFM) analysis proved that NaNbO₃ nanowires exhibit piezoelectricity, while no piezoelectric response can be detected for NaNbO₃ microcubes synthesized by direct hydrothermal treatment.