Sodium niobate (NaNbO3, or NNO) is known to be antiferroelectric at temperatures between 45 and 753 K. Here we show experimentally the presence of the ferroelectric phase at temperatures between 100 and 830 K in the NNO crystals obtained by top-seeded solution growth. The ferroelectric phase and new phase transitions are evidenced using a combination of thermo-optical studies by variable angle spectroscopic ellipsometry, Raman spectroscopy analysis, and photoelectron emission microscopy. The possibility for strain-induced ferroelectricity in NNO is suggested.

Microelectronics and Materials Physics Laboratories University of Oulu PO Box 4500 FI 90014 Oulun yliopisto Finland Institute of Physics Academy of Sciences of the Czech Republic Na Slovance 2 182 21 Prague 8 Czech Republic

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