Competing antiferroelectric and ferroelectric interactions inNaNbO3: Neutron diffraction and theoretical studies

Abstract

Neutron diffraction studies using powder samples have been used to understand the complex sequence of low temperature phase transitions of NaNbO3 in the temperature range from 12 K-350 K. Detailed Rietveld analysis of the diffraction data reveal that the antiferroelectric to ferroelectric phase transition occurs on cooling around 73 K while the reverse ferroelectric to antiferroelectric transition occurs on heating at 245 K. However, the former transformation is not complete till down to 12 K and there is unambiguous evidence for the presence of the ferroelectric R3c phase coexisting with an antiferroelectic phase (Pbcm) over a wide range of temperatures. The coexisting phases and reported anomalous smearing of the dielectric response akin to dipole glasses and relaxors observed in the same temperature range are consistent with competing ferroelectric and antiferroelectric interactions in NaNbO 3 . We have carried out theoretical lattice dynamical calculations which reveal that the free energies of the antiferroelectric Pbcm and ferroelectric R3c phases are nearly identical over a wide range of temperature. The small energy difference between the two phases is of interest as it explains the observed coexistence of these phases over a wide range of temperature. The computed double well depths and energy barriers from paraelectric Pm 3m to antiferroelectric Pbcm and ferroelectric R3c phases in NaNbO 3 are also quite similar, although the ferroelectric R3c phase has a slightly lower energy.

The Effects of Crystal Structure and Electronic Structure on Photocatalytic H2 Evolution and CO2 Reduction over Two Phases of Perovskite-Structured NaNbO3

“…The basic perovskite NaNbO 3 , which has a cubic structure with the space group of Pm3̅ m (Figure 1), is only stable at high temperature (>913 K). 31,36 When cooling down from high temperature, NaNbO 3 undergoes a series of phase transitions from cubic to rhombohedral via intermediate tetragonal and orthorhombic phases. At room temperature, the common phase of NaNbO 3 is an antiferroelectric orthorhombic (Figure 1).…”

Structures of K0.05Na0.95NbO3 (50–300 K) and K0.30Na0.70NbO3 (100–200 K)

“…Some studies on the sodium niobate end-member have been published by Darlington & Megaw (1973) and Mishra et al (2007), showing that at low temperature it undergoes an antiferroelectric ferroelectric phase transition from orthorhombic Pbcm to rhombohedral R3c. However, the potassium niobate endmember is rhombohedral, R3m, below 263 K (Hewat, 1973).…”

Antiferroelectricity induced by electric field in NaNbO3-based lead-free ceramics

“…1(b) and 1(c), these two peaks are apparent in ANKN0, ANKN1, and ANKN2 but completely disappear in ANKN4. According to a previous neutron diffraction study, 17 these are the characteristic antiferroelectric superlattice peaks that can be indexed as {11 3 4 } and {21 3 4 }. Therefore, the as-sintered ceramics of ANKN0, ANKN1, and ANKN2 are antiferroelectric while ANKN4 is ferroelectric at room temperature.…”

“…NaNbO 3 is a perovskite compound known for its complex structures and phase transitions. [13][14][15][16][17] Its solid solutions are of technological importance due to applications in lead-free piezoelectric devices [18][19][20] and high-temperature capacitors. 21 Although NaNbO 3 has been investigated for more than six decades, researchers are still debating whether it is antiferroelectric or ferroelectric at room temperature.…”